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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied microbiology and biotechnology 35 (1991), S. 1-3 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Ethanol is identified as a strongly inhibitory metabolite in addition to acetic acid and 2,3-butanediol in 2,3-butanediol production by Enterobacter aerogenes. A model is proposed to describe the multiproduct-inhibited growth of E. aerogenes in 2,3-butanediol fermentation. The model is verified with data from anaerobic and microaerobic continuous culture. On the basis of this model the difference in biomass production and product patterns during anaerobic and microaerobic growth of E. aerogenes is discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    Applied microbiology and biotechnology 33 (1990), S. 485-489 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The effect of pH and acetic acid on growth and 2,3-butanediol production of Enterobacter aerogenes from glucose was investigated in a microaerobic continuous culture. At a dilution rate of 0.20 h−1 and a fixed oxygen uptake rate (OUR) of 31.5 mmol l−1 h−1 the biomass concentration increased with pH ranging from 5.0 to 7.0, while the specific ATP requirement of the cells decreased. In the pH range 5.5–6.5 the product concentration (butanediol + acetoin) was maximal and nearly constant. However, the specific production continuously declined with increasing pH. Experiments with addition of acetic acid showed that the various effects of pH are due to inhibition of the by-product acetic acid on cell growth. The strength of the acetic and inhibition depended only on the concentration of its undissociated form [HAc]. The biomass concentration and the specific OUR were also only functions of [HAc], irrespective of the pH. Although the specific ATP requirement (q ATP) strongly depended on the pH, [HAc] at constant pH.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Applied microbiology and biotechnology 33 (1990), S. 264-268 
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The influence of oxygen on growth and production of 2,3-butanediol and acetoin by Enterobacter aerogenes was studied in continuous culture. At all dilution rates (D) studied cell mass increased steadily with increasing oxygen uptake rate (OUR), hence the micro-aerobic cultivation was energy-limited. The biomass yield on oxygen increased with D which suggests that cells need more energy for maintenance functions at lower D. At each D an optimal OUR giving highest volumetric productivity for the sum of butanediol and acetoin was found. The optimal OUR increased with D. The occurrence of optimal OURs results from the various effects of O2 on growth and specific productivity. The latter was found to be a linear function of the specific OUR irrespective of D. At optimal OUR the cells proved to have equal specific OURs and equal specific productivities representing a fixed relationship between fermentative and respiratory metabolism. The product yield based on glucose and corrected for biomass formation was 80%. A product concentration as high as 43 g/l was obtained at D =0.1 h−1 while the volumetric productivity was the highest at D =0.28 h−1 (5.6 g/l and hour). The findings further indicate that growth and product generation are obviously non-associated phenomena. Hence, high productivities may be achievable by cell recycling and cell immobilisation systems.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Biotechnology letters 16 (1994), S. 1103-1106 
    ISSN: 1573-6776
    Source: Springer Online Journal Archives 1860-2000
    Topics: Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The nutrient demand of the pentachlorophenol-degrading bacteriumMycobacterium chlorophenolicum was characterized in shake flask experiments. A minimal medium containing sorbitol as sole carbon and energy source and thiamine as the only organic growth factor was developed that allows satisfactory growth of the strain.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 40 (1992), S. 1078-1084 
    ISSN: 0006-3592
    Keywords: 2,3-butanediol ; microaerobic culture ; TCA cycle ; oxygen utilization ; reactor design ; mixing ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A new parameter, the relative utilization of tricarboxylic acid (TCA) cycle β, is introduced to quantitatively account for the involvement of fermentation pathways and TCA cycle in the utilization of oxygen under oxygen-limiting (microaerobic) conditions. With the facultative anaerobe Enterobacter aerogenes, which produces 2,3-butanediol, a method is proposed to calculate β from measurement of metabolites and exhaust gas. In continuous culture β was found to be small under oxygen limitation, indicating that the fermentation pathways were preferred over the TCA cycle and oxygen was almost entirely consumed through oxidation of reduced nicotinamide adenine dinucleotide (NADH2) released by fermentation under these conditions. The increase of β at high oxygen supply revealed a saturation of oxygen utilization through fermentation pathways. It could be concluded that, for the optimal performance of a microaerobic culture, oxygen uptake rate must be kept at such a level that as much NADH2 as possible from fermentation pathways is oxidized by oxygen, and at the same time the utilization of TCA cycle is kept at a minimum. As the dynamics of the microaerobic culture can be fast, a significant effect of reactor hydrodynamics, i.e., mixing, on the overall performance can be expected. This was confirmed experimentally, and the parameter β proved to be a useful reactor design criterium for the microaerobic cultivation. © 1992 John Wiley & Sons, Inc.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 46 (1995), S. 314-324 
