30 BACTERIAL FERMENTATIONS 



mulate in the early stages of the fermentation and then 

 decrease simultaneously with the rapid formation of the 

 solvents. Addition of acetate to a starch fermentation 

 resulted in an almost theoretical increase in the yield of 

 acetone, whereas addition of butyrate increased the yield 

 of butanol. The suggested occurrence of acetoacetate as an 

 intermediate between acetate and acetone was supported by 

 the observation that added acetoacetate was converted to 

 acetone and carbon dioxide. 



Several parts of the 1931 picture were largely speculative. 

 For example, the identity of the postulated C 3 compound 

 was not known. Both methyl glyoxal and pyruvate were sug- 

 gested as possibilities, but definitive evidence foi either was 

 lacking. Also the C 2 precursor of butyrate was not known. 

 It was commonly assumed to be acetaldehyde because the 

 aldol condensation in non-biological systems gave a product 

 which might be converted to butyric acid. However, evi- 

 dence for the occurrence of acetaldehyde as an intermediate 

 in the fermentation was slight; neither added acetaldehyde 

 nor acetaldol increased the yield of butyric acid. The 

 identity of the primary C x compound was also uncertain. 

 It was thought to be either formate or carbon dioxide. 

 Kluyver 4 favored the view that formate was formed first 

 and then decomposed to hydrogen and carbon dioxide, but 

 again the evidence was not conclusive. 



This brief summary indicates some of the uncertainties 

 concerning the chemistry of these fermentations that existed 

 twenty-five years ago. Since that time considerable advances 

 have been made in this field. In the following sections I 

 shall try to review some of these developments and pre- 

 sent the current picture of the chemistry of the butyric 

 acid-butanol fermentations. 



The Role of Acetate. One of the most significant devel- 

 opments in this field was the recognition of the key role of 



