FERMENTATIONS OF NITROGENOUS COMPOUNDS 63 



Zymobacterium oroticum was isolated from mud by 

 Romberg 13 by enrichment with orotic acid. This organ- 

 ism grows slowly at the expense of orotic acid in a relatively 

 complex medium containing tryptone and yeast extract. 

 It also ferments glucose and several other sugars, but not 

 glutamate or lactate. Zymobacterium oroticum has been 

 isolated only once, so nothing can be said about its natural 

 occurrence. This organism is of special interest because 

 it has been used by Lieberman and Romberg 14 - 15 to eluci- 

 date some of the enzymatic steps in pyrimidine biosynthesis. 



The application of the enrichment culture technique has 

 clearly established the existence of a variety of bacteria 

 capable of fermenting single nitrogenous compounds. Sev- 

 eral of these organisms were not previously known. In 

 general, these bacteria show a considerable specialization 

 for the utilization of one or a few structurally related 

 nitrogenous substrates. This specialization is most highly 

 developed in D. glycinophilus and the purine fermenting 

 Clostridia, and least developed in CI. tetanomorphum, which 

 ferments a number of amino acids and other compounds. 



The substrates mentioned in Table 1 are not the only 

 nitrogenous compounds suitable for the enrichment of 

 anaerobic bacteria. Serine and threonine are readily fer- 

 mented in enrichment cultures, although the species mainly 

 responsible for their decomposition under such conditions 

 have not as yet been identified. We have also observed that 

 leucine, valine, cysteine, aspartate, uracil, and thymine can 

 serve as anaerobic enrichment substrates. Probably still 

 other compounds would also be suitable. Further explora- 

 tion of amino acid, purine, and pyrimidine decomposition 

 by the enrichment culture technique will undoubtedly lead 

 to a better understanding of both the biochemistry and 

 microbiology of fermentative processes. 



Of course, knowledge of amino acid fermentations has 



