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  • Articles  (18,109)
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  • Springer  (18,109)
  • 1995-1999  (18,109)
  • 1999  (18,109)
  • Biology  (17,296)
  • Natural Sciences in General  (1,069)
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  • Books
  • Articles  (18,109)
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  • 1995-1999  (18,109)
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  • 1
    Electronic Resource
    Electronic Resource
    Cable analysis of a motor-nerve terminal branch in a volume conductor (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 1-17 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract An equivalent electrical circuit is given for a branch of an amphibian motor-nerve terminal in a volume conductor. The circuit allows for longitudinal current flow inside the axon as well as between the axon and its Schwann cell sheath, and also for the radial leakage of current through the Schwann cell sheath. Analytical and numerical solutions are found for the spatial and time dependence of the membrane potential resulting from the injection of depolarizing current pulses by external electrodes at one or two separate locations on the terminal. These solutions show that the depolarization at an injection site can cause a hyperpolarization at sites a short distance away. This effect becomes more pronounced in a short terminal with sealed-end boundary conditions. The hyperpolarization provides a possible explanation for recent experimental results, which show that the average quantal release due to a test depolarizing current pulse delivered by an electrode at one site on a nerve terminal is reduced by the application of an identical conditioning pulse at a neighbouring site.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1998.0066
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  • 2
    Electronic Resource
    Electronic Resource
    A mathematical model for simulating virus transport through synthetic barriers (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 113-140 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Synthetic barriers such as gloves, condoms and masks are widely used in efforts to prevent disease transmission. Due to manufacturing defects, tears arising during use, or material porosity, there is inevitably a risk associated with use of these barriers. An understanding of virus transport through the relevant passageways would be valuable in quantifying the risk. However, experimental investigations involving such passageways are difficult to perform, owing to the small dimensions involved. This paper presents a mathematical model for analyzing and predicting virus transport through barriers. The model incorporates a mathematical description of the mechanisms of virus transport, which include carrier-fluid flow, Brownian motion, and attraction or repulsion via virus-barrier interaction forces. The critical element of the model is the empirically determined rate constant characterizing the interaction force between the virus and the barrier. Once the model has been calibrated through specification of the rate constant, it can predict virus concentration under a wide variety of conditions. The experiments used to calibrate the model are described, and the rate constants are given for four bacterial viruses interacting with a latex membrane in saline. Rate constants were also determined for different carrier-fluid salinities, and the salt concentration was found to have a pronounced effect. Validation experiments employing laser-drilled pores in condoms were also performed to test the calibrated model. Model predictions of amount of transmitted virus through the drilled holes agreed well with measured values. Calculations using determined rate constants show that the model can help identify situations where barrier-integrity tests could significantly underestimate the risk associated with barrier use.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1998.0080
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  • 3
    Electronic Resource
    Electronic Resource
    Analysis of intra-uterine fluid motion induced by uterine contractions (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 221-238 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Evaluation of the fluid flow pattern in a non-pregnant uterus is important for understanding embryo transport in the uterus. Fertilization occurs in the fallopian tube and the embryo (fertilized ovum) enters the uterine cavity within 3 days of ovulation. In the uterus, the embryo is conveyed by the uterine fluid for another 3 to 4 days to a successful implantation site at the upper part of the uterus. Fluid movements within the uterus may be induced by several mechanisms, but they seem to be dominated by myometrial contractions. Intra-uterine fluid transport in a sagittal cross-section of the uterus was simulated by a model of wall-induced fluid motion within a two-dimensional channel. The time-dependent fluid pattern was studied by employing the lubrication theory. A comprehensive analysis of peristaltic transport resulting from symmetric and asymmetric contractions is presented for various displacement waves on the channel walls. The results provide information on the flow field and possible trajectories by which an embryo may be transported before implantation at the uterine wall.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1998.0069
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  • 4
    Electronic Resource
    Electronic Resource
    Replication potential of cells via the protein kinase C-MAPK pathway: Application of a mathematical model (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 379-398 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A mechanistically based mathematical model is used to investigate some of the important factors in priming hepatocytes to enter the G1 phase of the cell cycle. The model considers all of the relevant biochemical mechanisms from signal-receptor binding to the elevation of AP-1(activation protein transcription factor) levels. Focus is centered on the chain of biochemical events governing the sequential activation of protein kinase C (PKC), mitogen-activated protein kinase (MAPK) and AP-1. Factors such as amplitude and duration of growth factors signals, the kinetics of guanosine diphosphate (GDP) to guanosine triphosphate (GTP) conversion, and the negative feedback control mechanisms governing initial steps in cellular replication were theoretically examined. The results of our theoretical assessments support the finding that specific mutations along the PKC-AP1 pathways can have a critical effect on the rate at which cells enter the division cycle.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1998.0077
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  • 5
    Electronic Resource
    Electronic Resource
    Velocity and stability of solitary planar travelling wave solutions of intracellular [Ca]2+ (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 273-301 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Normal cardiac muscle contraction occurs in response to a rapid rise followed by a slower decay in intracellular calcium concentration. When cardiac muscle cells are loaded with calcium, an intracellular store releases calcium into the cytosol by the process of calcium-induced calcium release (CICR). This release contributes to the rise in intracellular calcium which in turn triggers contraction. We use two qualitative piecewise linear reaction-diffusion models of this behaviour to investigate the speed, stability and waveform of plane waves using singular perturbation techniques.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1998.0081
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  • 6
    Electronic Resource
    Electronic Resource
    Numerical simulations of stochastic circulatory models (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 365-377 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Properties of two of the stochastic circulatory models theoretically introduced by Smith et al., 1997, Bull. Math. Biol. 59, 1–22 were investigated. The models assumed the gamma distribution of the cycle time under either the geometric or Poisson elimination scheme. The reason for selecting these models was the fact that the probability density functions of the residence time of these models are formally similar to those of the Bateman and gamma-like function models, i.e., the two common deterministic models. Using published data, the analytical forms of the probability density functions of the residence time and the distributions of the simulated values of the residence time were determined on the basis of the deterministic models and the stochastic circulatory models, respectively. The Kolmogorov-Smirnov test revealed that even for 1000 xenobiotic particles, i.e., a relatively small number if the particles imply drug molecules, the probability density functions of the residence time based on the deterministic models closely matched the distributions of the simulated values of the residence time obtained on the basis of the stochastic circulatory models, provided that parameters of the latter models fulfilled selected conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1998.0094
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  • 7
    Electronic Resource
    Electronic Resource
    About deterministic extinction in ratio-dependent predator-prey models (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 19-32 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Ratio-dependent predator-prey models set up a challenging issue regarding their dynamics near the origin. This is due to the fact that such models are undefined at (0, 0). We study the analytical behavior at (0, 0) for a common ratio-dependent model and demonstrate that this equilibrium can be either a saddle point or an attractor for certain trajectories. This fact has important implications concerning the global behavior of the model, for example regarding the existence of stable limit cycles. Then, we prove formally, for a general class of ratio-dependent models, that (0, 0) has its own basin of attraction in phase space, even when there exists a non-trivial stable or unstable equilibrium. Therefore, these models have no pathological dynamics on the axes and at the origin, contrary to what has been stated by some authors. Finally, we relate these findings to some published empirical results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1998.0072
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  • 8
    Electronic Resource
    Electronic Resource
    Parkinsonian tremor and simplification in network dynamics (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 157-177 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract We explore the behavior of richly connected inhibitory neural networks under parameter changes that correspond to weakening of synaptic efficacies between network units, and show that transitions from irregular to periodic dynamics are common in such systems. The weakening of these connections leads to a reduction in the number of units that effectively drive the dynamics and thus to simpler behavior. We hypothesize that the multiple interconnecting loops of the brain’s motor circuitry, which involve many inhibitory connections, exhibit such transitions. Normal physiological tremor is irregular while other forms of tremor show more regular oscillations. Tremor in Parkinson’s disease, for example, stems from weakened synaptic efficacies of dopaminergic neurons in the nigro-striatal pathway, as in our general model. The multiplicity of structures involved in the production of symptoms in Parkinson’s disease and the reversibility of symptoms by pharmacological and surgical manipulation of connection parameters suggest that such a neural network model is appropriate. Furthermore, fixed points that can occur in the network models are suggestive of akinesia in Parkinson’s disease. This model is consistent with the view that normal physiological systems can be regulated by robust and richly connected feedback networks with complex dynamics, and that loss of complexity in the feedback structure due to disease leads to more orderly behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1998.0086
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  • 9
    Electronic Resource
    Electronic Resource
    Computational experience with a parallel algorithm for tetrangle inequality bound smoothing (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 987-1008 
    Details
    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Determining molecular structure from interatomic distances is an important and challenging problem. Given a molecule with n atoms, lower and upper bounds on interatomic distances can usually be obtained only for a small subset of the $$\frac{{n(n - 1)}}{2}$$ atom pairs, using NMR. Given the bounds so obtained on the distances between some of the atom pairs, it is often useful to compute tighter bounds on all the $$\frac{{n(n - 1)}}{2}$$ pairwise distances. This process is referred to as bound smoothing. The initial lower and upper bounds for the pairwise distances not measured are usually assumed to be 0 and ∞. One method for bound smoothing is to use the limits imposed by the triangle inequality. The distance bounds so obtained can often be tightened further by applying the tetrangle inequality—the limits imposed on the six pairwise distances among a set of four atoms (instead of three for the triangle inequalities). The tetrangle inequality is expressed by the Cayley—Menger determinants. For every quadruple of atoms, each pass of the tetrangle inequality bound smoothing procedure finds upper and lower limits on each of the six distances in the quadruple. Applying the tetrangle inequalities to each of the ( 4 n ) quadruples requires O(n 4) time. Here, we propose a parallel algorithm for bound smoothing employing the tetrangle inequality. Each pass of our algorithm requires O(n 3 log n) time on a CREW PRAM (Concurrent Read Exclusive Write Parallel Random Access Machine) with $$O\left( {\frac{n}{{\log n}}} \right)$$ processors. An implementation of this parallel algorithm on the Intel Paragon XP/S and its performance are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1999.0123
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  • 10
    Electronic Resource
    Electronic Resource
    Membrane skeleton detachment in spherical and cylindrical microexovesicles (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 1019-1030 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract We observed that amphiphile-induced microexovesicles may be spherical or cylindrical, depending on the species of the added amphiphile. The spherical microexovesicle corresponds to an extreme local difference between the two monolayer areas of the membrane segment with a fixed area, while the cylindrical microexovesicle corresponds to an extreme local area difference if the area of the budding segment is increased due to lateral influx of anisotropic membrane constituents. Protein analysis showed that both types of vesicles are highly depleted in the membrane skeleton. It is suggested that a partial detachment of the skeleton in the budding region is favoured due to accumulated skeleton shear deformations in this region.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1999.0128
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  • 11
    Electronic Resource
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    Book review (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 1209-1210 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1999.0135
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  • 12
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    Controlling chaos in ecology: From deterministic to individual-based models (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 1187-1207 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The possibility of chaos control in biological systems has been stimulated by recent advances in the study of heart and brain tissue dynamics. More recently, some authors have conjectured that such a method might be applied to population dynamics and even play a nontrivial evolutionary role in ecology. In this paper we explore this idea by means of both mathematical and individual-based simulation models. Because of the intrinsic noise linked to individual behavior, controlling a noisy system becomes more difficult but, as shown here, it is a feasible task allowed to be experimentally tested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1999.0141
