32 BACTERIAL FERMENTATIONS 



pound present in yeast autolyzate prepared in a special way. 9 

 The concentration of yeast autolyzate necessary to support 

 moderate growth was so high that it soon became evident 

 that the essential compound probably was not an amino 

 acid or a growth factor. Eventually, by fractionation of the 

 yeast autolyzate the major active component was shown to 

 be acetate. 



Fermentation balance experiments then showed that the 

 energy-yielding process used by CI. kluyveri is a conversion 

 of ethanol and acetate to butyrate and caproate. 10 When 

 acetate is present in excess, butyrate is the main product 

 (equation 1) , whereas when ethanol is in excess the main 

 product is caproate (equation 2) . It may be noted that 



CH3CH2OH + CH3COOH — > 



CH3CH2CH2COOH + H 2 (1) 



2CH3CH2OH + CH3COOH — > 



CH3CH2CH2CH2CH2COOH + 2H 2 (2) 



no ethanol is utilized under the anaerobic conditions suit- 

 able for growth of this organism unless acetate is also sup- 

 plied. These balance experiments demonstrated by direct 

 chemical analysis the conversion of acetate to the C 4 and 

 C 6 fatty acids. 



CI. tyrobutyricum is a species originally isolated by 

 van Beynum and Pette 11 from low-grade silage. It was 

 believed to be responsible for the conversion of lactate to 

 the butyrate which is commonly present in silage that has 

 not developed a sufficiently high acidity to inhibit spoilage 

 organisms. When mixed cultures of CI. tyrobutyricum and 

 other silage bacteria were allowed to grow in a complex 

 medium containing lactate and yeast extract, the organism 

 appeared to be responsible for a vigorous fermentation of 

 lactate. However, pure cultures fermented lactate very 