    ISSN: 0006-3592
    Keywords: product formation ; kinetic model ; microbial cells ; mammalian cells ; substrate excess ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Growth of microbial and mammalian cells can be classified into substrate-limited and substrate-sufficient growth according to the relative availability of the substrate (carbon and energy source) and other nutrients. It has been observed for a number of microbial and mammalian cells that the consumption rate of substrate and energy (ATP) is generally higher under substratesufficient conditions than under substrate limitation. Accordingly, the product formation under substrate excess often exhibits different patterns from those under substrate limitation. The extent of increase or decrease in product formation may depend not only on the nature of limitation and cell growth rate but also on the residual substrate concentration in a relatively wide range. The product formation kinetic models existing in literature cannot describe these effects. In this study, the Luedeking-Piret kinetic is extended to include a term describing the effect of residual substrate concentration. The extended model has a similar structure to the kinetic model for substrate and energy consumption rate recently proposed by Zeng and Deckwer. The applicability of the extended model is demonstrated with three microbial cultures for the production of primary metabolites and three hybridoma cell cultures for the production of ammonia and lactic acid over a wide range of substrate concentration. The model describes the product formation in all these cultures satisfactorily. Using this model, the range of residual substrate concentration, in which the product formation is affected, can be quantitatively assessed. © 1995 John Wiley & Sons, Inc.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 50 (1996), S. 238-247 
    ISSN: 0006-3592
    Keywords: hybridomas ; monoclonal antibody ; kinetic model ; instability ; nutrient and product effects ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: An attempt has been made to mathematically describe and analyze monoclonal antibody (MAB) productivity of hybridoma cells, with particular emphasis on continuous cultures under unsteady-state conditions. A simple and unstructured general kinetic model that takes account of productivity loss during long-term cultivation, cell proliferation, and the effects of nutrients and toxic products is proposed. The model is verified with data of continuous culture from five different cell lines under a wide range of experimental conditions. Analysis of these results showed that for a reliable assessment of effects of different factors and for comparison of kinetic data on MAB production it is important to consider possible loss of MAB productivity, the time dependence of which can be modeled by an exponential function plus a constant term. Variations of nutrient concentration, particularly that of glucose, glutamine, and serum, can significantly alter MAB production under certain conditions. These effects can be described in terms of saturation kinetic and/or noncompetitive inhibition kinetics. © 1996 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0006-3592
    Keywords: glycerol fermentation ; Klebsiella pneumoniae ; oscillation ; hysteresis ; growth and metabolism ; substrate excess ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Oscillation and hysteresis phenomena are observed in the anaerobic continuous fermentation of glycerol by Klebsiella pneumoniae in long-term cultivations under a variety of conditions. In this work, the conditions for the occurrence of these phenomena are reported and the patterns of cell growth and metabolism under oscillation are characterized. During an oscillation period, the formation rates of CO2, H2, and formate and the consumption rate of alkali periodically pass values of maxima and minima, the latter being close to zero. The formation of biomass and fermentation products such as 1,3-propanediol, acetate, and ethanol also undergo periodic changes which shift maxima and minima. Sustained oscillation occurs only under conditions of substrate excess within a distinct regime. At pH 7.0, it is only found at dilution rates above 0.15 h-1 under the experimental conditions. At lower pH values, oscillations are more likely to happen, even at a relatively low dilution rate and low substrate excess. Whereas the amplitude of oscillations at pH 7.0 depends on both the dilution rate and the residual glycerol concentration (CGlyc) the interval of oscillations appears to be only a function of CGlyc. An increase of CGlyc in culture damps the oscillation and leads to its disappearance at CGlyc = 1100 to 1200 mmol/L (pH 7.0). The operation mode was also found to be an important parameter in determining the stability and actual state of the culture, resulting in hysteresis under certain conditions, particularly at low pH values. Generally, a large perturbation of cultivation conditions tends to cause oscillation and hysteresis. The results unambiguously demonstrate that the oscillation and hysteresis phenomena shown in this work are bound to genuine metabolic fluctuations of the microorganism. They reveal several differences and new features compared with those reported in the literature and cannot be readily explained by the mechanisms known so far. © 1996 John Wiley & Sons, Inc.