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  • 13
    Electronic Resource
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    Persistence in metabolic nets (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 573-595 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract In an attempt to improve the understanding of complex metabolic dynamic phenomena, we have analysed several ‘metabolic networks’, dynamical systems which, under a single formulation, take into account the activity of several catalytic dissipative structures, interconnected by substrate fluxes and regulatory signals. These metabolic networks exhibit a rich variety of self-organized dynamic patterns, with e.g., phase transitions emerging in the whole activity of each network. We apply Hurst’s R/S analysis to several time series generated by these metabolic networks, and measure Hurst exponents H 〈 0.5 in most cases. This value of H, indicative of antipersistent processes, is detected at very high significance levels, estimated with detailed Monte Carlo simulations. These results show clearly the considered type of metabolic networks exhibit long-term memory phenomena.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1999.0103
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  • 14
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    Book reviews (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 597-600 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1998.0092
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  • 15
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    RNA structures with pseudo-knots: Graph-theoretical, combinatorial, and statistical properties (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 437-467 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The secondary structures of nucleic acids form a particularly important class of contact structures. Many important RNA molecules, however, contain pseudo-knots, a structural feature that is excluded explicitly from the conventional definition of secondary structures. We propose here a generalization of secondary structures incorporating ‘non-nested’ pseudo-knots, which we call bi-secondary structures, and discuss measures for the complexity of more general contact structures based on their graph-theoretical properties. Bi-secondary structures are planar trivalent graphs that are characterized by special embedding properties. We derive exact upper bounds on their number (as a function of the chain length n) implying that there are fewer different structures than sequences. Computational results show that the number of bi-secondary structures grows approximately like 2.35n. Numerical studies based on kinetic folding and a simple extension of the standard energy model show that the global features of the sequence-structure map of RNA do not change when pseudo-knots are introduced into the secondary structure picture. We find a large fraction of neutral mutations and, in particular, networks of sequences that fold into the same shape. These neutral networks percolate through the entire sequence space.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1998.0085
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  • 16
    Electronic Resource
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    A hydrostatic Michell framework supports frog lungs (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 683-700 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A braced framework of tubular struts, in the walls and air spaces of frog lungs, suspends the respiratory surface and holds the lung open at zero transmural pressure withstanding imploding forces created by abdominal viscera, much as would the supports of a bell tent. The struts are tubes, having a larger second moment of area than do solid struts of the same cross-sectional area, and so are stronger, and contain pulmonary vessels within a flexible wall. The orthogonal arrangement of the struts in the framework, explained in part by Maxwell’s Lemma and Michell’s Theorem, strengthens the framework and minimizes its weight; orthogonality is maintained as the lungs change size. A model is presented, in which a frog might control pre-and post-pulmonary vascular resistances and, hence, blood volume in the struts, without compromising pulmonary perfusion. Such adjustments could vary the area of lung and the extent of perfused capillaries exposed to pulmonary gas, helping match the lung’s surface area, weight and metabolic load to activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1999.0104
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  • 17
    Electronic Resource
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    Theory of fast neurotransmitter release control based on voltage-dependent interaction between autoreceptors and proteins of the exocytotic machinery (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 701-725 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A molecular-level theory is constructed for the control of fast neurotransmitter release, based on recent experimental findings that depolarization shifts presynaptic autoreceptors to a low affinity state and that an autoreceptor must be bound to a transmitter before it can become associated with the exocytotic apparatus. It is assumed that such an association blocks release; experimental support for this assumption is cited. The theory provides mechanisms for key experimental results concerning the essence of the matter, what controls the time course of evoked release? The same general model can account for both evoked and spontaneous release. The new theory can be regarded as a molecular implementation of the (phenomenological) calcium-voltage hypothesis that was suggested earlier.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1999.0107
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  • 18
    Electronic Resource
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    Book reviews (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 799-805 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
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    URL: http://dx.doi.org/10.1006/bulm.1999.0099
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  • 19
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    Cellular automaton models for competition in patchy environments: Facilitation, inhibition, and tolerance (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 625-649 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract We have developed cellular automaton models for two species competing in a patchy environment. We have modeled three common types of competition: facilitation (in which the winning species can colonize only after the losing species has arrived) inhibition (in which either species is able to prevent the other from colonizing) and tolerance (in which the species most tolerant of reduced resource levels wins). The state of a patch is defined by the presence or absence of each species. State transition probabilities are determined by rates of disturbance, competitive exclusion, and colonization. Colonization is restricted to neighboring patches. In all three models, disturbance permits regional persistence of species that are excluded by competition locally. Persistence, and hence diversity, is maximized at intermediate disturbance frequencies. If disturbance and dispersal rates are sufficiently high, the inferior competitor need not have a dispersal advantage to persist. Using a new method for measuring the spatial patterns of nominal data, we show that none of these competition models generates patchiness at equilibrium. In the inhibition model, however, transient patchiness decays very slowly. We compare the cellular automaton models to the corresponding mean-field patch-occupancy models, in which colonization is not restricted to neighboring patches and depends on spatially averaged species frequencies. The patch-occupancy model does an excellent job of predicting the equilibrium frequencies of the species and the conditions required for coexistence, but not of predicting transient behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1999.0090
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  • 20
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    Reaction and diffusion on growing domains: Scenarios for robust pattern formation (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 1093-1120 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract We investigate the sequence of patterns generated by a reaction—diffusion system on a growing domain. We derive a general evolution equation to incorporate domain growth in reaction—diffusion models and consider the case of slow and isotropic domain growth in one spatial dimension. We use a self-similarity argument to predict a frequency-doubling sequence of patterns for exponential domain growth and we find numerically that frequency-doubling is realized for a finite range of exponential growth rate. We consider pattern formation under different forms for the growth and show that in one dimension domain growth may be a mechanism for increased robustness of pattern formation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1999.0131
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  • 21
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    On the evolution of pure winner and loser effects: A game-theoretic model (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 1151-1186 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract The persistence of linear dominance hierarchies is often attributed to higher probabilities of a win after a win or a loss after a loss in agonistic interactions, yet there has been no theory on the evolution of such prior-experience effects. Here an analytic model, based on the idea that contests are determined by subjective perceptions of resource-holding potential (RHP) which animals may revise in the light of experience, demonstrates that winner and loser effects can evolve through round-robin competition among triads of animals drawn randomly from their population, and that the probability of a hierarchy increases with the strength of the combined effect. The effects are pure, in the sense that a contestant observes neither its own RHP nor its opponent’s RHP or RHP perception or win—loss record; and so the strength of an effect is unmodified by the RHPs of particular individuals, but depends on the distribution of RHP among the population at large. The greater the difference between an individual’s and its opponent’s RHP perception, the more likely it is to win a contest; however, if it overestimates its RHP, then the cost of fighting increases with the overestimate. A winner or loser effect exists only if the fitness gain of the beta individual in a hierarchy, relative to that of the alpha, is less than 0.5. Then a loser effect can exist alone, or it can coexist with a winner effect; however, there cannot exist a winner effect without a loser effect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1999.0137
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  • 22
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    Multiple attractors, saddles, and population dynamics in periodic habitats (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 1121-1149 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Mathematical models predict that a population which oscillates in the absence of time-dependent factors can develop multiple attracting final states in the advent of periodic forcing. A periodically-forced, stage-structured mathematical model predicted the transient and asymptotic behaviors of Tribolium (flour beetle) populations cultured in periodic habitats of fluctuating flour volume. Predictions included multiple (2-cycle) attractors, resonance and attenuation phenomena, and saddle influences. Stochasticity, combined with the deterministic effects of an unstable ’saddle cycle’ separating the two stable cycles, is used to explain the observed transients and final states of the experimental cultures. In experimental regimes containing multiple attractors, the presence of unstable invariant sets, as well as stochasticity and the nature, location, and size of basins of attraction, are all central to the interpretation of data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1006/bulm.1999.0136
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  • 23
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    Book review (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 207-208 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
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    URL: http://dx.doi.org/10.1006/bulm.1998.0071
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  • 24
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    Modelling the internalization of labelled cells in tumour spheroids (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 601-623 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract In this paper a mathematical model is developed to describe the migration of labelled particles within a multicell spheroid. In the model, spatial variations in cell proliferation and death create an internal velocity field which leads to redistribution of the labelled and unlabelled cells. By applying a range of numerical and analytical techniques to the model equations, it is possible to show that, whilst the speed with which the labelled cells migrate through the tumour is independent of the type of cells that are labelled, their limiting distribution depends crucially on whether inert polystyrene microspheres or live tumour cells are labelled. These predictions are shown to be in good qualitative agreement with independent experimental results.
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    URL: http://dx.doi.org/10.1006/bulm.1999.0089
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  • 25
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    Book reviews (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 1009-1013 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
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    URL: http://dx.doi.org/10.1006/bulm.1999.0110
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    Modeling the T-cell dynamics and pathogenesis of HTLV-I infection (1999)
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    Bulletin of mathematical biology 61 (1999), S. 935-947 
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    Notes: Abstract Human T-cell lymphotropic virus type I (HTLV-I) infection in humans causes a chronic infection of CD4+ T cells, and is associated with various disease outcomes, among them with the development of adult T-cell leukemia (ATL). The T-cell dynamics after HTLV-I infection can be described in a mathematical model with coupled differential equations. The infection process is modeled assuming cell-to-cell infection of CD4+ T cells. The model allows for CD4+ T cell subsets of susceptible, latently infected and actively infected cells as well as for leukemia cells. Latently infected T cells may harbor the virus for several years until they become activated and able to infect susceptible T cells. Uncontrolled proliferation of CD4+ T cells with monoclonal DNA-integration of HTLV-I results in the development of ATL. The model describes basic features that characterize HTLV-I infection; the chronic infection of CD4+ T cells, the increasing number of abnormal cells and the possible progression to ATL.
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    Size hierarchy and stability in competitive plant populations (1999)
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    Bulletin of mathematical biology 61 (1999), S. 949-961 
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    Notes: Abstract A neighbourhood-based competition model for plant individuals is studied to evaluate how a hierarchical structure related to size may emerge in plant communities. It is shown by numerical simulations and linear stability analysis that many stable states exist in the hierarchical structure when both the total number of individuals and the degree of asymmetry of competition are high. When the hierarchical structures are self-organized by the dynamic instability of the homogeneous state due to non-linearity of competition, it is proved that these states are always locally stable. The relevance of the results to size structures in real plant communities (boreal forests vs tropical and temperate forests) is discussed. This is suggested to be the mechanism responsible for the coexistence of species in plant communities.
