BUTYRIC ACID-BUTANOL FERMENTATIONS 33 



feebly and then only when the medium was supplied with 

 a very high concentration of yeast extract. 



The high yeast extract requirement for the growth of 

 CI. tyrobutyricum on lactate was reminiscent of the similar 

 requirement found earlier with CI. kluyveri. Consequently 

 Bhat and I 12 reinvestigated the substrate requirements of 

 CI. tyrobutyricum (CI. lactoacetophilum) particularly in 

 relation to a possible role of acetate. We found that glucose 

 or pyruvate is readily fermented when supplied alone in a 

 medium containing only the usual nutrients required by 

 butyric acid bacteria. In contrast lactate or glycerol cannot 

 be fermented in such a medium unless a roughly stoichio- 

 metric amount of acetate is also provided. When this is 

 done, lactate or glycerol is fermented almost as readily as 

 glucose. Balance experiments showed that acetate is actu- 

 ally consumed during the fermentation of lactate and is 

 converted to butyrate just as in the CI. kluyveri fermenta- 

 tion of ethanol and acetate. 



A schematic explanation for the necessity of additional 

 acetate in the lactate fermentation is given by the following 

 equations. 



CH3CHOHCOOH + H 2 -^£ CH3COOH + CO2 (3) 



4-4H 



2CH2COOH — -> CH3CH2CH2COOH + 2H 2 (4) 



CH3CHOHCOOH + CH3COOH — > 



CH 3 CH 2 CH 2 COOH + H 2 (5) 



The oxidation of lactate to acetate (equation 3) makes 

 available four equivalents of hydrogen for the reduction of 

 acetate or its derivations to butyrate. Two moles of acetate 

 are required for reaction 4, whereas only 1 mole of acetate 

 is formed. Therefore, a second mole of acetate must be 

 supplied in the medium as a source of an oxidant so that 



