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  • 1
    Electronic Resource
    Electronic Resource
    Mathematical modelling of growth and substrate conversion of Zymomonas mobilis at 30 and 35°C (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 27 (1985), S. 984-995 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Zymomonas mobilis was grown in continuous cultures at 30 and 35°C. The specific substrate consumption rates at 35°C were higher than those at 30°C. An unstructured mathematical model based on the linear equation for substrate consumption provided a statistically adequate description for cultures grown at 35°C but not for cultures grown at 30°C. A structured two-compartment model described growth and substrate consumption well at both temperatures. Some theoretical and practical aspects of the two-compartment model are discussed.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260270709
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  • 2
    Electronic Resource
    Electronic Resource
    Simulation of the growth pattern of a single cell of Escherichia coli under anaerobic conditions (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 27 (1985), S. 1027-1035 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A computer model based on a previous model for aerobic growth of Escherichia coli is described which simulates cell composition, size, and shape; length of C and D periods; cell yields; and the rate of product formation of anaerobically grown cells of E. coli B/r-A on glucose-limited minimal medium. To verify the simulation results, the values of cell volume, cell content of DNA, RNA, and protein, substrate yield, ATP yield, and fermentation products for various growth rates were obtained experimentally. Model predictions are in good agreement with experimental results. Such agreement supports a hypothesis that only those equations describing energy metabolism need to be modified and other cell functions are not grossly altered by a switch from aerobic to an aerobic growth. The model's ability to predict reasonable growth responses under anaerobic conditions by only modifying energy metabolism is a further indication of the robust nature of the description of cell physiology included in the development of the aerobic model.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260270714
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  • 3
    Electronic Resource
    Electronic Resource
    Simulation of CFSTR through development of a mathematical model for anaerobic growth of Escherichia coli cell population (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 27 (1985), S. 1051-1055 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A computer model is described that simulates a population of Escherichia coli B/r-A cells growing under anaerobic conditions. This population model is an ensemble of single-cell models. The ability of the model of predict the dynamic response of a cell population in a CFSTR to a change in feed flowrates or concentrations was investigated. With glucose as the limiting nutrient the feed concentration of glucose was shifted from 1.0 to 1.88 g/L. With a fixed concentration of glucose (1.0 g/L) step changes in residence time (4.1-1.95 h) were examined. The predicted changes of cell size distribution, substrate concentration, RNA content, and cell dry weight during the transition period compared reasonably well to those observed experiementally. We believe this model is the only model currently available that can make such predictions on an a priori basis.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260270717
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  • 4
    Electronic Resource
    Electronic Resource
    Effect of cycling on final mixed culture fate (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 29 (1987), S. 672-678 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Cycling in feed substrate concentration and dilution rate is examined as a means of modifying the final fate of a mixed culture. It is shown for the case where the specific growth rate of one species is always greater than that of the second that no cycling strategy will provide the desired extinction of the faster growing species unless time delay is included in the modeling. To account for the time lag in adjusting organism metabolic activities to environmental changes, an adaptability parameter is introduced. Numerical simulations are carried out and an operating diagram indicating the conditions under which the desired extinction occurs is constructed. Cycling in feed substrate concentration and dilution rate are both found to produce the desired result.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260290603
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  • 5
    Electronic Resource
    Electronic Resource
    Molecular regulation of methanol oxidase activity in continuous cultures of Hansenula polymorpha (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 32 (1988), S. 577-583 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The regulation of methanol oxidase (MOX) in Hansenula polymorpha has been studied in continuous cultures using a mixture of glucose and methanol (4:1 w/w) as carbon source. The study focused on the identification of stages in the biosynthesis affecting the formation of active MOX in glucose-methanol-grown cells. The levels of MOX mRNA, MOX protein in monomeric and octameric from, the ratio FAD/MOX, and the actual MOX activity have been quantified as functions of the dilution rate D. Hybridization studies with MOX mRNA probes showed an induction of MOX mRNA formation up to D = 0.29 h-1. The induction of MOX protein synthesis (up to 37% of the cellular protein) is determined at low D values on the transcriptional level. The MOX activity at high D values is tuned by FAD incorporation and (post-) translation. Despite the high levels of MOX mRNA, decreasing levels of MOX activity and MOX protein were found at D values ranging from 0.14 t 0.29 h-1. The maximal ratio FAD/MOX(6) was determined at D = 0.1 h-1, which correlated with the maximal specific activity of MOX. In glucose-methanol media both protein level and MOX activity are repressed by increasing levels of residual glucose at high D values.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260320502
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  • 6
    Electronic Resource
    Electronic Resource
