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  • 2000-2004  (210)
  • 11
    Electronic Resource
    Electronic Resource
    The Effects of Supraoptimal Temperatures on Population Growth and Cortical Patterning in Tetrahymena pyriformis and Tetrahymena thermophila: A Comparison (2001)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 48 (2001), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: . In this investigation, we compare the multiplication rates and morphogenetic responses of the two most studied Tetrahymena species, T. pyriformis and T. thermophila, at supraoptimal temperatures. Although the upper temperature limits differ greatly in the two species, the pattern of growth responses to high temperature is for the most part similar, with some differences in detail. The transient recovery of cell division at the highest temperature that allows cell division, characteristic of T. pyriformis, is observed in a less distinct form in T. thermophila. Moreover, there is a remarkable difference in developmental response, with drastic abnormalities in patterning of oral structures during the transient recovery of cell division in T. pyriformis, and far more limited abnormalities under similar conditions in T. thermophila. The abnormalities result from spatial disorder in the alignment and orientation of basal body pairs within the early oral primordium, followed by failures in the realignment that normally occurs as oral structures (membranelles and undulating membrane) mature. Both the initial spatial disorder and the failures in realignment are far more severe in T. pyriformis than in T. thermophila.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.2001.tb00296.x
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  • 12
    Electronic Resource
    Electronic Resource
    Effects of trailing jet instability on vortex ring formation (2000)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 12 (2000), S. 589-596 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Numerical simulations of an impulsively started jet were performed in order to investigate the effects of trailing jet instability on axisymmetric vortex ring formation. The predictions were compared to experimental results reported in the literature and to recently published numerical results. The total and vortex ring circulations were found to be in good agreement with both the experimental and the numerical results. The presence of a universal formation time scale was confirmed. The results also highlighted an important interaction between an instability which develops in the trailing jet for large discharge times and the dynamics of the head vortex ring. This interaction accelerates the process by which the vortex ring detaches from the trailing jet and has a significant effect on the vortex ring circulation. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870264
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  • 13
    Electronic Resource
    Electronic Resource
    Numerical simulations of sound radiated from an axisymmetric premixed reacting jet (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 13 (2001), S. 2671-2681 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The sound radiated by an axisymmetric (two-dimensional) premixed reacting free jet was studied using direct numerical simulation. The jet was injected into cold combustion products. A narrow (in radial extent) high temperature pulse was specified at the jet inlet to stabilize the reacting jet. The computational domain included both the near-field flow and far-field acoustic regions. Both reacting and nonreacting cases were considered. The heat release associated with the reacting jet had a significant effect on the vortical structure, as well as the sound radiation level and pattern, within the jet. The sound radiation pattern and the source terms in Lighthill's equation were used to identify apparent sound source locations. Within the context of the assumptions of the present simulations, the results showed that the effect of heat release was to: (1) Stabilize the jet, (2) enhance sound radiation levels due to an increase in the entropy source, and (3) shift the frequency of the most unstable mode to lower values, resulting in a broader sound spectrum. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1386940
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  • 14
    Electronic Resource
    Electronic Resource
    Lévy flights: Exact results and asymptotics beyond all orders (2002)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 43 (2002), S. 2670-2689 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: A comprehensive study of the symmetric Lévy stable probability density function is presented. This is performed for orders both less than 2, and greater than 2. The latter class of functions are traditionally neglected because of a failure to satisfy non-negativity. The complete asymptotic expansions of the symmetric Lévy stable densities of order greater than 2 are constructed, and shown to exhibit intricate series of transcendentally small terms—asymptotics beyond all orders. It is demonstrated that the symmetric Lévy stable densities of any arbitrary rational order can be written in terms of generalized hypergeometric functions, and a number of new special cases are given representations in terms of special functions. A link is shown between the symmetric Lévy stable density of order 4, and Pearcey's integral, which is used widely in problems of optical diffraction and wave propagation. This suggests the existence of applications for the symmetric Lévy stable densities of order greater than 2, despite their failure to define a probability density function. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1467095
