FERMENTATIONS OF NITROGENOUS COMPOUNDS 73 



Alanine and Threonine Fermentations by Clostridium 



prop/on icu/n. Clostridium propionicum is able to ferment 

 alanine, serine, threonine, lactate, pyruvate, and a:rylate. 45 

 With all these substrates except threonine, the main prod- 

 ucts are acetate, propionate, and carbon dioxide; ammonia 

 is also formed from the amino acides. Equation 6 describes 



3CH 3 CHNH 2 COOH + 2H 2 — > 

 3NH 3 + 2CH3CH2COOH + CH3COOH + CO2 (6) 



the fermentation of alanine. Except for ammonia, these 

 products are the same as those formed by the propionic 

 acid bacteria (genus Propionibacterium) . Despite the simi- 

 larities in the products, a considerable amount of evidence 

 indicates that the chemical reactions in the CI. propionicum 

 and Propionibacterium fermentations are substantially 

 different. Succinate is a characteristic product of the Pro- 

 pionibacterium fermentation, and Whiteley 46 has shown 

 that succinate is converted to succinyl-CoA and then decar- 

 boxylated to propionyl-CoA, the immediate precursor of 

 propionate. Clostridium propionicum on the contrary 

 neither forms nor decarboxylates succinate. 47 Further evi- 

 dence against the participation of succinate is the absence 

 of randomization of the a and ft carbons of lactate during 

 its conversion to propionate. 48 Also Johns 47 has shown that 

 CI. propionicum, unlike the propionic acid bacteria, is 

 unable to incorporate carbon dioxide into propionate. 



Perhaps the first indication of a distinctive pathway of 

 propionate formation in CI. propionicum was provided by 

 the discovery that acrylate is fermented at least as rapidly 

 as alanine or lactate. 45 This led to the suggestion that the 

 latter substrates might be converted by loss of ammonia or 

 water to acrylate, which might then be reduced to pro- 

 pionate as follows: 



