BACTERIAL FERMENTATIONS 



attack a great variety of substrates including carbohydrates, 

 polyalcohols, amino acids, purines, pyrimidines, and many 

 organic acids. Consequently they provide a wide range of 

 specialized catabolic processes for study. 



Fermentation Patterns 



Not all organic compounds are fermentable. The question 

 arises as to why some compounds are utilized by anaerobic 

 bacteria and others are not. No answer is possible in terms of 

 molecular structure because the fermentability of a compound 

 depends both on its structure and on the enzymatic make-up of 

 the organism to which it is offered. A partial answer can be 

 given only in terms of the nature of the reactions which a com- 

 pound can undergo in a particular enzymatic system. 



An essential but not always sufficient requirement for 

 fermentability is that the compound or products derived from 

 it must be able to serve both as a reductant and as an oxidant. 

 Furthermore, the potential difference between the oxidant and 

 reductant systems must be great enough (^0.25 v.) to provide 

 the energy necessary to synthesize the various structural and 

 functional components of the cell from simple molecules. Since 

 most biologically important organic compounds are susceptible 

 to enzymatic oxidation, the more unique requirement for fer- 

 mentability is the formation of a suitable oxidant system. 



The oxidizing and reducing systems of bacterial fermenta- 

 tions are provided in several more or less distinct ways. In the 

 simpler fermentations the substrate itself or a phosphorylated 

 derivative is both oxidized and reduced. Examples of this are 

 the dismutation of pyruvate to lactate, acetate, and carbon 

 dioxide by some lactic acid bacteria, and the fermentation of 

 glycerol by Escherichia freundii, in which the oxidation of glycero- 

 phosphate to dihydroxyacetonephosphate and other subsequent 

 products is coupled with the reduction of glycerol to trimethylene 

 glycol (22). In a few fermentations the substrate is converted 

 to two different compounds, one of which is oxidized and the 



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