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    Comparative dynamics of three models for host-parasitoid interactions in a patchy environment (1999)
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    Bulletin of mathematical biology 61 (1999), S. 141-155 
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    Notes: Abstract Phenomenological models represent a simplified approach to the study of complex systems such as host-parasitoid interactions. In this paper we compare the dynamics of three phenomenological models for host-parasitoid interactions developed by May (1978), May and Hassell (1981) and May et al. (1981). The essence of the paper by May and Hassell (1981) was to define a minimum number of parameters that would describe the interactions, avoiding the technical difficulties encountered when using models that involve many parameters, yet yielding a system of equations that could capture the essence of real world interactions in patchy environments. Those studies dealt primarily with equilibrium and coexistence phenomena. Here we study the dynamics through bifurcation analysis and phase portraits in a much wider range of parameter values, carrying the models beyond equilibrium states. We show that the dynamics can be either stable or chaotic depending on the location of a damping term in the equations. In the case of the stable system, when host density dependence acts first, a stable point is reached, followed by a closed invariant curve in phase space that first increases then decreases, finally returning to an asymptotically stable point. Chaos is not seen. On the other hand, when parasitoid attack occurs before host density dependence, chaos is inevitably apparent. We show, as did May et al. (1981) and stated earlier byWang and Gutierrez (1980), that the sequence of events in host-parasitoid interactions is crucial in determining their stability. In a chaotic state the size of the host (e.g., insect pests) population becomes unpredictable, frequently becoming quite large, a biologically undesirable outcome. From a mathematical point of view the system is of interest because it reveals how a strategically placed damping term can dramatically alter the outcome. Our study, reaching beyond equilibrium states, suggests a strategy for biological control different from that of May et al. (1981).
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    Effects of parasitism over two competing host populations leading to persistence (1999)
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    Bulletin of mathematical biology 61 (1999), S. 179-205 
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    Notes: Abstract In this paper we study the uniform persistence (UP) of an association of two competing host species sharing a directly transmitted macroparasite. Like predators, parasites can regulate UP while the hosts are either coexisting or in a dominance relationship without any infections, but cannot regulate UP in case the hosts are in bistability. The regulatory mechanism depends on the relationships between the parameters, such as host intrinsic growth rate, host carrying capacity, susceptibility, parasite pathogenicity and the magnitude of parasite aggregation. In the case of coexistence the parametric space for UP is more than that for global stability of the host-parasite equilibrium, but is less than that for UP in the case of dominance. In the case of dominance, the parasites can alter the competitive outcome locally or can enhance the local exclusion of the inferior competitor and thus, unlike the predation, parasitism has an beneficial effect over competition. We derive explicitly the range of the values of ratios of the rates of reproduction and survivorship of the hosts, and also of the values of the degree of aggregations, with which macroparasites are not effective in maintaining its beneficial effect over competition. Finally our results support the body-size hypothesis of Price et al. (1988), with possible explanations of certain exceptional examples of the hypothesis.
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    Parametric-equation representation of biconcave erythrocytes (1999)
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    Bulletin of mathematical biology 61 (1999), S. 209-220 
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    Notes: Abstract The representation of the shape of a biconcave erythrocyte by a set of three parametric equations was achieved by using the expressions that transform the curvilinear coordinates from the disc-cyclide coordinate system [denoted J2R; Moon and Spencer (1988), Field Theory Handbook, Springer-Verlag, Berlin] to Cartesian coordinates. The equations are products of elliptic functions, so the challenge was to relate the three major ’shape-defining’ measurements of the human erythrocyte in Cartesian coordinates to three parameters in the new curvilinear coordinates, to give a realistic representation of the shape of the membrane-surface. The relationships between the coefficients of the Cartesian degree-4 surface that describes the discocyte and the coordinate transformation equations were derived with the aid of Mathematica; and the membrane-surface of the cell was drawn using the ParametricPlot3D function in this ‘package’. By having the erythrocyte shape expressed in its new form it is readily amenable to further transformations that might be used to model those changes in shape that are seen when the cells are immersed in media of various osmolalities, or when they change metabolic ’states’. On the other hand, the relationship between the coefficients of the Cartesian expression for the disc-cyclide surface is relevant to image analysis of erythrocytes, as determined by physical methods that rely on Cartesian imaging ’slices’. These methods include confocal microscopy and various nuclear magnetic resonance microimaging procedures.
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    A physical-biological coupled model for algal dynamics in lakes (1999)
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    Bulletin of mathematical biology 61 (1999), S. 239-272 
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    Notes: Abstract A coupled model is presented for simulating physical and biological dynamics in fresh water lakes. The physical model rests upon the assumption that the turbulent kinetic energy in a water column of the lake is fully contained in a mixed layer of variable depth. Below this layer the mechanical energy content is assumed to vanish. Additionally, the horizontal currents are ignored. This one-dimensional two-layered model describes the internal conversion of the mechanical and thermal energy input from the atmosphere into an evolution of the mixed layer depth by entrainment and detrainment mechanisms. It is supposed to form the physical domain in which the simulation of the biological processes takes place. The biological model describes mathematically the typical properties of phyto-and zooplankton, their interactions and their response to the physical environment. This description then allows the study of the behaviour of Lagrangian clusters of virtual plankton that are subjected to such environments. The essence of the model is the dynamical simulation of an arbitrary number of nutrient limited phytoplankton species and one species of zooplankton. The members of the food web above and below affect the model only statically. The model is able to reproduce the typical progression of a predator-prey interaction between phyto-and zooplankton as well as the exploitative competition for nutrients between two phytoplankton species under grazing pressure of Daphnia. It suggests that the influence of the biological system on the physical system results in a weak increase of the surface temperature for coupled simulations, but a considerably higher seasonal thermocline in spring and a lower one in autumn.
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    Zooplankton mortality and the dynamical behaviour of plankton population models (1999)
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    Bulletin of mathematical biology 61 (1999), S. 303-339 
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    Notes: Abstract We investigate the dynamical behaviour of a simple plankton population model, which explicitly simulates the concentrations of nutrient, phytoplankton and zooplankton in the oceanic mixed layer. The model consists of three coupled ordinary differential equations. We use analytical and numerical techniques, focusing on the existence and nature of steady states and unforced oscillations (limit cycles) of the system. The oscillations arise from Hopf bifurcations, which are traced as each parameter in the model is varied across a realistic range. The resulting bifurcation diagrams are compared with those from our previouswork, where zooplankton mortality was simulated by a quadratic function—here we use a linear function, to represent alternative ecological assumptions. Oscillations occur across broader ranges of parameters for the linear mortality function than for the quadratic one, although the two sets of bifurcation diagrams show similar qualitative characteristics. The choice of zooplankton mortality function, or closure term, is an area of current interest in the modelling community, and we relate our results to simulations of other models.
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    Use of Bayes theorem to correct size-specific sampling bias in growth data (1999)
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    Bulletin of mathematical biology 61 (1999), S. 355-363 
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    Notes: Abstract The bayesian decomposition of posterior distribution was used to develop a likelihood function to correct bias in the estimates of population parameters from data collected randomly with size-specific selectivity. Positive distributions with time as a parameter were used for parametrization of growth data. Numerical illustrations are provided. The alternative applications of the likelihood to estimate selectivity parameters are discussed.
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    Probability density functions useful for parametrization of heterogeneity in growth and allometry data (1999)
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    Bulletin of mathematical biology 61 (1999), S. 1015-1016 
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    URL: http://dx.doi.org/10.1006/bulm.1999.0124
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    Pattern formation of scale cells in lepidoptera by differential origin-dependent cell adhesion (1999)
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    Bulletin of mathematical biology 61 (1999), S. 807-828 
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    Notes: Abstract We present a model for the formation of parallel rows of scale cells in the developing adult wing of moths and butterflies. Precursors of scale cells differentiate throughout each epithelial monolayer and migrate into rows that are roughly parallel to the body axis. Grafting experiments have revealed what appears to be a gradient of adhesivity along the wing. What is more, cell adhesivity character is maintained after grafting. Thus we suggest that it is a cell’s location prior to migration that determines its interactions during migration. We use nonlinear bifurcation analysis to show that differential origin-dependent cell adhesion can result in the stabilization of rows over spots.
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    Modeling epithelial cell homeostasis: Steady-state analysis (1999)
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    Bulletin of mathematical biology 61 (1999), S. 1065-1091 
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    Notes: Abstract Critical to epithelial cell viability is the homeostasis of cell volume and composition during changes in transcellular transport. In this study, two previously developed mathematical models (principal cell of the collecting duct and proximal tubule cell) are approximated by their linearizations about a reference condition. This yields matrices which estimate cell volume, cell composition, and transcellular fluxes in response to perturbations of bath conditions and membrane transporter activity. These approximations are themselves extended with the inclusion of linear dependence of membrane transport coefficients on cell variables (e.g., volume, solute concentrations, or electrical potential). This provides cell models with variable permeabilities, which may be homeostatic, and which can be examined systematically: sequentially testing each membrane permeability and its controlling cell variable. In the proximal tubule approximation, volume-mediated increases in peritubular K—Cl or Na—3HCO3 cotransport, and volume-mediated decreases in Na,K-ATPase activity are homeostatic; modulation of peritubular K permeability has little impact. In the principal cell model, volume homeostasis is afforded by volume-sensitive peritubular Na/H exchange or Cl− conductance. Predictions from the linear analysis are confirmed in the full models. This approach yields a systematic examination of homeostasis in an epithelial model, and identifies candidate control parameters.
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    Th1/Th2 differentiation and cross-regulation (1999)
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    Bulletin of mathematical biology 61 (1999), S. 403-436 
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    Notes: Abstract The T helper (Th) phenotypes, Th1/Th2, are acquired upon interaction of a naive T helper cell and an antigen presenting cell (APC). Naive T helper cells may differentiate into either phenotype, and the actual outcome is determined by the density and avidity of the antigenic determinants presented by the APC, and the APCs inherent costimulatory properties. Until recently it was thought that differentiation is further affected by cytokines. However, Murphy et al. (1996, J. Exp. Med. 183, 901) have demonstrated that the experimental results, formerly interpreted as Th1/Th2 differentiation, in effect comprise an observation of two consecutive processes. (i) An interaction between naive T cells and APC creates a mixture of mature cells irreversibly committed to Th1 or Th2 phenotype. (ii) Subsequent addition of regulatory cytokines, promotes expansion of one phenotype while suppressing the other. The consequent shift in the per culture production of marker cytokines mimics the appearance of a cellular phenotype switch. We present and analyse a mathematical model that extrapolates these experimental facts into systemic behavior during an immune response. Despite the fact that differentiation produces cells of Th1 and Th2 phenotypes with the same receptor specificity, our results indicate that competition for antigenic stimulation, mediated by the APCs, combines with cytokine mediated cross-suppression between phenotypes to yield a response that is eventually dominated by T helper cells that are uniform in both receptor specificity (clonotype) and in cytokine secretion phenotype.
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    A two-dimensional numerical study of spatial pattern formation in interacting Turing systems (1999)
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    Bulletin of mathematical biology 61 (1999), S. 483-505 
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    Notes: Abstract For many years Turing systems have been proposed to account for spatial and spatiotemporal pattern formation in chemistry and biology. We extend the study of Turing systems to investigate the rôle of boundary conditions, domain shape, non-linearities, and coupling of such systems. We show that such modifications lead to a wide variety of patterns that bear a striking resemblance to pigmentation patterns in fish, particularly those involving stripes, spots and transitions between them. Using the Turing system as a metaphor for activator—inhibitor models we conclude that such a mechanism, with the aforementioned modifications, may play a rôle in fish patterning.
