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  • 1
    Electronic Resource
    Electronic Resource
    Comparison between in vivo and in vitro enzyme activities in continuous and batch fermentations of Clostridium acetobutylicum (1989)
    Springer
    Applied microbiology and biotechnology 30 (1989), S. 585-595 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary In vitro activities of key enzymes and related parameters (ATP and ADP concentrations, intracellular pH (pH i ), cell volume and the transmembrane ΔpH) in various continuous and batch fermentations of Clostridium acetobutylicum were studied in order to investigate the regulation (genetic vs. enzyme level) of the solventogenesis process. In vitro activities varied significantly among an acidogenic (glucose limited) and three solventogenic (an iron limited, a CO gassed and a biomass recycle) continuous fermentations. However, in vitro enzyme activities did not correlate with in vivo specific production rates in continuous cultures indicating that solvent formation is regulated primarily at the enzyme level. Carbon monoxide (CO) gassing of an acidogenic continuous culture resulted in butyrate uptake without acetone formation due to inactivation of the acetoacetate decarboxylase by CO. In continuous, and to some extent in batch cultures, butyrate can be taken up via the reversal of the butyrate kinase and phosphotransbutyrylase pathway. Solvent formation in batch fermentations is both a result of enzyme induction and regulation. Acetone formation and the induction of acetoacetate decarboxylase occur simultaneously whereas both alcohol dehydrogenases are induced several hours before initiation of alcohol production. Finally, the levels of intracellular and related cell parameters (pH i , ΔpH, ATP and ADP concentrations) are discussed and related to the possible mechanisms of solventogenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00255364
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  • 2
    Electronic Resource
    Electronic Resource
    Enzymes limiting butanol and acetone formation in continuous and batch cultures of Clostridium acetobutylicum (1989)
    Springer
    Applied microbiology and biotechnology 31 (1989), S. 435-444 
    Details
    ISSN: 1432-0614
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary The formation of butanol in continuous cultures of Clostridium acetobutylicum is regulated at the genetic level via expression of butyraldehyde dehydrogenase since increased in vitro activities of this key enzyme are associated with increased in vivo butanol formation rates in both acidogenic and solventogenic fermentations. Addition of glucose, butyric acid and carbon monoxide results in induction of butyraldehyde dehydrogenase. The production of acetone in continuous fermentation is also controlled at the genetic level through expression of coenzyme A (CoA)-transferase; this enzyme is induced by glucose. Carbon monoxide inactivates acetoacetate decarboxylase. In controlled-pH batch fermentation solventogenesis does not correlate with in vitro activities of butyraldehyde dehydrogenase. Instead, initiation of alcohol formation is accompanied by increased activities of both reduced nicotine adenine dinucleotide (NADH)- and reduced nicotine adenine dinucleotide phosphate (NADPH)-specific alcohol dehydrogenases. The production of acetone in batch fermentation is regulated at the genetic level through combined induction of both CoA-transferase and acetoacetate decarboxylase. These two enzymes are not detected in either batch or continuous culture at or above pH 6.0. This finding explains the inability of the cells to produce acetone at elevated culture pH.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00270772
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Solventogenesis in Clostridium acetobutylicum fermentations related to carboxylic acid and proton concentrations (1988)
    New York, NY [u.a.] : Wiley-Blackwell
    Biotechnology and Bioengineering 32 (1988), S. 843-852 
    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 mechanism primarily implicated in the solventogenesis process in batch fermentations of Clostridium acetobutylicum is examined in considerable detail. A variety of fermentations with or without pH control in the pH range of 3.7-6 have been carried out in order to examine which of a host of suspect parameters correlate with the initiation of solventogenesis. The parameters that did not correlate are the external (pH0) and intracellular (pHi) pH, and ΔpH, and the external or intracellular butyrate and acetate concentrations. Undissociated butyric acid (UBA) correlated well with the initiation of solventogenesis. A linear relationship between UBA and butanol concentrations was found at the onset of solventogenesis in all fermentations examined. The intercept of this linear relationship was 6-13mM UBA for the pH0 range of 3.7-5 and approximately zero for pH0 at or above 6. The required minimal UBA was interpreted as a dependency of the solventogenesis process on both H+ and butyrate concentrations. Undissociated acetic acid was found not to correlate with the initiation of solventogenesis. Addition of acetoacetate (AA) and propionate enhanced the effect of UBA on the solventogenesis process. The action of a nonmetabolizable (FCCP) and a metabolizable (AA) uncoupler on the ΔpH, pH0, pHi, and solventogenesis were also studied in order to gain further understanding of the solventogenesis mechanism.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bit.260320702
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    Paper (German National Licenses)
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