DECOMPOSITION OF NON-NITROGENOUS ORGANIC MATTER 437 



In view of the fact that certain aerobic bacteria cannot utilize sugars 

 as sources of energy, it still remains to be demonstrated just how the 

 cellulose molecule is decomposed by these organisms. 



Decomposition of cellulose by anaerobic bacteria. The anaerobic 

 decomposition of cellulose results in the formation of organic acids 

 and gases consisting of carbon dioxide and methane or hydrogen. As 

 pointed out above, Omeliansky 3 * found that the formation of methane 

 or hydrogen in the anaerobic process is due to the fact that different 

 organisms are active in either case. When cellulose was decomposed 

 by the methane organism 50 per cent of the substrate was changed to 

 gas (6.5 per cent methane and 43.5 per cent C0 2 ), and 50 per cent into 

 fatty acids (acetic and butyric). When cellulose was decomposed by 

 the hydrogen organism, about 33 per cent of the substrate was changed 

 into gases (4 per cent hydrogen and 29 per cent C0 2 ) and 67 per cent 

 into fatty acids (acetic, butyric, and small quantities of valerianic 

 acid). The decomposition of cellulose is soon stopped by the rapid 

 accumulation of acids unless CaC0 3 is added to keep the medium neu- 

 tral. Even then the process of cellulose decomposition is very slow 

 and it may take months before 5 to 10 grams of filter paper suspended 

 in a liter of medium are fully dissolved. Omeliansky showed that it 

 took the hydrogen organism thirteen months to form the following 

 products from 3.347 grams of cellulose: 



gra m s 



Fatty acids 2.240 



C0 2 0.972 



H 2 0.014 



The loss of 0.121 gram was believed to be due to substances not 

 determined, including valerianic acid, higher alcohols, aromatic sub- 

 stances and dissolved hydrogen. 



The methane organism formed, out of 2 grams of cellulose decom- 

 posed: 



grams 



Fatty acids 1 .022 



C0 2 . 868 



CH< 0.137 



The methane and hydrogen processes go on simultaneously in mixed 

 culture. A convenient apparatus for the study of cellulose decomposi- 

 tion under anaerobic conditions is shown in fig. 23. 



33 Omeliansky, 1904 (p. 191). 