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    The effect of heterogeneously-distributed RyR channels on calcium dynamics in cardiac myocytes (1999)
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    Bulletin of mathematical biology 61 (1999), S. 651-681 
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    Notes: Abstract Calcium plays an essential role in excitation-contraction coupling in muscle, and derangements in calcium handling can produce a variety of potentially harmful conditions, especially in cardiac muscle. In cardiac tissue specialized invaginations of the sarcolemma, called T-tubules, penetrate deep into each sarcomere, and depolarization of the SL leads to an influx of calcium through voltage-sensitive channels in the T-tubules that in turn triggers further calcium release from the sarcoplasmic reticulum via ryanodine-sensitive calcium channels. Under certain conditions, such as elevated external Ca2+, cardiac cells can release calcium from the sarcoplasmic reticulum spontaneously, producing a calcium ’spark’ and propagating traveling waves of elevated Ca2+ concentration, without depolarization of the SL (Wier and Blatter, 1991a, Cell Calcium 12, 241–254; Williams, 1993, Cell Calcium 14, 724–735; Cheng et al., 1993a, Science 262, 740–744). However, under normal resting conditions these potentially harmful waves seldom occur. In this paper we investigate the role of the periodic distribution of ryanodine-sensitive channels in determining whether a spark can trigger a wave, using a modification of the kinetic model proposed by Tang and Othmer, 1994b, Biophys. J. 67, 2223–2235, for calcium-induced calcium release. We show that the spatial localization of these channels near the T-tubules has a significant effect on both wave propagation and the onset of oscillations in this system. Spatial localization provides a possible explanation for the differing effects of various experimental protocols on the system’s ability to propagate a traveling wave.
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    Bayesian predictive identification and cumulative classification of bacteria (1999)
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    Bulletin of mathematical biology 61 (1999), S. 85-111 
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    Notes: Abstract In this paper we give a mathematically precise formulation of an old idea in bacterial taxonomy, namely cumulative classification, where the taxonomy is continuously updated and possibly augmented as new strains are identified. Our formulation is based on Bayesian predictive probability distributions. The criterion for founding a new taxon is given a firm theoretical foundation based on prediction and it is given a clear-cut interpretation. We formulate an algorithm for cumulative classification and apply it to a large database of bacteria belonging to the family Enterobacteriaceae. The resulting taxonomy makes microbiological sense.
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    Models of classical conditioning (1999)
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    Bulletin of mathematical biology 61 (1999), S. 33-83 
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    Notes: Abstract Classical conditioning is a basic form of associative learning in the animal kingdom. Many paradigmatic features of classical conditioning appear to be conserved throughout species and phyla and are independent of stimulus nature. This paper presents an analysis of trial-based and real-time models of classical conditioning which are mathematical abstractions of the underlying processing principles. Various models are reviewed and in a formal analysis, their capability of simulating and explaining classical conditioning is investigated. Since every existing model fails to simulate some particular conditioning phenomena and since some modelling approaches are not appropriate for detailed mathematical analysis, new model components will be introduced that overcome most of the weaknesses observed in the other models.
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    Book reviews (1999)
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    Bulletin of mathematical biology 61 (1999), S. 399-401 
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    Threshold parameters and metapopulation persistence (1999)
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    Bulletin of mathematical biology 61 (1999), S. 341-353 
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    Notes: Abstract A method is presented to estimate the minimum viable metapopulation size based on the basic reproductive number R 0 and the expected time to extinction τ E for epidemiological models. We exemplify our approach with two simple deterministic metapopulation models of the patch occupancy type and then proceed to stochastic versions that permit the estimation of the minimum viable metapopulation size.
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    Evolution of migration in a metapopulation (1999)
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    Bulletin of mathematical biology 61 (1999), S. 531-550 
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    Notes: Abstract In this paper a general deterministic discrete-time metapopulation model with a finite number of habitat patches is analysed within the framework of adaptive dynamics. We study a general model and prove analytically that (i) if the resident populations state is a fixed point, then the resident strategy with no migration is an evolutionarily stable strategy, (ii) a mutant population with no migration can invade any resident population in a fixed point state, (iii) in the uniform migration case the strategy not to migrate is attractive under small mutational steps so that selection favours low migration. Some of these results have been previously observed in simulations, but here they are proved analytically in a general case. If the resident population is in a two-cyclic orbit, then the situation is different. In the uniform migration case the invasion behaviour depends both on the type of the residents attractor and the survival probability during migration. If the survival probability during migration is low, then the system evolves towards low migration. If the survival probability is high enough, then evolutionary branching can happen and the system evolves to a situation with several coexisting types. In the case of out-of-phase attractor, evolutionary branching can happen with significantly lower survival probabilities than in the in-phase attractor case. Most results in the two-cyclic case are obtained by numerical simulations. Also, when migration is not uniform we observe in numerical simulations in the two-cyclic orbit case selection for low migration or evolutionary branching depending on the survival probability during migration.
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    Determination of the true intraocular pressure and modulus of elasticity of the human cornea in vivo (1999)
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    Bulletin of mathematical biology 61 (1999), S. 551-572 
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    Notes: Abstract The purpose of this study was to determine the true intraocular pressure and modulus of elasticity of the human cornea in vivo. The cornea was modeled as a shell, and the equations for the deformations of a shell due to applanating and intraocular pressures were combined to model the behavior of the cornea during applanation tonometry. At certain corneal dimensions called the calibration dimensions, the applanating and intraocular pressures are considered to be equal. This relationship was used to determine the modulus of elasticity of the cornea and the relationship between the applanating and intraocular pressures. The true intraocular pressure (IOPT) was found to be related to Goldmann’s applanating pressure (IOPG) as (IOPT = IOPG/K, where K is a correction factor. For the calibration corneal thickness of 0.52 mm, the modulus of elasticity E in MPa of the human cornea was found to be related to the true intraocular pressure IOPT in mmHg as E = 0.0229IOPT. The generalization of the Imbert—Fick law that takes into account the effect of corneal dimensions and stiffness was found to be given by IOPT = 73.5W/(K A), where W is the applanating weight in gf (gram force) and A is the applanated area in mm2. The calculated true intraocular pressure and modulus of elasticity were found to agree with published experimental results. The mathematical model developed may therefore be used to improve results from applanation tonometry and to estimate the mechanical property of the cornea in vivo.
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    A model of survival times for predator populations: The case of the army ants (1999)
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    Bulletin of mathematical biology 61 (1999), S. 469-482 
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    Notes: Abstract We develop a method to estimate the expected time of survival of a predator population as a function of the size of the habitat island on which it lives and the dynamic parameters of the population and its prey. The model may be thought of either as a patch occupancy model for a structured population or as a model of metapopulation type. The method is applied to a keystone predator species, the neotropical army ant Eciton burchelli. Predictions are made as to how many of the islands and habitat islands in and around Gatun Lake in the Panama Canal, most of which were formed when the canal was dug, can be expected to support such a population today, and these are compared with data.
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    Bursting, chaos and birhythmicity originating from self-modulation of the inositol 1,4,5-trisphosphate signal in a model for intracellular Ca2+ oscillations (1999)
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    Bulletin of mathematical biology 61 (1999), S. 507-530 
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    Notes: Abstract We investigate the various types of complex Ca2+ oscillations which can arise in a model based on the mechanism of Ca2+-induced Ca2+ release (CICR), that takes into account the Ca2+-stimulated degradation of inositol 1,4,5-trisphosphate (InsP3) by a 3-kinase. This model was previously proposed in the course of an investigation of plausible mechanisms capable of generating complex Ca2+ oscillations (Borghans et al., 1997). Besides simple periodic behavior, this model for cytosolic Ca2+ oscillations in nonexcitable cells shows complex oscillatory phenomena like bursting or chaos. We show that the model also admits a coexistence between two stable regimes of sustained oscillations (birhythmicity). The occurrence of these various modes of oscillatory behavior is analysed by means of bifurcation diagrams. Complex oscillations are characterized by means of Poincaré sections, power spectra and Lyapounov exponents. The results point to the role of self-modulation of the InsP3 signal by 3-kinase as a possible source for complex temporal patterns in Ca2+ signaling.
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    Dominance orders in animal societies: The self-organization hypothesis revisited (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 727-757 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract In previous papers (Theraulaz et al., 1995; Bonabeau et al., 1996) we suggested, following Hogeweg and Hesper (1983, 1985), that the formation of dominance orders in animal societies could result from a self-organizing process involving a double reinforcement mechanism: winners reinforce their probability of winning and losers reinforce their probability of losing. This assumption, and subsequent models relying on it, were based on empirical data on primitively eusocial wasps (Polistes dominulus). By reanalysing some of the experimental data that was previously thought to be irrelevant, we show that it is impossible to distinguish this assumption from a competing assumption based on preexisting differences among individuals. We propose experiments to help discriminate between the two assumptions and their corresponding models—the self-organization model and the correlational model. We urge other researchers to be cautious when interpreting their dominance data with the ’self-organization mindset’; in particular, ‘winner and loser effects’, which are often considered to give support to the self-organization assumption, are equally consistent with the correlational assumption.
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    URL: http://dx.doi.org/10.1006/bulm.1999.0108
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    Hypoxia and reoxygenation: A pressure for mutant p53 cell selection and tumour progression (1999)
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    Bulletin of mathematical biology 61 (1999), S. 759-778 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Recent findings indicate that in a hypoxic environment, oncogenically transformed cells with a mutant form of the tumour suppressor gene p53 may have a survival advantage over similar cells with wild-type p53. This is because the extent of hypoxia-induced apoptosis has been observed to diminish with the loss of wild-type p53 function in certain cell lines. Hypoxic conditions, common in most solid tumours, may thus provide a physiological pressure to select for cells with mutations in the p53 gene. A new model incorporating cell-specific parameters is proposed here to quantify the survival advantage of mutant or null p53 cells over their wild-type counterparts at any level of oxygen deprivation. Predictions are in good agreement with previous monolayer culture experiments comparing hypoxic survival of null and wild-type p53 cells. By extending the model we are able to investigate the effects of repeated rounds of hypoxia and reoxygenation on a mixture of wild-type and mutant or null p53 cells and determine how many rounds are required before a subpopulation of mutant or null p53 cells overtakes a given population of wild-type p53 cells.
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    Non-standard numerical methods applied to subsurface biobarrier formation models in porous media (1999)
    Springer
    Bulletin of mathematical biology 61 (1999), S. 779-798 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Biofilm forming microbes have complex effects on the flow properties of natural porous media. Subsurface biofilms have the potential for the formation of biobarriers to inhibit contaminant migration in groundwater. Another example of beneficial microbial effects is the biotransformation of organic contaminants to less harmful forms, thereby providing an in situ method for treatment of contaminated groundwater supplies. Mathematical models that describe contaminant transport with biodegradation involve a set of coupled convection-dispersion equations with non-linear reactions. The reactive solute transport equation is one for which numerical solution procedures continue to exhibit significant limitations for certain problems of groundwater hydrology interest. Accurate numerical simulations are crucial to the development of contaminant remediation strategies. A new numerical method is developed for simulation of reactive bacterial transport in porous media. The non-standard numerical approach is based on the ideas of the ‘exact’ time-stepping scheme. It leads to solutions free from the numerical instabilities that arise from incorrect modeling of derivatives and reaction terms. Applications to different biofilm models are examined and numerical results are presented to demonstrate the performance of the proposed new method.
