H. A. BARKER 



available concerning the occurrence of this pathway in propionic 

 acid bacteria. 



The glycolytic pathway is probably used as a fermentation 

 mechanism by several bacteria, in addition to E. coli. For 

 example, several reactions of this pathway have been demon- 

 strated with Streptococcus faecalis (24), particularly the formation 

 and decomposition of fructose diphosphate. Clostridium perfringens 

 has been shown to contain the enzyme aldolase, indicative of a 

 glycolytic mechanism (1). With several other bacteria, such as 

 C. thermoaceticum (39), Lactobacillus casei (12), and Butyribacterium 

 rettgeri (25), the distribution patterns of C^"* in products obtained 

 from the fermentation of C^^-labeled glucose indicate a pre- 

 dominantly glycolytic pathway, although this has not yet been 

 verified by critical enzymatic experiments. 



The examples given above demonstrate that at least three 

 different pathways exist for the anaerobic decomposition of 

 glucose to three-carbon compounds by bacteria. There is no 

 reason to believe that these are the only such pathways. Of the 

 many anaerobic bacteria that are known, only a very few have 

 been studied extensively enough so that any definite conclusion 

 can be reached concerning their mechanisms of glucose decom- 

 position. Also virtually nothing is known about the energy- 

 utilizing mechanisms that are associated with nonglycolytic 

 sugar decomposition. Only a good beginning has been made in 

 the study of this fundamental aspect of bacterial fermentations. 



The discovery of several alternate pathways of sugar 

 fermentation and other biochemical processes has had a con- 

 siderable effect on the comparative biochemical point of view. 

 Not long ago, many microbiologists in particular believed that 

 all bacteria are built on essentially the same basic metabolic 

 pattern. The conspicuous differences in fermentation products 

 which were known to exist were thought to be attributable to 

 differences in relative rates of various reactions or to the omission 

 or addition of specific enzymatic steps. The possibility that a 

 given process, such as the conversion of glucose to pyruvate, 

 might occur by more than one mechanism was not seriously 



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