    Additional Material: 10 Ill.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 0006-3592
    Keywords: oscillation ; Klebsiella pneumoniae ; glycerol metabolism ; metabolic fluxes ; pathway analysis ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The oscillation phenomena reported in the preceding article for the anaerobic continuous fermentation of glycerol by Klebsiella pneumoniae are analyzed in terms of metabolic fluxes (metabolic rates and yields) and stoichiometry of pathways. Significant oscillations in the fluxes of CO2, H2, formic acid, ethanol, and reducing equivalents are observed which show obvious relationships to each other. Changes in the consumption or production rates of glycerol, acetic acid, 1,3-propanediol, and ATP are irregular and have relatively small amplitudes compared with their absolute values. By comparing the metabolic fluxes under oscillation and steady state that have nearly the same environmental conditions it could be shown that pyruvate metabolism is the main step affected under oscillation conditions. The specific formation rates of all the products originating from pyruvate metabolism (CO2, H2, formic acid, ethanol, acetic acid, lactic acid, and 2,3-butanediol) show significant differences under conditions of oscillation and steady state. In contrast, the specific rates of substrate uptake, ATP generation, and formation of products deriving either directly from glycerol (1,3-propanediol) or from the upstream of pyruvate metabolism (e.g., succinic acid) are not, or at least not significantly, affected during oscillation. Stoichiometric analysis of metabolic pathways confirms that other enzyme systems, in addition to pyruvate: formate-lyase, must be simultaneously involved in the pyruvate decarboxylation under both oscillation and steady-state conditions. The results strongly suggest oscillations of activities of these enzymes under oscillation conditions. It appears that the reason for the occurrence of oscillation and hysteresis lies in an unstable regulation of pyruvate metabolism of different enzymes triggered by substrate excess and drastic change(s) of environmental conditions. © 1996 John Wiley & Sons, Inc.
    Additional Material: 9 Ill.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 55 (1997), S. 480-489 
    ISSN: 0006-3592
    Keywords: pentachlorophenol ; Mycobacterium chlorophenolicum ; adsorption and desorption ; isotherm model ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The sorption behavior of pentachlorophenol (PCP) by the Gram-positive bacterium Mycobacterium chlorophenolicum PCP-1 was quantitatively characterized in this work, with emphasis on the effects of biomass and pH and on the reversibility of PCP adsorption. Both the adsorption and desorption of PCP showed a fast kinetic, reaching an equilibrium in less than 1.5-min mixing under the experimental conditions. For PCP concentrations up to 600 μmol/L no saturation of the adsorption was observed and the adsorption isotherms can be adequately described by the Freundlich equation. The adsorption capacity (qads) of M. chlorophenolicum PCP-1 increased significantly with decreasing biomass in the low concentration range (below 0.5 g/L). The biomass concentration merely affected the capacity constant K of the Freundlich model while the intensity parameter n remained constant. The qads also increased with decreasing pH, particularly at acidic pH values. Again, the pH effect was mainly reflected by the change of K. Based on these results a correlation for qads, in which K is a function of both biomass concentration and pH, was obtained to describe the adsorption isotherms at different biomass concentrations and pH values. The desorption of PCP was also found to be strongly affected by pH. At pH 5.4 the adsorption was almost completely irreversible, while a nearly complete desorption was obtained at pH 7. The effect of pH on the sorption behavior was found to be related to the ionization of PCP. The irreversibly adsorbed PCP is a strict function of concentration of undissociated PCP, while the reversibly adsorbed PCP correlates well with the concentration of ionic PCP. The irreversible adsorption has a much higher adsorption capacity than the reversible adsorption. These findings led to the derivation of a semimechanistic model that satisfactorily describes the sorption of PCP by M. chlorophenolicum. The results obtained also give clues to the patterns and mechanism(s) of PCP adsorption by microbial cells. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 480-489, 1997.
    Additional Material: 11 Ill.
    Type of Medium: Electronic Resource
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