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    Analytic models for the patchy spread of plant disease (1999)
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    Bulletin of mathematical biology 61 (1999), S. 849-874 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Plant epidemiologists have long been concerned with the patchy nature of plant disease epidemics. This paper presents a new analytical model for patchy plant epidemics (and patchy dynamics in general), using a second-order approximation to capture the spatial dynamics in terms of the densities and spatial covariances of healthy and infected hosts. Using these spatial moment equations helps us to explain the dynamic growth of patchiness during the early phase of the epidemic, and how the patchiness feeds back on the growth rate of the epidemic. Both underlying heterogeneity in the host spatial arrangement and dynamically generated heterogeneity in the spatial arrangement of infected plants initially accelerate but later decelerate the epidemic.
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    The pathogenesis of normal pressure hydrocephalus: A theoretical analysis (1999)
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    Bulletin of mathematical biology 61 (1999), S. 875-916 
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    Topics: Biology , Mathematics
    Notes: Abstract Hydrocephalus is an abnormal accumulation of cerebrospinal fluid (CSF) in the cerebral ventricles, usually caused by impaired absorption of the fluid into the bloodstream. Despite obstructed absorption and continued secretion of CSF into the ventricles at a near normal rate, the ventricular CSF pressure (VCSFP) is often normal. We attempt to understand how hydrocephalus can exist with normal VCSFP by exploring the role of the brain parenchyma in absorbing CSF in hydrocephalus. We test three theories: (1) the ventricular wall is impermeable to CSF; (2) ventricular CSF seeps into the parenchyma, from which it is efficiently absorbed; and (3) ventricular CSF seeps into the parenchyma but is absorbed inefficiently. We model the brain as a thick spherical shell consisting of a porous, elastic, solid matrix, containing interstitial fluid and blood. We modify the equations of poroelasticity, which describe flow of fluid through porous solids, to allow for parenchymal absorption. For each of the three theories we calculate the steady state changes in VCSFP and in parenchymal fluid pressure caused by an incremental defect in CSF absorption. We also calculate the steady state changes in fluid content, tissue volume, tissue displacement, and stresses caused by a small increment of VCSFP. We conclude that only the second theory—seepage of CSF with efficient parenchymal absorption—accounts for the clinical features of normal pressure hydrocephalus. These features include sustained ventricular dilatation despite normal VCSFP, increased periventricular fluid content, and localized periventricular white matter damage.
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    A theoretical experimental method to determine the locus of desensitization (1999)
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    Bulletin of mathematical biology 61 (1999), S. 963-986 
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    Topics: Biology , Mathematics
    Notes: Abstract Consider a ligand-gated channel with n agonist binding sites which can undergo desensitization. We present a theoretical experimental procedure for pinpointing the principal receptor state from which there is a transition to the desensitized state. The method is based on the observation that the dependence of the slope of the time constant of desensitization vs agonist concentration, at low concentrations, represents the state from which desensitization occurs. In those receptors where desensitization occurs from the open state (or the one immediately preceding it), the method also enables us to determine the number of binding sites.
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    URL: http://dx.doi.org/10.1006/bulm.1999.0121
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    Diffusively coupled bursters: Effects of cell heterogeneity (1999)
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    Bulletin of mathematical biology 61 (1999), S. 1017-1017 
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    Source: Springer Online Journal Archives 1860-2000
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    URL: http://dx.doi.org/10.1006/bulm.1999.0125
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    Modeling the effects of varicella vaccination programs on the incidence of chickenpox and shingles (1999)
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    Bulletin of mathematical biology 61 (1999), S. 1031-1064 
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    Notes: Abstract Two possible dangers of an extensive varicella vaccination program are more varicella (chickenpox) cases in adults, when the complication rates are higher, and an increase in cases of zoster (shingles). Here an age-structured epidemiologic—demographic model with vaccination is developed for varicella and zoster. Parameters are estimated from epidemiological data. This mathematical and computer simulation model is used to evaluate the effects of varicella vaccination programs. Although the age distribution of varicella cases does shift in the simulations, this does not seem to be a danger because many of the adult cases occur after vaccine-induced immunity wanes, so they are mild varicella cases with fewer complications. In the simulations, zoster incidence increases in the first three decades after initiation of a vaccination program, because people who had varicella in childhood age without boosting, but then it decreases. Thus the simulations validate the second danger of more zoster cases.
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    Optimal strategies and complexity: A theoretical analysis of the anti-predatory behavior of the hare (1999)
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    Bulletin of mathematical biology 61 (1999), S. 829-848 
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    ISSN: 1522-9602
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract Predator—prey relationships involving rabbits and hares are widely studied at a long-term population level, while the short-term ethological interactions between one predator and one prey are less well documented. We use a physiologically-based model of hare behavior, developed in the framework of artificial intelligence studies, to analyse its sophisticated anti-predatory behavior. The hares use to stand to the fox in order to inform it that its potential prey is alerted. The behavior of the hare is characterized by specific standing and flushing distances. We show that both hare survival probability and body condition depend on habitat cover, as well as on the ability of the predator to approach—undetected—a prey. We study two anti-predatory strategies, one based on the maximization of the survival probability and the other on the maximization of the body conditions of the hare. Despite the fact that the two strategies are not independent, they are characterized by quite different behavioral patterns. Field estimates of flushing and standing distances are consistent with survival maximization. There exists an optimal anti-predatory strategy, characterized by a flushing distance of 20 m and a standing distance of 30 m, which is optimal in a large set of environmental conditions with a sharp fitness advantage with respect to suboptimal strategies. These results improve our understanding of the anti-predatory behavior of the hare and lend credibility to the optimality approach in the behavioral analysis, showing that even for complex organisms, characterized by a large network of internal constraints and feedback, it is possible to identify simple optimal strategies with a large potential for selection.
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    A model of cell cycle behavior dominated by kinetics of a pathway stimulated by growth factors (1999)
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    Bulletin of mathematical biology 61 (1999), S. 917-934 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Mathematics
    Notes: Abstract A modified version of a previously developed mathematical model [Obeyesekere et al., Cell Prolif. (1997)] of the G1-phase of the cell cycle is presented. This model describes the regulation of the G1-phase that includes the interactions of the nuclear proteins, RB, cyclin E, cyclin D, cdk2, cdk4 and E2F. The effects of the growth factors on cyclin D synthesis under saturated or unsaturated growth factor conditions are investigated based on this model. The solutions to this model (a system of nonlinear ordinary differential equations) are discussed with respect to existing experiments. Predictions based on mathematical analysis of this model are presented. In particular, results are presented on the existence of two stablesolutions, i. e., bistability within the G1-phase. It is shown that this bistability exists under unsaturated growth factor concentration levels. This phenomenon is very noticeable if the efficiency of the signal transduction, initiated by the growth factors leading to cyclin D synthesis, is low. The biological significance of this result as well as possible experimental designs to test these predictions are presented.
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    GTP cyclohydrolase II and 3,4-dihydroxy-2-butanone 4-phosphate synthase are rate-limiting enzymes in riboflavin synthesis of an industrial Bacillus subtilis strain used for riboflavin production (1999)
    Springer
    Journal of industrial microbiology and biotechnology 22 (1999), S. 1-7 
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    ISSN: 1476-5535
    Keywords: Keywords: Bacillus subtilis; riboflavin; 3,4-dihydroxy-2-butanone 4-phosphate synthase; GTP cyclohydrolase II
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: One of the proteins encoded by the riboflavin operon of Bacillus subtilis, RibA, was identified as the rate limiting enzyme in an industrial riboflavin producing strain. An additional single copy of the ribA gene was introduced into the sacB locus of the riboflavin production strain and was expressed constitutively from the medium strength vegI promoter. This led to improved riboflavin titers and yields of riboflavin on glucose of up to 25%. Both enzymatic activities of RibA, the 3,4-dihydroxy-2-butanone 4-phosphate synthase activity located in the N-terminal half of the protein and the GTP cyclohydrolase II activity of the C-terminal domain, are necessary for the improved riboflavin productivity.
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    Thymol-triggered lysis of Escherichia coli expressing Lactobacillus phage LL-H muramidase (1999)
    Springer
    Journal of industrial microbiology and biotechnology 22 (1999), S. 39-43 
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    ISSN: 1476-5535
    Keywords: Keywords: murein; cell wall hydrolase; phage lysin; thymol-triggered lysis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Effective disruption of Escherichia coli cells is achieved by the intracellularly accumulated recombinant murein hydrolase (Lactobacillus bacteriophage LL-H muramidase) after the addition of 5 mM thymol. Thymol destroys the integrity and electric potential of the cytoplasmic membrane, and as a consequence the muramidase can access and hydrolyze the cell wall murein leading to cell lysis. Lysis occurred within 5 min after the addition of thymol and seemed to be efficient at high culture densities. This lysis method does not require cell harvesting or addition of other cell wall weakening substances or exogenous enzymes. As a cell disruption method, thymol-triggered lysis is as efficient as sonication in the presence of 1% Triton. Furthermore, thymol did not interfere with the purification steps of Mur by expanded bed adsorption chromatography (EBA), suggesting that the lysis method presented here is well suited for large-scale production and purification of intracellular proteins of E. coli.
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    Biotransformation of 1-nitrobenzo[e]pyrene by the fungus Cunninghamella elegans (1999)
    Springer
    Journal of industrial microbiology and biotechnology 22 (1999), S. 52-57 
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    ISSN: 1476-5535
    Keywords: Keywords: nitro-PAHs; metabolism; Cunninghamella elegans; biotransformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Biotransformation of 1-nitrobenzo[e]pyrene (1-nitro-BeP), an environmental pollutant derived from the nitration of a non-carcinogen, benzo[e]pyrene, was studied using the fungus Cunninghamella elegans ATCC 36112. After 72 h incubation, 89% of 1-nitro-[3H]BeP added had been metabolized to two major metabolites. These metabolites were separated by reversed-phase high performance liquid chromatography and identified by 1H NMR, UV-visible, and mass spectral techniques as 1-nitro-6-benzo[e]pyrenylsulfate and 1-nitrobenzo[e]pyrene 6-O-β-glucopyranoside. Comparison of the fungal metabolism patterns of 1-nitro-BeP and BeP indicates that the nitro group at the C-1 position of BeP altered the regioselectivity of metabolism.
