72 BACTERIAL FERMENTATIONS 



Glycine Fermentation by Diplococcus glycinophilus. 



The fermentation of glycine 45 proceeds according to equa- 

 tion 5. In addition, a small amount of hydrogen is pro- 



4CH 2 NH 2 COOH + 2H 2 — > 



4NH 3 + 2C0 2 + 3CH 3 COOH (5) 



duced, but since the evolution of hydrogen is readily re- 

 versed by a partial pressure of the gas exceeding one-third 

 of an atmosphere, the formation of hydrogen soon ceases 

 in stationary cultures in which the medium quickly becomes 

 saturated with hydrogen. 



The glycine fermentation presents some interesting prob- 

 lems of intermediary metabolism which so far have been 

 studied only by tracer methods. The results show plainly 

 that the chemistry of glycine decomposition by D. glyci- 

 nophilus is entirely different from that catalyzed by Clos- 

 tridium sporogenes. Since the latter organism reduces 

 glycine to acetate and ammonia, one might expect that the 

 glycine fermentation by D. glycinophilus would consist of 

 a complete oxidation of 1 mole of glycine to carbon dioxide 

 coupled with reduction of 3 moles of glycine to acetate. 

 This possibility was tested by fermenting glycine- 1-C 14 , 

 glycine-2-C 14 , and unlabeled glycine plus C 14 -carbon diox- 

 ide and determining the distribution of isotope in the 

 products. The results show that the carbon dioxide is 

 derived entirely from carboxyl carbon of glycine, whereas 

 both carbons of acetate are derived partly from the meth- 

 ylene carbon of glycine and partly from carbon dioxide. 

 These results exclude both a direct reduction of glycine 

 to acetate and a complete oxidation of glycine to carbon 

 dioxide. They suggest an oxidative conversion of glycine 

 to acetate and carbon dioxide, possibly via serine, coupled 

 with a reduction of carbon dioxide to acetate. 