    Mathematical modeling of growth and production of alcohol oxidase by Hansenula polymorpha grown on methanol-glucose mixtures (1989)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 33 (1989), S. 524-535 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The modeling of growth and production of methanol oxidase (MOX) by Hansenula polymorpha CBS 4732 has been studied to provide a mathematical description of such production processes. Two kinds of mathematical models were constructed for growth on methanol and on mixtures of methanol and glucose. The model for growth on methanol as the sole carbon source consists of kinetics expressions, a limited number of key steps incorporating substrate and production inhibition. This model was used to predict and simulate the culture dynamics at the start-up, the most critical step in continuous cultivation. The growth on mixtures of methanol and glucose was modeled assuming virtually independent metabolic pathways. The induction and production of MOX could be described by adaptation of various repression equations for various data from the literature. The models describe both experimental data and literature data on growth of H. polymorpha CBS 4732 on glucose-methanol mixtures satisfactorily. All parameters for the induction-repression model for growth of H. polymorpha CBS 4732 on glucose-methanol mixtures yielded evidence that a similar induction-repression pattern is involved in MOX production. Catalase, however, is repressed by a different mechanism.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260330503
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  • 7
    Electronic Resource
    Electronic Resource
    Fermentation kinetics of Zymomonas mobilis near zero growth rate (1987)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 29 (1987), S. 502-512 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The fermentation kinetics Zymomonas mobilis were studied near zero growth rate in fed-batch cultures and continuous cultures with complete cell recycle. The results show the ethanol enhances that specific substrate conversion rate under these conditions. The maximum achievable ethanol concentration in continuous cultures with cell recycle (66 g/L) was significantly lower than in fed-batch cultures (100 g/L). The results indicate that growth-rate-independent metabolism is not instantaneous and can lag behind steadily increasing ethanol concentrations in fed-batch fermentations. A model is proposed to account for this slow adaptation.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260290415
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  • 8
    Electronic Resource
    Electronic Resource
    Effect of cycling on the stability of plasmid-bearing microorganisms in continuous culture (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 31 (1988), S. 464-469 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The implication of the possible existence of differences in the times required for plasmid-bearing and non-plasmid-bearing microorganisms to adjust their metabolic activities to step changes in their environment is examined. This adaptability difference suggests the possibility of maintaining an engineered strain in continuous culture by transient operation. It is shown for the case where adaptability is neglected that no cycling strategy will prevent the washout of the engineered strain, but the addition to the model of a time delay in substrate utilization can result in coexistence upon cycling. Numerical simulations of cycling in feed substrate concentration are carried out to illustrate the concept Operating diagrams are also constructed to indicate the conditions under which washout of the plasmid bearing strain can be prevented.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260310511
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  • 9
    Electronic Resource
    Electronic Resource
    A computer model for the growth and differentiation of a fungal colony on solid substrate (1986)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 28 (1986), S. 405-416 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Mold growth and differentiation are closely related to the formation of secondary products. In solid-substrate fermentations this interrelationship is often more completely realized than in submerged cultures. Solid substrate reactions are used commercially in a limited manner in the western world, but are relatively common in Asia. Basic studies in solid-substrate fermentation should yield results applicable to all types of commercial mold fermentations for the production of a secondary product. This paper presents a relatively simple model for the growth of a mold colony on a solid surface with a defined medium utilizing glucose. Unlike submerged cultures the model must account for both cellular differentiation and the spatial heterogeneity in the system. Model parameters were estimated independently using literature values. The results of the simulation studies suggest that mass transfer limitations are at least partially responsible for the proliferation of differentiated structures on solid substrates as compared to liquid cultures. Since the concentration profile depends on the depth of the substratum, conditions that enhance conidia production can be achieved by controlling the depth of the solid medium.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260280314
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  • 10
    Electronic Resource
    Electronic Resource
    Design of a system for the control of low dissolved oxygen concentrations: Critical oxygen concentrations for Azotobacter vinelandii and Escherichia coli (1985)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 27 (1985), S. 151-155 
    Details
    ISSN: 0006-3592
    Keywords: Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The physiological activity of microorganisms in environments with low dissolved oxygen concentrations often differs from the metabolic activity of the same cells growing under fully aerobic or anaerobic conditions. This article describes a laboratory-scale system for the control of dissolved oxygen at low levels while maintaining other parameters, such as agitator speed, gas flowrate, position of sparger outlet, and temperature at fixed values. Thus, it is possible to attribute in dilute nonviscous fermentations all physiologic changes solely to changes in dissolved oxygen. Experiments were conducted with Azotobacter vinelandii and Escherichia coli. Critical oxygen concentrations for growth (that value of oxygen allowing growth at 97% of μmax) were measured as 0.35 ± 0.03 mg/L for A. vinelandii and 0.12 ± 0.03 mg/L for E. coli. These values are significantly different from the commonly quoted values for critical oxygen concentrations based on respiration rates. Because of the superior dissolved oxygen control system and an improved experimental protocol preventing CO2 limitation, we believe that the values reported in this work more closely represent reality.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260270208
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