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    Commercial riboflavin production by recombinant Bacillus subtilis: down-stream processing and comparison of the composition of riboflavin produced by fermentation or chemical synthesis (1999)
    Springer
    Journal of industrial microbiology and biotechnology 22 (1999), S. 19-26 
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    ISSN: 1476-5535
    Keywords: Keywords: recombinant Bacillus subtilis; riboflavin produced by fermentation; down-stream processing; analytics; registration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A novel process for riboflavin production using a recombinant Bacillus subtilis strain has been developed. Here we describe a down-stream processing procedure to obtain riboflavin qualities having a minimal content of 96% (‘feed-grade’) and 98% (‘food/pharma-grade’) riboflavin, respectively. Compared to riboflavin produced by chemical synthesis, products with improved chemical purity were obtained. All compounds representing more than 0.1% of the final products were identified. Feed-grade riboflavin material ex fermentation contained small amounts of amino acids and amino sugars and the biosynthetic riboflavin precursor dimethyl-ribityl-lumazine. All other side products found were derived from riboflavin, resulted from the purification procedure and were also found in riboflavin obtained by chemical synthesis. The Bacillus-produced riboflavin does not contain DNA. The data presented here were used to obtain product approval for the commercial application in the USA, Japan and the UK.
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    Quantitative sampling of indoor air biomass by signature lipid biomarker analysis (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 80-87 
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    ISSN: 1476-5535
    Keywords: Keywords: airborne bacteria; phospholipid fatty acids; human health
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Exposure to airborne biocontaminants may result in a multitude of health effects and is related to a pronounced increase in adult-onset asthma. Established culture-based procedures for quantifying microbial biomass from airborne environments have severe limitations. Assay of the phospholipid fatty acid (PLFA) components of airborne microorganisms provides a quantitative method to define biomass, community composition and nutritional/physiological activity of the microbial community. By collecting airborne particulate matter from a high volume via filtration, we collected sufficient biomass for quantitative PLFA analysis. Comparing high (filtration) and low (impaction) volume air sampling techniques at 26 locations within the Eastern United States, we determined that PLFA analysis provided a viable alternative to the established but flawed culture-based techniques for measuring airborne microbial biomass and community composition. Compared to the PLFA analysis, the culture techniques underestimated the actual viable airborne biomass present by between one to three orders of magnitude. A case study of a manufacturing plant at which there had been complaints regarding the indoor air quality is presented. Phospholipid fatty acid characterization of the biomass enabled contamination point source determination. In comparison with samples taken outdoors, increases in the relative proportion of trans PLFA, reflecting shifts in the physiological status of viable airborne Gram-negative bacteria, were detected in the indoor air samples at a majority of sampling sites.
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    Thermostability of three α-amylases of Streptomyces sp IMD 2679 (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 96-99 
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    ISSN: 1476-5535
    Keywords: Keywords: Streptomyces sp; α-amylase; thermostability; structure-function; dimerisation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The amylolytic system of Streptomyces sp IMD 2679 is composed of three α-amylases, amylase I, II and III, with temperature maxima of 60, 60–65 and 65°C, respectively. Although each α-amylase displayed higher stability in the pH range 6.0–8.5 than at pH 5.0–5.5, differences in their thermostabilities were more evident as the pH increased from pH 6.0 to 8.5. There was a 14-min difference in half-lives between amylase III, the most thermostable enzyme and amylase II at pH 6.0, and a 46-min difference in the half-lives of amylase III and the least thermostable enzyme, amylase I at pH 6.5. In addition, the α-amylases underwent a pH-dependent monomer-dimer transformation. Increased thermostability of the α-amylases was reflected in the variable contents of amino acids (Arg, His, Ser) responsible for electrostatic interactions, and in the levels of aliphatic and bulky hydrophobic amino acids. There was a two-fold reduction in Cys levels in amylase III relative to amylase I and II.
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    Aerobic batch degradation of phenol using immobilized Pseudomonas putida (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 121-126 
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    ISSN: 1476-5535
    Keywords: Keywords: biodegradation; phenol; Pseudomonas putida; immobilized
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Alginate concentrations between 2 and 4% had little effect on the degradation rate of phenol by alginate-immobilized Pseudomonas putida. Ten-degree shifts from 25°C resulted in approximately 30% slower degradation. Maximal degradation rates were favored at pH 5.5–6.0. The response of degradation rate to increased air flow in the bubble column used was almost linear and an optimal higher than 16 vol vol−1 was indicated, although free cells appeared in the reaction medium above 12 vol vol−1. When the initial phenol concentration was raised, degradation rate was not significantly affected until levels higher than 1200 mg ml−1 where performance was markedly reduced. Increasing the ratio of total bead volume to medium volume gave progressively smaller increases in degradation rate. At a medium volume to total bead volume ratio of 5:1, the maximum degradation rate was 250 mg L−1 h−1.
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    Purification and characterization of the intracellular β-glucosidase from Aureobasidium sp ATCC 20524 (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 160-163 
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    ISSN: 1476-5535
    Keywords: Keywords: β-glucosidase; cellobiase; cellobiose-hydrolysis; Aureobasidium
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: β-Glucosidase hydrolyzing cellobiose was extracted from Aureobasidium sp ATCC 20524 and purified to homogeneity. The molecular mass was estimated to be about 331 kDa. The enzyme contained 26.5% (w/w) carbohydrate. The optimum pH and temperature for the enzyme reaction were pH 4 and 80°C, respectively. The enzyme was stable at a wide range of pH, 2.2–9.8, after 3 h and at 75°C for 15 min. The kinetic parameters were determined. The enzyme was relatively stable against typical organic enzyme inhibitors. The enzyme also hydrolyzed gentiobiose, p-nitrophenyl-β-glucoside and salicin.
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    Cryptococcus nodaensis sp nov, a yeast isolated from soil in Japan that produces a salt-tolerant and thermostable glutaminase (1999)
    Springer
    Journal of industrial microbiology and biotechnology 22 (1999), S. 127-132 
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    ISSN: 1476-5535
    Keywords: Keywords: umami; L-glutamic acid, glutaminase; Cryptococcus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An anamorphic basidiomycetous yeast, which produced a salt-tolerant and thermostable glutaminase, was isolated from soil in Japan and classified in the genus Cryptococcus. Its substrate specificity suggests that this enzyme is an L-glutaminase asparaginase (EC 3.5.1.38). The strain, G60, resembles Cryptococcus laurentii in the taxonomic criteria traditionally employed for yeasts, however it can be distinguished as a separate species based on DNA–DNA reassociation experiments and sequence analysis of the large sub-unit rDNA. Phenotypically, the isolate can be differentiated from C. laurentii by the inability to utilize arbutin as a sole source of carbon. Based on sequence analysis, the strain is related to a group of hymenomycetous yeasts including Bulleromyces albus, Bullera unica, C. laurentii and C. skinneri. The strain, which is formally described as Cryptococcus nodaensis, is industrially important for the formation of the umami taste during production of proteolytic seasonings.
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    Closed ecological systems for space travel and extraterrestrial habitation, (Volume 3) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 216-224 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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    URL: http://dx.doi.org/10.1038/sj.jim.2900634
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    Inhibiting sulfate-reducing bacteria in biofilms by expressing the antimicrobial peptides indolicidin and bactenecin (1999)
    Springer
    Journal of industrial microbiology and biotechnology 22 (1999), S. 167-175 
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    ISSN: 1476-5535
    Keywords: Keywords: engineered biofilms; biocorrosion; sulfate-reducing bacteria
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: To identify novel, less-toxic compounds capable of inhibiting sulfate-reducing bacteria (SRB), Desulfovibrio vulgaris and Desulfovibrio gigas in suspension cultures were exposed to several antimicrobial peptides. The bacterial peptide antimicrobials gramicidin S, gramicidin D, and polymyxin B as well as the cationic peptides indolicidin and bactenecin from bovine neutrophils decreased the viability of both SRB by 90% after a 1-h exposure at concentrations of 25–100 μg ml−1. To reduce corrosion by inhibiting SRB in biofilms, the genes for indolicidin and bactenecin were expressed in Bacillus subtilisBE1500 and B. subtilis WB600 under the control of the constitutive alkaline protease (apr) promoter, and the antimicrobials were secreted into the culture medium using the apr signal sequence. Bactenecin was also synthesized and expressed as a fusion to the pro-region of barnase from Bacillus amyloliquefaciens. Concentrated culture supernatants of B. subtilis BE1500 expressing bactenecin at 3 μg ml−1 decreased the viability of Escherichia coli BK6 by 90% and the reference SRB D. vulgaris by 83% in suspension cultures. B. subtilis BE1500 and B. subtilis WB600 expressing bactenecin in biofilms also inhibited the SRB-induced corrosion of 304 stainless steel six to 12-fold in continuous reactors as evidenced by the lack of change in the impedance spectra (resistance polarization) upon addition of SRB and by the reduction in hydrogen sulfide and iron sulfide in batch fermentations with mild steel. A 36-fold decrease in the population of D. vulgaris in a B. subtilis BE1500 biofilm expressing bactenecin was also observed. This is the first report of an antimicrobial produced in a biofilm for in vivo applications and represents the first application of a beneficial, genetically-engineered biofilm for combating corrosion.
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    Fungal cellulases and the microbial decomposition of cellulosic fabric, (Volume 5) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 225-240 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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    Microbial protein from hydrocarbons, (Volume 12) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 259-269 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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    URL: http://dx.doi.org/10.1038/sj.jim.2900638
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    Anaerobic corrosion; metals and microbes in two worlds, (Volume 16) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 288-297 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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    URL: http://dx.doi.org/10.1038/sj.jim.2900641
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    True short stories in microbiology with surprise endings, (Volume 18) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 315-322 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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    URL: http://dx.doi.org/10.1038/sj.jim.2900645
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    Thermophilic microorganisms in extraction of metals from ores, (Volume 18) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 349-360 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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    URL: http://dx.doi.org/10.1038/sj.jim.2900648
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    Bacterial structure in today’s research, (Volume 19) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 394-399 
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    Source: Springer Online Journal Archives 1860-2000
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    URL: http://dx.doi.org/10.1038/sj.jim.2900652
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    Plasmid mediation of mercury volatilization and methylation by Estuarine bacteria, (Volume 20) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 418-427 
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    Source: Springer Online Journal Archives 1860-2000
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    URL: http://dx.doi.org/10.1038/sj.jim.2900655
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    Molecular biology is finally being exploited—let us count some ways, (Volume 21) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 449-459 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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    URL: http://dx.doi.org/10.1038/sj.jim.2900658
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    Actinomycetes in the family, (Volume 24) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 518-525 
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    Source: Springer Online Journal Archives 1860-2000
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    URL: http://dx.doi.org/10.1038/sj.jim.2900661
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    Feast or famine in the deep sea, (Volume 25) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 540-550 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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    URL: http://dx.doi.org/10.1038/sj.jim.2900664
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    The role of bacterial exopolysaccharides in nature and disease, (Volume 26) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 551-563 
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    Source: Springer Online Journal Archives 1860-2000
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    URL: http://dx.doi.org/10.1038/sj.jim.2900665
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    David Perlman obituary, (Volume 21) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 428-429 
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    Source: Springer Online Journal Archives 1860-2000
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    Preface (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 187-187 
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    Microbial oxidation of n-paraffinic hydrocarbons, (Volume 2) (1999)
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    Journal of industrial microbiology and biotechnology 22 (1999), S. 206-215 
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    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
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    URL: http://dx.doi.org/10.1038/sj.jim.2900633
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    Engineering endoglucanase-secreting strains of ethanologenic Klebsiella oxytoca P2 (1999)
    Springer
    Journal of industrial microbiology and biotechnology 22 (1999), S. 600-607 
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    ISSN: 1476-5535
    Keywords: Keywords: endoglucanase; ethanol; Klebsiella; Erwinia; lignocellulose; biomass
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Klebsiella oxytoca P2 was developed as a biocatalyst for the simultaneous saccharification and fermentation (SSF) of cellulose by chromosomally integrating Zymomonas mobilis genes (pdc, adhB) encoding the ethanol pathway. This strain contains the native ability to transport and metabolize cellobiose, eliminating the need to supplement with β-glucosidase during SSF. To increase the utility of this biocatalyst, we have now chromosomally integrated the celZ gene encoding the primary endoglucanase from Erwinia chrysanthemi. This gene was expressed at high levels by replacing the native promoter with a surrogate promoter derived from Z. mobilis DNA. With the addition of out genes encoding the type II protein secretion system from E. chrysanthemi, over half of the active endoglucanase (EGZ) was secreted into the extracellular environment. The two most active strains, SZ2(pCPP2006) and SZ6(pCPP2006), produced approximately 24 000 IU L−1 of CMCase activity, equivalent to 5% of total cellular protein. Recombinant EGZ partially depolymerized acid-swollen cellulose and allowed the production of small amounts of ethanol by SZ6(pCPP2006) without the addition of fungal cellulase. However, additional endoglucanase activities will be required to complete the depolymerization of cellulose into small soluble products which can be efficiently metabolized to ethanol.
