BACTERIAL FERMENTATIONS 



considered; the existence of two such pathways appeared 

 superfluous and even unreasonable. Therefore the discovery of 

 various alternative pathways for single processes has required a 

 revision of the concept of a basic metabolic pattern in terms of 

 processes rather than in terms of specific chemical mechanisms. 

 It may also be noted that alternate metabolic pathways 

 provide a useful set of characters for the analysis of phylogenetic 

 relationships among microorganisms. Past attempts to deduce 

 phylogenetic relationships from gross inorphology or fermenta- 

 tion product patterns have not been particularly successful, in 

 part because the numbers of characters available were too 

 restricted. This difficulty at least can be overcome by the 

 comparison of complex metabolic pathways which provide many 

 enzymatic steps linked together in process patterns that probably 

 represent the culmination of long sequences of evolutionary 

 development. 



Butyric Acid Fermentation 



Clostridium kluyveri is a good example of an anaerobic 

 bacterium that has been useful in the study of a fundamental 

 biochemical process, namely, the synthesis of fatty acids (5). 

 This organism was discovered more or less fortuitously while 

 making enrichm.ent cultures for methane-producing bacteria 

 with ethyl alcohol as the sole organic substrate. Examination 

 of the fermentation products in such cultures revealed that 

 butyric and caproic acids were frequently formed in large yields 

 along with acetic acid, and were always associated with the 

 presence of a Clostridium later called C. kluyveri. The formation 

 of these acids from ethyl alcohol provided direct confirmation for 

 the old theory that fatty acids containing an even number of 

 carbon atoms are built up from a C2 compound. 



Further study of the substrate requirements for butyrate 

 synthesis by pure cultures of C. kluyveri demonstrated that both 

 ethanol and acetate are essential for the process, which occurs 

 stoichiometrically according to the equation 

 CH3CH2OH + CH3COOH > CH3CH2CH2COOH + H2O 



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