442 PRINCIPLES OF SOIL MICROBIOLOGY 



cellulose-plate method or by adding cellulose, in the form of filter 

 paper, to a medium containing the necessary inorganic salts and a 

 source of nitrogen. Krainsky 45 found that certain pigment-producing 

 species, forming small, spherical spores (Act. melanocyclus and Act. 

 melanosporeus) are particularly active in this connection, forming black 

 or red rings on the paper and causing a decomposition of the cellulose. 

 On the agar plate, clear rings are formed around the colony, due to the 

 decomposition of the cellulose by an exo-enzyme. To study the process 

 quantitatively, a definite amount of filter paper is placed in flasks 

 containing a synthetic nutrient medium, with ammonium salt (using 

 in the case of chloride or sulfate also calcium carbonate so as not to 

 allow the reaction to become too acid, which would prevent the develop- 

 ment of the organism) or nitrate as a source of nitrogen. The paper 



TABLE 35 



Cellulose decomposed in 28 days by a mixture of a cellulose-decomposing and 



denitrifying organism 



* CaC0 3 was added with the ammonium chloride so as to keep the reaction 

 alkaline. 



is allowed to dip partly in the medium, since the actinomyces are 

 aerobic organisms and do not develop readily below the surface of the 

 medium. After a definite period of incubation, the culture is filtered 

 and residual paper washed and weighed. It is necessary to determine 

 the nitrogen content of the washed paper, due to the presence of some 

 of the mycelium of the organism. By allowing 10 per cent as the 

 nitrogen content of the mycelium, the residual cellulose can be readily 

 calculated. The liquid medium is analyzed for the residual inorganic 

 nitrogen and various organic acids. It is found that a definite ratio 

 exists between the amount of cellulose decomposed and nitrogen assimi- 

 lated by the organism. Some of the organisms will decompose the 

 paper to such an extent as to leave transparent mucilaginous strands 



*« Krainsky, 1913-1914 (p. 297). 