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  • 15
    Electronic Resource
    Electronic Resource
    Complete asymptotic expansions of the Fermi–Dirac integrals Fp(η)=1/Γ(p+1)∫0∞[εp/(1+eε−η)]dε (2001)
    College Park, Md. : American Institute of Physics (AIP)
    Journal of Mathematical Physics 42 (2001), S. 1860-1868 
    Details
    ISSN: 1089-7658
    Source: AIP Digital Archive
    Topics: Mathematics , Physics
    Notes: The complete asymptotic expansions, that is to say expansions which include any exponentially small terms lying beyond all orders of the asymptotic power series, are calculated for the Fermi–Dirac integrals. We present two methods to accomplish this, the first in the complex plane utilizing Mellin transforms and Hankel's representation of the gamma function, and the second on the real line using the known asymptotic expansions of the confluent hypergeometric functions. The complete expansions of Fp(η) are then used to investigate the effect that these traditionally neglected exponentially small terms have on physical systems. It is shown that for a 2 dimensional nonrelativistic ideal Fermi gas, the subdominant exponentially small series becomes dominant. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1350634
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  • 16
    Electronic Resource
    Electronic Resource
    An Evaluation of Hsp90 as a Mediator of Cortical Patterning in Tetrahymena (2001)
    Oxford, UK : Blackwell Publishing Ltd
    The @journal of eukaryotic microbiology 48 (2001), S. 0 
    Details
    ISSN: 1550-7408
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: . This study asks two questions: 1) whether Hsp90 is involved in the regulation of cortical patterning in Tetrahymena, and 2) if it is, whether specific defects in this regulation can be attributed to functional insufficiency of the Hsp90 molecule. To address question I, we compared the effects of a specific inhibitor of Hsp90, geldanamycin, on population growth and on development of the oral apparatus in two Tetrahymena species, T. pyriformis and T. thermophila. We observed that geldanamycin inhibits population growth in both species at very low concentrations, and that it has far more severe effects on oral patterning in T. pyriformis than in T. thermophila. These effects are parallel to those of high temperature in the same two species, and provide a tentative affirmative answer to the first question. To address question 2, we ascertained the base sequence of the genes that encode the Hsp90 molecules which are induced at high temperatures in both Tetrahymena species, as well as corresponding sequences in Paramecium tetraurelia. Extensive comparative analyses of the deduced amino acid sequences of the Hsp90 molecules of the two Tetrahymena species indicate that on the basis of what we currently know about Hsp90 both proteins are equally likely to be functional. Phylogenetic analyses of Hsp90 amino acid sequences indicate that the two Tetrahymena Hsp90 molecules have undergone a similar number of amino acid substitutions from their most recent common ancestor, with none of these corresponding to any known functionally critical region of the molecule. Thus there is no evidence that the Hsp90 molecule of T. pyriformis is functionally impaired; the flaw in the control of cortical patterning is more likely to be caused by defects in mechanism(s) that mediate the response to Hsp90, as would be expected from the “Hsp90 capacitor” model of Rutherford and Lindquist.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1550-7408.2001.tb00297.x
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  • 17
    Electronic Resource
    Electronic Resource
    ATOC AND OTHER FACTORS AFFECTING THE DISTRIBUTION AND ABUNDANCE OF HUMPBACK WHALES (MEGAPTERA NOVAEANGLIAE) OFF THE NORTH SHORE OF KAUAI (2002)
    Oxford, UK : Blackwell Publishing Ltd
    Marine mammal science 18 (2002), S. 0 
    Details
    ISSN: 1748-7692
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Humpback whale diving behavior changes subtly when exposed to signals transmitted from the Acoustic Thermometry of Ocean Climate (ATOC) sound projector located 14 km offshore the island of Kauai. This study considered whether such responses would lead to changes in distribution and abundance. A land-based shore station measured humpback whale locations (scan samples) for both nearshore (〈5 km) and offshore (5–10 km) areas. Control observations were made in 1994 and 1998. In 1998 multipleday blocks with ATOC transmissions were interspersed with multiple-day control blocks without transmissions. Sighting rates were higher in 1998 (ATOC) than in 1994 (control year), probably due to better sighting conditions, but may reflect increased population size. Sighting rates did not differ between control and ATOC conditions in 1998. A seasonal sighting peak was observed in both years. No vessel effect on sighting rate was detected in 1998.There was no effect of ATOC on the distance from the shore station to whales, or the depth of water where pods were located. However, the distribution of whales shifted slightly eastward during the ATOC blocks and the mean distance between the ATOC source and pods was greater during transmissions. Nonetheless, more whales were found close to the source when it was on, suggesting a more variable response rather than simple avoidance, with whales found both closer to, and farther away from, the source during transmissions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1748-7692.2002.tb01064.x
