STUDIES ON PROTEOLYTIC ACTIVITIES OF SOIL 

 MICROORGANISMS, WITH SPECIAL REFER- 

 ENCE TO FUNGP 



SELMAN A. WAKSMAN 



From the Department of Biochemistry, University of California 



Received for publication October 19, 1917 

 INTRODUCTION 



It has long been recognized that when organic matter is applied 

 to the soil it must be broken down into certain simple compounds 

 before it can be assimilated by the roots of the plants and built 

 up again into living tissues. This holds true, particularly, with 

 nitrogenous compounds, such as the different proteins found m 

 the plant residues, animal manures, and other protem substances 

 applied to the soil. The plant is unable to assimilate the nitrogen 

 from the complex protein bodies, and the latter must first be 

 decomposed by means of other agencies before the assimilation 

 of the nitrogen by the plant can take place. It is not known 

 whether the organic and mineral acids found in the soil or those 

 possibly excreted by the roots of the plants play any part m 

 the hydrolysis of these proteins. But it is known that the micro- 

 organisms of the soil are able to decompose the protems and hber- 

 ate the nitrogen, which is enclosed in the complex protem mole- 

 cule in a simple form, which, either at once or after undergoing 

 transformation due to the action of other bacteria, is easily 

 assimilable by the roots of higher plants. , . , -i 



A great deal of attention has been paid by the students of soil 

 fertihty to this process of decomposition, which the organic 

 matter undergoes in the soil; it would take up too much space to 



. The data presented in this paper form part I of the dissertation present^^^^^^^^ 

 the author for the degree of Doctor of Philosophy, University of California, 

 December, 1917. 



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