494 PRINCIPLES OF SOIL MICROBIOLOGY 



medium and presence of available carbohydrates also affect the proc- 

 ess. A large part of the nitrogen may be left in the form of inter- 

 mediary products. Organisms like Asp. niger, which produce large 

 amounts of acid (oxalic and citric) from carbohydrates and even from 

 proteins and which are thus enabled to neutralize the ammonia, ac- 

 cumulate only very small amounts of amino acids in artificial cultures; 

 at the same time appreciable quantities of ammonia are formed in 

 the medium. But when the oxalic acid is neutralized with CaC0 3 , or 

 when the formation of both oxalic acid and ammonia is prevented by 

 means of insufficient aeration, an accumulation of amino acids will 

 take place, as with the other fungi. 64 



When the protein is the only source of carbon during the develop- 

 ment of fungi on the protein media, a definite parallelism is found 

 between the growth of the mycelium and the production of ammonia. 

 Different protein derivatives are not utilized alike and their nitrogen 

 is not liberated alike in the form of ammonia. Asp. niger, for example, 

 grows best with leucine, followed by peptone, asparagine and glycocoll. 

 The difference in the nature of the carbon compounds either accompany- 

 ing the proteins or the protein carbon itself accounts for the difference 

 in the amount of fungus growth and ammonia formation. This is 

 due to the fact that, in the absence of available carbohydrates, the 

 organism uses the protein both as a source of energy and as a source 

 of nitrogen; the amount of nitrogen liberated as ammonia will depend 

 not only upon the nitrogen content of the protein, but largely upon 

 the availability of the carbon; the nitrogen is then either liberated as 

 a waste product, ammonia, or is reassimilated and changed into micro- 

 bial protein. 



McLean and Wilson 65 concluded that fungi, rather than bacteria, 

 are responsible for the large accumulations of ammonia in soil rich in 

 organic nitrogenous substances and that this depends upon the chemical 

 and physical composition of the soil, quality of the organic matter 

 present and presence of soluble phosphates. The period of maximum 

 formation and accumulation of ammonia from protein substances by 



64 Butkewitsch, W. Umwandlung der Eiweissstoffe durch die niederen Pilze 

 im Zusammenhange mit einigen Bedingungen ihrer Entwicklung. Jahrb. wiss. 

 Bot., 38: 147-240. 1903. Ammonia as a product of protein transformation by 

 fungi and conditions of its formation (Russian). Rec. d'articles dedies au Prof. 

 C. Timiriazeff. 1916, 457-499. 



66 McLean, H. C, and Wilson, G. W. Ammonification studies with soil fungi. 

 N. J. Agr. Exp. Sta., Bui. 270. 1914. 