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  • 18
    Electronic Resource
    Electronic Resource
    3D structure of EspA filaments from enteropathogenic Escherichia coli (2003)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 49 (2003), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The type III secretion system (TTSS) is a modular apparatus assembled by many pathogenic Gram-negative bacteria and is designed to translocate proteins through the bacterial cell wall into the eukaryotic host cell. The conserved components of the TTSS comprise stacks of rings spanning the inner and outer bacterial membrane and a narrow, needle-like structure projecting outwards. The TTSS of enteropathogenic E. coli is unique in that one of the translocator proteins, EspA, polymerizes to form an extension to the needle complex which interacts with the host cell. In this study we present the 3D structure of EspA filaments to c. 26 Å resolution determined from electron micrographs of negatively stained preparations by image processing. The structure comprises a helical tube with a diameter of 120 Å enclosing a central channel of 25 Å diameter through which effector proteins may be transported. The subunit arrangement corresponds to a one-start helix with 28 subunits present in five turns of the helix and an axial rise of 4.6 Å per subunit. This is the first report of a 3D structure of a filamentous extension to the TTSS.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2003.03555.x
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  • 19
    Electronic Resource
    Electronic Resource
    CesT is a bivalent enteropathogenic Escherichia coli chaperone required for translocation of both Tir and Map (2003)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 47 (2003), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Map is an enteropathogenic Escherichia coli (EPEC) protein that is translocated into eukaryotic cells by a type III secretion system. Although not required for the induction of attaching and effacing (A/E) lesion formation characteristic of EPEC infection, translocated Map is suggested to disrupt mitochondrial membrane potential, which may impact upon subsequent functions of the organelle such as control of cell death. Before secretion, many effector proteins are maintained in the bacterial cytosol by association with a specific chaperone. In EPEC, chaperones have been identified for the effector proteins translocated intimin receptor (Tir) and EspF, and for the translocator proteins EspB and EspD. In this study, we present evidence that the Tir-specific chaperone, CesT, also performs a chaperone function for Map. Using a combination of biochemical approaches, we demonstrate specific interaction between CesT and Map. Similar to other chaperone–effector pairings, binding is apparent at the amino-terminus of Map and is indicated to proceed by a similar mechanism to CesT:Tir interaction. Map secretion from a cesT mutant strain (SE884) is shown to be reduced and, importantly, its translocation from this strain after infection of HEp-2 cells is almost totally abrogated. Although other chaperones are reported to have a bivalent binding specificity, CesT is the first member of its family that chaperones more than one protein for translocation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2003.03290.x
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  • 20
    Electronic Resource
    Electronic Resource
    Identification of a novel type IV pilus gene cluster required for gastrointestinal colonization of Citrobacter rodentium (2003)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 48 (2003), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Citrobacter rodentium is used as an in vivo model system for clinically significant enteric pathogens such as enterohaemorrhagic Escherichia coli (EHEC) and enteropathogenic E. coli (EPEC). These pathogens all colonize the lumen side of the host gastrointestinal tract via attaching and effacing (A/E) lesion formation. In order to identify genes required for the colonization of A/E-forming pathogens, a library of signature-tagged transposon mutants of C. rodentium was constructed and screened in mice. Of the 576 mutants tested, 14 were attenuated in their ability to colonize the descending colon. Of these, eight mapped to the locus of enterocyte effacement (LEE), which is required for the formation of A/E lesions, underlying the importance of this mechanism for pathogenesis. Another mutant, P5H2, was found to have a transposon insertion in an open reading frame that has strong similarity to type IV pilus nucleotide-binding proteins. The region flanking the transposon insertion was sequenced, identifying a cluster of 12 genes that encode the first described pilus of C. rodentium (named colonization factor Citrobacter, CFC). The proteins encoded by cfc genes have identity to proteins of the type IV COF pilus of enterotoxigenic E. coli (ETEC), the toxin co-regulated pilus of Vibrio cholerae and the bundle-forming pilus of EPEC. A non-polar mutation in cfcI, complementation of this strain with wild-type cfcI and complementation of strain P5H2 with wild-type cfcH confirmed that these genes are required for colonization of the gastrointestinal tract by C. rodentium. Thus, CFC provides a convenient model to study type IV pilus-mediated pathogen–host interactions under physiological conditions in the natural colonic environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.2003.03470.x
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