BUTYRIC ACID-BUTANOL FERMENTATIONS 31^ 



acetate or acetate derivatives in the formation of butyric 

 acid. The first demonstration that acetate can be a pre- 

 cursor of butyrate and butanol was made by Wood et al. 7 

 They used CI. acetobutylicum to ferment starch in the 

 presence of acetate -1-C 13 and determined the distribution 

 of the C 13 in the products. 



/^ TT ^ n CH 3 C*OOH 

 (C 6 Hn0 5 )n > 



c*o 2 



CH 3 C*OCH 3 



CH 3 G*H2CH 2 C*OOH 



CH 3 C*H2CH2C*H 2 OH 



They found, as was to be expected on the basis of earlier 

 balance studies, that the isotope was present in carbon 

 dioxide and the carbonyl group of acetone. This labeling 

 is consistent with a pathway involving acetoacetate, shown 

 in equation 3 of Fig. 1. The additional finding of C 13 

 equally distributed between the 1 and 3 positions of butyr- 

 ate and butanol was quite unexpected. It necessitated the 

 conclusion that the C 4 compounds also are formed by a con- 

 densation of two molecules of acetate or some compound 

 that is easily formed from acetate. 



At about the same time a role of acetate in butyrate 

 synthesis was established independently by nutritional and 

 fermentation balance experiments carried out with two 

 other butyric acid bacteria, namely CI. kluyveri and CI. 

 tyrobutyricum. 



Clostridium kluyveri is a somewhat atypical butyric acid 

 bacterium, which was isolated from enrichment cultures 

 containing ethanol as the only organic compound. 8 This 

 organism was shown to have unusual substrate require- 

 ments. It could not decompose carbohydrates, amino acids, 

 or even pyruvate, but it grew well with ethanol and a com- 