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    Biotin production under limiting growth conditions by Agrobacterium/Rhizobium HK4 transformed with a modified Escherichia coli bio operon (1999)
    Springer
    Journal of industrial microbiology and biotechnology 22 (1999), S. 590-599 
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    ISSN: 1476-5535
    Keywords: Keywords: biotin production; E. coli bio operon; Agrobacterium/Rhizobium HK4; limiting growth conditions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: E. coli biotin (bio) operon was modified to improve biotin production by host cells: (a) the divergently transcribed wild-type bio operon was re-organized into one transcriptional unit; (b) the wild-type bio promoter was replaced with a strong artificial (tac) promoter; (c) a potential stem loop structure between bioD and bioA was removed; and (d) the wild-type bioB ribosomal binding site (RBS) was replaced with an artificial RBS that resulted in improved bioB expression. The effects of the modifications on the bio operon were studied in E. coli by measuring biotin and dethiobiotin production, and bio gene expression with mini-cells and two-dimensional polyacrylamide gel electrophoresis. The modified E. coli bio operon was introduced into a broad host-range plasmid and used to transform Agrobacterium/Rhizobium HK4, which then produced 110 mg L−1 of biotin in a 2-L fermenter, growing on a defined medium with diaminononanoic acid as the starting material. Biotin production was not growth-phase dependent in this strain, and the rate of production remained high under limiting (maintenance) and zero growth conditions.
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    Enhancement of maltose utilisation by Saccharomyces cerevisiae in medium containing fermentable hexoses (1999)
    Springer
    Journal of industrial microbiology and biotechnology 22 (1999), S. 627-632 
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    ISSN: 1476-5535
    Keywords: Keywords: fermentation; maltose metabolism; yeast; baking; distilling; brewing; Saccharomyces cerevisiae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Saccharomyces cerevisiae are unable to maintain high rates of fermentation during transition from catabolism of hexoses to maltose. This phenomenon, termed ‘maltose lag’, presents problems for the baking, brewing and distilling industries, which rely on yeast catabolism of mixtures of hexoses and maltose. Maltose utilisation requires the presence of maltose permease and α-glucosidase (maltase), encoded by MAL genes. Synthesis of these is induced by maltose and repressed by glucose. One strain of baker’s yeast used in this work exhibited a marked maltose lag, whereas a second strain exhibited a shorter lag during conversion from hexose to maltose metabolism. The extent of the lag was linked to the levels of maltose permease and maltase in cells at the time of inoculation into mixed sugar medium. This view is supported by results showing that pulsing yeast with maltose to induce expression of MAL genes prior to inoculation into mixed sugar medium, enhanced sugar fermentation. Maltose pulsing of yeasts could therefore be useful for enhancing some fermentations relevant to baking and other yeast industries.
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    Production of raw-starch digesting amyloglucosidase by Aspergillussp GP-21 in solid state fermentation (1999)
    Springer
    Journal of industrial microbiology and biotechnology 22 (1999), S. 622-626 
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    Keywords: Keywords: amyloglucosidase; glucoamylase; raw starch hydrolysis; Aspergillus; solid state fermentation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Aspergillus sp GP-21 produced a raw-starch digesting amyloglucosidase which showed optimum activity at 65°C and pH 5.0–5.5. At 50°C the enzyme converted about 40% of raw corn starch to glucose within 48 h. Enzyme production was studied in solid state fermentation using wheat bran. Productivity was affected by the level of moisture, incubation temperature and the presence or absence of supplements. Maximum enzyme production was observed at a moisture level of 75% and at 30°C. Enzyme production was stimulated by supplementing wheat bran with 0.25% proteose peptone, 1% trace mineral solution, 0.01% CaCl2 and 0.01% MgSO4.
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    In vitro and in vivo antagonism of pathogenic turfgrass fungi by Streptomyces hygroscopicus strains YCED9 and WYE53 (1999)
    Springer
    Journal of industrial microbiology and biotechnology 23 (1999), S. 641-646 
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    ISSN: 1476-5535
    Keywords: Keywords: Streptomyces hygroscopicus; biocontrol; fungi; turf; thatch
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Disease prevention is a current practice used to minimize fungal diseases of turfgrasses in lawns and golf greens. Prevention is accomplished through fungicide applications, and by periodic thatch removal. During the development of a microbial biodethatch product utilizing the lignocellulose-degrading Streptomyces hygroscopicus strains YCED9 and WYE53, we demonstrated using in vitro plate antagonism bioassays that both strains are antagonists of various turfgrass fungal pathogens. These activities were present when the cultures were growing on thatch, as demonstrated by antifungal antagonism bioassays with culture filtrates. Experiments conducted using a growth chamber demonstrated that a bio-dethatch formulation containing spores of strains YCED9 and WYE53 in a zeolite carrier, provided protection for Kentucky bluegrass seedlings against turfgrass pathogens, including Pythium ultimum, Fusarium oxysporum, Rhizoctonia solani, Sclerotinia homeocarpa, Gaeumannomyces graminis and Microdochium nivale. Results showed that by integrating the use of the S. hygroscopicus YCED9/WYE53 bio-dethatch formulation into routine turf management practices, it should be possible to both minimize thatch build-up while also controlling fungal turfgrass diseases by way of the antifungal biocontrol activity of these strains. This in turn would help control fungal pathogens in turfgrass while minimizing the need for routine chemical fungicide applications.
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    A new xylanase from a Trichoderma harzianum strain (1999)
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    Journal of industrial microbiology and biotechnology 23 (1999), S. 682-685 
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    Keywords: Keywords: Trichoderma; xylan; xylanase; characterization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new xylanase (XYL2) was purified from solid-state cultures of Trichoderma harzianum strain C by ultrafiltration and gel filtration. SDS-PAGE of the xylanase showed an apparent homogeneity and molecular weight of 18 kDa. It had the highest activity at pH 5.0 and 45°C and was stable at 50°C and pH 5.0 up to 4 h xylanase. XYL2 had a low K m with insoluble oat spelt xylan as substrate. Compared to the amino acid composition of xylanases from Trichoderma spp, xylanase XYL2 presented a high content of glutamate/glutamine, phenylalanine and cysteine, and a low content of serine. Xylanase XYL2 improved the delignification and selectivity of unbleached hardwood kraft pulp.
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    Kinetic models for astaxanthin production by high cell density mixotrophic culture of the microalga Haematococcus pluvialis (1999)
    Springer
    Journal of industrial microbiology and biotechnology 23 (1999), S. 691-696 
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    ISSN: 1476-5535
    Keywords: Keywords: Haematococcus pluvialis; mixotrophic culture; light irradiance; astaxanthin production; kinetic model
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: High cell density cultivation of Haematococcus pluvialis for astaxanthin production was carried out in batch and fed-batch modes in 3.7-L bioreactors with stepwise increased light intensity control mode. A high cell density of 2.65 g L−1 (batch culture) or 2.74 g L−1 (fed-batch culture) was obtained, and total astaxanthin production in the fed-batch culture (64.36 mg L−1) was about 20.5% higher than in the batch culture (53.43 mg L−1). An unstructured kinetic model to describe the microalga culture system including cell growth, astaxanthin formation, as well as sodium acetate consumption was proposed. Good agreement was found between the model predictions and experimental data. The models demonstrated that the optimal light intensity for mixotrophic growth of H. pluvialis in batch or fed-batch cultures in a 3.7-L bioreactor was 90–360 μmol m−2 s−1, and that the stepwise increased light intensity mode could be replaced by a constant light intensity mode.
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    Extracellular deoxyribonuclease production by a thermophile, Streptomyces thermonitrificans (1999)
    Springer
    Journal of industrial microbiology and biotechnology 23 (1999), S. 709-712 
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    ISSN: 1476-5535
    Keywords: Keywords: Streptomyces thermonitrificans; thermophilic Streptomyces sp; extracellular DNase; enzyme production; metal ions
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A thermophilic bacterial strain, Streptomyces thermonitrificans, produced high levels of extracellular deoxyribonuclease (DNase) when grown on NBG medium (containing 1% peptone, 0.3% beef extract, 1% glucose and 0.5% NaCl). Maximum DNase activity (140 U ml−1) was obtained, in 24 h, when the culture was grown on modified NBG medium (containing 1.3% beef extract, 1% glucose, 0.5% NaCl and 50 μM Mn2+ at 45°C. The crude enzyme showed higher activity on native DNA than on sonicated and heat denatured DNA. Moreover, addition of Mn2+ in the assay mixture resulted in a significant stimulation (10–15 fold) of the enzyme activity.
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    Comparative stability of ethanol production by Escherichia coliKO11 in batch and chemostat culture (1999)
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    Journal of industrial microbiology and biotechnology 23 (1999), S. 701-708 
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    ISSN: 1476-5535
    Keywords: Keywords: ethanol; recombinant; E. coli KO11; lignocellulosic; chemostat; stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Differing claims regarding the stability of the recombinant ethanologen E. coli KO11 are addressed here in batch and chemostat culture. In repeat batch culture, the organism was stable on glucose, mannose, xylose and galactose for at least three serial transfers, even in the absence of a selective antibiotic. Chemostat cultures on glucose were remarkably stable, but on mannose, xylose and a xylose/glucose mixture, they progressively lost their hyperethanologenicity. On xylose, the loss was irreversible, indicating genetic instability. The loss of hyperethanologenicity was accompanied by the production of high concentrations of acetic acid and by increasing biomass yields, suggesting that the higher ATP yield associated with acetate production may foster the growth of acetate-producing revertant strains. Plate counts on high chloramphenicol-containing medium, whether directly, or following preliminary growth on non-selective medium, were not a reliable indicator of high ethanologenicity during chemostat culture. In batch culture, the organism appeared to retain its promise for ethanol production from lignocellulosics and concerns that antibiotics may need to be included in all media appear unfounded.
