Chafter IX 



DECOMPOSITION OF PLANT AND ANIMAL 

 RESIDUES 



The ability of actinomycetes to decompose various organic chemical 

 compounds suggests the probable importance of these organisms in the 

 destruction of complex plant and animal materials in nature, especially 

 in soils, water basins, and composts. Most of the investigations upon 

 which these results are based have been carried out by means of pure 

 cultures. The elucidation of the role played by actinomycetes in the 

 decomposition of complex organic compounds under natural conditions 

 must, therefore, be considered as somewhat arbitrary. Generalizations 

 of the function of certain members of a complex microbiological popula- 

 tion on the basis of results obtained with single organisms and pure 

 chemical compounds have often been faulty. This is true particularly 

 of interpolations of decomposition processes of complex organic materials 

 in complex substrates on the basis of results obtained by the use of pure 

 cultures of actinomycetes acting upon pure chemical compounds under 

 artificial conditions, especially in agar or liquid media. The above con- 

 siderations are further complicated bv the fact that the organisms used 

 for decomposition studies are indefinitely or even incorrectly described. 

 Most of the organisms have been designated by the generic name Ac- 

 tinomyces, thus making it impossible to determine the true nature of the 

 organism involved. Because of the extreme variation in the growth 

 conditions of different actinomycetes, results obtained by the use of 

 liquid or agar media in which certain unknown cultures have grown can 

 hardly be applied to the activities of an extensive population of actino- 

 mvcetes growing in a complex substrate in the presence of many bac- 

 teria and fungi, where the organisms are subject to a variety of associa- 

 tive and antagonistic effects. 



Decomposition of Pure Organic Compounds:— In a comparative 

 study of the decomposition of amino acids by different microorganisms, 

 certain cultures of actinomycetes were found (472) to attack glycine 

 and alanine more effectively than did the fungi employed. More abun- 

 dant growth of the actinomycetes was accompanied by greater ammonia 

 production, as shown previously (p. 81). Glutamic acid, however, 

 allowed better growth of the fungi and poorer growth of the bacterium, 

 the actinomyces growth being intermediate. The amount of ammonia 

 liberated was alike for all three organisms. 



