BACTERIAL FERMENTATIONS 



of the way in which our knowledge of specific aspects of some 

 bacterial fermentations has been arrived at. 



Initial Stages of Carbohydrate Fermentation 



One of the most significant developments in the field of 

 fermentation biochemistry in the past few years has been the rec- 

 ognition of the existence of several nonglycolytic pathways of car- 

 bohydrate breakdown. Some indications of nonglycolytic path- 

 ways were obtained long ago by balance experiments, but only 

 since the application of tracer techniques has the evidence for such 

 pathways become conclusive and generally been recognized. 



Two fermentative bacteria have been shown to use pre- 

 dominantly nonglycolytic pathways, namely Leuconostoc mesen- 

 teroides and Pseudomonas lindneri. 



Leuconostoc mesenteroides catalyzes a so-called heterolactic 

 fermentation of glucose, the main products being equimolar 

 amounts of lactic acid, ethanol, and carbon dioxide. The 

 significant feature of this fermentation, from the point of view 

 of its mechanism, is the constancy in the yields of the three 

 products. In other bacterial fermentations giving the same 

 products, the ratio of lactate to ethanol, for example, varies 

 considerably with pYi and other environmental factors. In the 

 Leuconostoc fermentation, on the contrary, half of the glucose is 

 always converted to lactate and half to ethanol and carbon 

 dioxide. This result is inconsistent with the glycolytic mecha- 

 nism, in which both halves of the glucose molecule are funneled 

 through a common intermediate, pyruvate, which can be 

 converted either to lactate or to ethanol. 



More definitive evidence for a nonglycolytic mechanism of 

 glucose fermentation in Leuconostoc was obtained by Gunsalus 

 and Gibbs (14). They found that the fermentation of glucose- 

 l_Ci4 gives labeled carbon dioxide, and glucose-3,4-C^^ gives 

 carboxyl-labeled lactate and ethanol-l-C^l Their data indicate 

 that the carbon dioxide is derived from glucose carbon 1, the 

 methyl and carbinol groups of ethanol from glucose carbons 2 



75 



