248 



THE ACTINOMYCETES, Vol. I 



substances depends on the nitrogen source 

 and on the nature of the organism. On pro- 

 longed incubation of the cultures and proper 

 chemical manipulations, preparations were 

 obtained that showed great similarity to the 

 humic acids occurring in natural soils. Cer- 

 tain amino acids can also give rise to brown 

 substances as a result of the growth of some 

 actinomycetes. 



Pure cultures of an organism belonging to 

 the genus Streptomijces and of the fungus Tri- 

 choderma were found by Waksman to de- 

 compose more peat material than did a com- 

 plex soil microbiological population (Table 

 75) . The amount of decomposition was meas- 

 ured by the amount of CO2 and ammonia 

 formed. The ratio of the carbon decomposed 

 to that of the nitrogen liberated was lower 

 for the pure cultures than for the complex 

 population. This indicated that the pure 

 cultures attacked more of the nitrogenous 

 constituents than did the total soil popula- 

 tion. 



Actinomycetes are thus shown to be ca- 

 pable of decomposing resistant humus ma- 

 terials in the soil and bringing about the lib- 

 eration of the constituent elements essential 

 for plant growth. The nitrogen stored up in 

 the humus is changed to ammonia, which is 

 later oxidized to nitrate. Liming of soil and 

 draining of swampy areas favor the develop- 

 ment of actinomycetes as well as the decom- 

 position of the soil organic matter. This proc- 

 ess is of considerable importance to soil 

 fertility. According to Fousek, an increase 



Table 75 



Decomposition of sedge and reed peat hy 



microorganisms (Waksman and Stevens) 



On the basis of 20 gm of dry peat decomposed for 



28 davs under favorable moisture conditions 



in plant growth is obtained by inoculating 

 actinomycetes into the soil, thereby bringing 

 about increased decomposition of the organic 

 matter. This observation has not been fully 

 confirmed as yet. 



Conn also emphasized the importance of 

 actinomycetes in the decomposition of or- 

 ganic residues in the soil. Colonies of these 

 organisms, mostly streptomycetes, were 

 found developing on plates seeded with soil 

 infusions. They made up 20 per cent of the 

 total number of organisms in cultivated soils 

 and 37.5 per cent of organisms from sod soils. 

 The longer the time during which grass was 

 grown in the soil, the larger was the propor- 

 tion of the actinomycetes to the total popu- 

 lation developing on the plate. A soil con- 

 taining 2,900,000 actinomycetes per gram, 

 when treated with grass roots, gave an in- 

 crease in numbers to 6,000,000 in 2 weeks. 

 Both dead grass roots mixed with the soil 

 and grass growing in the soil were found to 

 have a marked stimulating effect upon the 

 development of these organisms. 



Decomposition of High -temperature 

 Composts 



In the decomposition of plant materials, 

 especially in composts of stable manures 

 and artificial composts, high temperature or 

 thermophilic conditions are attained. Under 

 these conditions, actinomycetes play an 

 eminent part in the decomposition process, 

 as brought out first by Globig, Miehe, and 

 others. It Avas later studied extensively by 

 Waksman, Umbreit, and Cordon, who re- 

 ported that at temperatiu'es of 50 to 65°C, 

 the actinomycetes were highly active in the 

 decomposition processes. Soils receiving 

 stable manure contained an abundant pop- 

 ulation of actinomycetes, notably thermo- 

 philic forms, as illustrated in Figure 96. 

 Waksman and Hutchings found that actino- 

 mycetes may be more active in the break- 

 down of plant constituents in mixed pop- 

 ulations than in pure culture. A similar 