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    Survival of Lactobacillus helveticus entrapped in Ca-alginate in relation to water content, storage and rehydration (1999)
    Springer
    Journal of industrial microbiology and biotechnology 23 (1999), S. 79-85 
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    Keywords: Keywords: Ca-alginate entrapped lactobacilli; dehydration; water content; protective solutes; survival
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Lactobacillus helveticus CNRZ 303 entrapped in Ca-alginate gel beads was investigated for improved survival and stability during fluidized-bed drying, storage and rehydration. Addition of protective solutes was very important. Studies of the conditions showed that inactivation of entrapped L. helveticus started when the water content exceeded 0.3–0.4 g H2O (g dry wt)−1 for adonitol, glycerol and reconstituted non fat milk solids (NFSM). With Ringer’s solution (control) and betaine, the fall in viability was evident above 1 g H2O (g dry wt)−1. Drying down to 0.2 g H2O (g dry wt)−1 required the removal of 98.5–98.9% of the water. The best survival rate with the least injured cells among survivors was experienced with adonitol and NFMS, respectively, 71% and 57% (compared to the initial) immediately after dehydration. Adonitol and NFMS were also best for survival during storage. The highest cell recovery was obtained by rehydrating the cells in cheese whey permeate between 20–30°C done at pH 6.0–7.0, satisfying the demands for cell survival, repair and slow swelling (adaptions).
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    Expression of the fusion protein recombinant human granulocyte-macrophage colony stimulating factor and leukemia inhibitory factor in a baculovirus vector system (1999)
    Springer
    Journal of industrial microbiology and biotechnology 23 (1999), S. 103-105 
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    ISSN: 1476-5535
    Keywords: Keywords: GM-CSF; LIF; baculovirus system; transfer vector; gene expression
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A fusion gene coding human granulocyte-macrophage colony stimulating factor (GM-CSF) and leukemia inhibitory factor (LIF) cDNAs was inserted into the transfer vector pSXIVVI+ X3 with the control of Syn and XIV promoters. The Sf9 cells (Spodoptera frugiperda) were co-transfected with the recombinant plasmid and TnNPV DNA (Trichoplusia ni nuclear polyhedrosis virus DNA). The fusion protein recombinant human granulocyte-macrophage colony stimulating factor (GM-CSF) and leukemia inhibitory factor (LIF) could be synthesized in cells infected with recombinant virus at a level of about 23% of their total cellular protein. Activity analysis of the fusion protein in infected cells revealed that it exhibited the dual activities of GM-CSF and LIF. Western blot analysis of the expressed fusion protein in infected larvae showed that the virus-mediated fusion protein, with a molecular weight of ∼35 kDa, is confirmed with immunoreactivity.
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    Preparation of 2-aminomuconate from 2-aminophenol by coupled enzymatic dioxygenation and dehydrogenation reactions (1999)
    Springer
    Journal of industrial microbiology and biotechnology 23 (1999), S. 138-142 
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    ISSN: 1476-5535
    Keywords: Keywords: biocatalysis; 2-aminomuconate; 2-aminophenol; Pseudomonas; dioxygenase; dehydrogenase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: 2-Aminomuconate is an intermediate in the oxidative metabolism of tryptophan in mammals. The compound is not commercially available, and studies of its metabolism have been prevented by the lack of a chemical synthesis and the instability of the molecule. We report here the formation of 2-aminomuconate from 2-aminophenol by the coupled action of 2-aminophenol 1,6-dioxygenase and 2-aminomuconic semialdehyde dehydrogenase from Pseudomonas pseudoalcaligenes JS45, and isolation of the product by anion exchange chromatography. The overall procedure was completed within 3 h with a yield of 62%. The availability of the dicarboxyl α-amino acid provides the basis for investigation of the physiological function of 2-aminomuconate in the neuropathologically significant oxidative metabolism of tryptophan.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/sj.jim.2900705
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  • 95
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    Optimal pH control of batch processes for production of curdlan by Agrobacterium species (1999)
    Springer
    Journal of industrial microbiology and biotechnology 23 (1999), S. 143-148 
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    ISSN: 1476-5535
    Keywords: Keywords: curdlan production; optimal pH profile; batch process
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: We sought an optimal pH profile to maximize curdlan production in a batch fermentation of Agrobacterium species. The optimal pH profile was calculated using a gradient iteration algorithm based on the minimum principle of Pontryagin. The model equations describing cell growth and curdlan production were developed as functions of pH, sucrose concentration, and ammonium concentration, since the specific rates of cell growth and curdlan production were highly influenced by those parameters. The pH profile provided the strategy to shift the culture pH from the optimal growth condition (pH 7.0) to the optimal production one (pH 5.5) at the time of ammonium exhaustion. By applying the optimal pH profile in the batch process, we obtained significant improvement in curdlan production (64 g L−1) compared to that of constant pH operation (36 g L−1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/sj.jim.2900714
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  • 96
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    Investigation of actinomycete diversity in the tropical rainforests of Singapore (1999)
    Springer
    Journal of industrial microbiology and biotechnology 23 (1999), S. 178-187 
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    ISSN: 1476-5535
    Keywords: Keywords: actinomycete diversity; phylogeny; rRNA; tropical rainforest
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Five thousand actinomycetes were isolated from soil samples collected from rainforests in Singapore and the generic identities of these isolates were determined by using a procedure that combined morphological, chemotaxonomic and 16S rDNA sequence-based phylogenetic analyses. Actinomycetes belonging to a total of 36 genera were identified. The most abundant isolates are members of Streptomyces, Micromonospora, Actinoplanes, Actinomadura, Nonomuria, Nocardia and Streptosporangium. By phylogenetic analysis of 16S rDNA sequences of our isolates together with those of known actinomycete species, we also evaluated the species diversity of several genera including Streptomyces, Micromonospora, Nonomuria, and Actinomadura. We found that: first, the tropical isolates are present in most clades represented by known species; and second, many tropical isolates form new clades distant from the known species, indicating the presence of unidentified taxa at both species and genus levels. Based on these results, we conclude that actinomycete diversity in the tropical rainforest is very great and should represent an excellent source for discovery of novel bioactive compounds.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/sj.jim.2900723
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  • 97
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    Influence of antagonist, host fruit and pathogen on the biological control of postharvest fungal diseases by yeasts (1999)
    Springer
    Journal of industrial microbiology and biotechnology 23 (1999), S. 223-229 
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    ISSN: 1476-5535
    Keywords: Keywords: biological control; postharvest diseases; yeasts; fruits; biofungicide
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The yeasts Rhodotorula glutinis (LS-11), Cryptococcus laurentii (LS-28), Candida famata (21-D) and Pichia guilliermondii (29-A) and the yeast-like fungus Aureobasidium pullulans (LS-30), previously selected and characterized for mechanisms of action and antagonistic activity against postharvest pathogens in small and large-scale experiments, were used in this study in order to assess interrelationships among the main factors (antagonist, host fruit and fungal pathogen) involved in biological control of postharvest diseases. The antagonists were evaluated for their inhibitory activity (IA) against six common postharvest fungal pathogens on six different host fruits. Artificially wounded fruits were first inoculated with the antagonist and 2 h later with the pathogen; subsequently they were kept at 20°C for 4–6 days. The IA of each antagonist was evaluated and data were submitted to factorial analysis of variance. The populations of antagonists were also monitored on wounded and unwounded fruits kept at 20°C for 7 days. Each factor examined (antagonist, host fruit and fungal pathogen) as well as their interactions significantly affected the IA. However, among the antagonists, isolates LS-28 and LS-30 were only slightly affected by both host and pathogen, showing a wide range of activity, whereas isolate LS-11 had a variable IA. All the antagonists rapidly colonized the wounds, while their population remained substantially unchanged on unwounded fruits. These results suggest that in order to select yeasts with a broad spectrum of action, more suitable for commercial development, it would be advantageous to perform preliminary assays against several pathogens and in particular on different fruit species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/sj.jim.2900727
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  • 98
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    Evaluation of rheological properties of the exopolysaccharide of Sphingomonas paucimobilis GS-1 for application in oil exploration (1999)
    Springer
    Journal of industrial microbiology and biotechnology 23 (1999), S. 442-445 
    Details
    ISSN: 1476-5535
    Keywords: Keywords: Sphingomonas paucimobilis GS-1 exopolysaccharide; rheological properties; biopolymer; drilling fluid; oil exploration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Analysis of an exopolysaccharide of Sphingomonas paucimobilis GS-1 (EPS/GS-1) with respect to its rheological properties, cross-linking ability with chrome alum and performance test at 75 ± 5°C revealed its strong suspending ability, shear thinning property, and thixotrophic nature which are required to impart desirable rheology to drilling mud. The organism fulfilled all the specified requirements and its properties were superior to those of currently-used XC polymer (a xanthan product) for oil drilling applications. However, EPS/GS-1 was unstable in the presence of bentonite at 100 ± 5°C during performance tests, in contrast to XC polymer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/sj.jim.2900737
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  • 99
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    Antagonistic activity of Staphylococcus siderophores and chemical biocides against Bacillus subtilis in a paper-machine environment (1999)
    Springer
    Journal of industrial microbiology and biotechnology 22 (1999), S. 27-32 
    Details
    ISSN: 1476-5535
    Keywords: Keywords: Bacillus; siderophores; antimicrobial; biocides; white water; paper- and boardmachine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The antagonistic potential of nonpathogenic Staphylococcus strains against Bacillus subtilis wild and type strains were studied under conditions simulating a paper- and board-machine environment. The antimicrobial activity was measured by growth inhibition in an automated turbidimeter. The antagonistic potential was compared with that of generally used chemical biocides in a paper- and board-machine environment. The siderophore-containing extracts of Staphylococcus strains significantly inhibited vegetative growth of B. subtilis and delayed the germination of spores both in synthetic and in white-water media. The mill strains were more resistant than type strain against Staphylococcus siderophores and against chemical biocides. The Staphylococcus siderophore-containing extracts did not interfere with the bacteriostatic effect of chemical biocides, but no synergy was detected. The results indicate the potential for application of Staphylococcus siderophore-containing extracts as biocontrol agents in paper- and boardmachine environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/sj.jim.2900596
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  • 100
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    Shear stress effects on plant cell suspension cultures in a rotating wall vessel bioreactor (1999)
    Springer
    Journal of industrial microbiology and biotechnology 22 (1999), S. 44-47 
    Details
    ISSN: 1476-5535
    Keywords: Keywords: RWV; shear; Taxol®; Taxus; secondary metabolite; plant cell culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A rotating wall vessel, designed for growth of mammalian cells under microgravity, was used to study shear effects on Taxus cuspidata plant suspension cell cultures. Shear stress, as quantified by defined shear fields of Couette viscometers, improved specific cell growth rates and was detrimental to volumetric product formation rates.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/sj.jim.2900600
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