128 TRANSFORMATION OF NITROGEN BY SOIL MICROBES 



The liberation of ammonia from the amino acid molecule takes 

 place according to one of the following reactions : 



CH3CH(NH2)COOH + H2O = CH3CH2OH + CO2 + NH3 



Alanine . Ethyl alcohol 



R R R 



I I I 



H— C— NH2 + H2O -> NHa + H— C— OH -^ CH2OH +CO2 



I Alcohol 



COOH COOH 



Amino acid Hydroxy-acid 



HOOC • CH2 • CH2 • CH(NH2) • COOH + H2 



Glutamic acid 



= HOOCCH2CH2CH3 + CO2 + NH3 



Butyric acid 



The ammonia thus produced may accumulate in the soil, it may 

 be used by higher plants or by various microbes (in the presence 

 of available sources of energy), or it may be changed to nitrate. 

 In the light of what has been stated previously regarding the 

 decomposition of such compounds as carbohydrates and the role 

 of nitrogen in decomposition of plant materials, it is relatively 

 easy to determine whether or not ammonia will be liberated in the 

 decomposition of protein materials and about how much ammonia 

 will appear in the complete decomposition of proteins by any one 

 type of microorganism. The amount of nitrogen liberated as 

 ammonia in protein decomposition may be represented as follows: 



N of /N assimilated by N left as \ 



protein de- — I microorganisms + intermediary 1 = N as NH3 

 composed \ in growth products / 



Since pure proteins contain 15 to 18 per cent of nitrogen, ammo- 

 nia is formed in particularly large amounts in the decomposition 

 of organic compounds rich in proteins. Ammonia is a waste 

 product of the metabolism of microorganisms, and is of no further 

 use to the cells concerned in its formation; it accumulates in the 

 absence of organisms able to oxidize it. In view of the fact, how- 

 ever, that organic substances added to the soil do not consist of 

 pure proteins and frequently the protein part is very small in com- 

 parison with the carbohydrates and other non-nitrogenous con- 

 stituents (as in the case of rye or wheat straw which may contain 

 only 2 per cent protein and 98 per cent of other non-nitrogenous 



