476 PRINCIPLES OF SOIL MICROBIOLOGY 



ceded, whether to soluble polypeptide molecules or to amino acids and 

 ammonia. The methods of precipitation are also different for the 

 various proteins and involve differences in procedure. 



The second method enables one to follow the course of protein de- 

 composition by the increase in the amino nitrogen. 12 The great dis- 

 advantage of this method is that the various microorganisms will show 

 different increases of amino nitrogen with the same amount of protein 

 decomposed. This is due to the fact that the different organisms, 

 even decomposing equal amounts of proteins, will transform the in- 

 termediary products with different rapidity. The fungi, for example, 

 will hardly allow any great increase in amino nitrogen, but will rapidly 

 transform the intermediary products to ammonia, especially in the 

 absence of available carbohydrate. In the presence of carbohydrate, 

 the protein will be decomposed only to a limited extent. The bacteria 

 and actinomyces, however, will allow a much greater accumulation of 

 amino-nitrogen and a correspondingly lower accumulation of ammonia. 

 The fact that the amino compounds are only intermediate products 

 and that their accumulation depends on the presence of carbohydrates 

 indicates that, at best, this index can be only approximate. 



The third method has the advantage of measuring a final product 

 and not an intermediate one. The fact that various organisms form 

 ammonia from proteins with various speeds, some breaking down the 

 protein completely and others incompletely, is an outstanding dis- 

 advantage of this method. In the presence of available carbohydrates, 

 the ammonia may also be reassimilated by the organism as a source 

 of nitrogen for the synthesis of its protoplasm, so that a mistaken 

 impression may be had that no protein is decomposed. 



The study of protein decomposition would be incomplete without 

 mentioning the so-called processes of putrefaction, or decomposition 

 of proteins in the absence of oxygen or in the presence of a limited 

 amount of it, with the production of evil smelling gaseous products. 13 

 This subject has been least studied from the point of view of trans- 

 formation in the soil; most of the work was done in connection with 

 pathogenic anaerobic bacteria. Putrefaction was often differentiated 



12 Sears, H. J. Studies in the nitrogen metabolism of bacteria. Jour. Inf. 

 Dis., 19: 105-137. 1916; Itano, A. The relation of hydrogen ion concentration 

 of media to the proteolytic activity of Bacillus subtilis. Mass. Agr. Exp. Sta. 

 Bui. 167. 1916; Waksman, 1918 (p. 495); Debord, J. J. Certain phases of nitrog- 

 enous metabolism in bacterial cultures. Jour. Bact., 8: 7-45. 1923. 



is Fliigge. Die Mikroorganismen. Leipzig. Vogel. 1896. v. I, p. 254. 



