Waksman — 144 — Actinomycetes 



scribed. Because of insufficient recognition of their relative abundance 

 and possible importance, most of these can be omitted from considera- 

 tion at the present time. A detailed listing of such types is found in the 

 latest addition of Bergey's Manual. 



Occurrence of Actinomycetes in Manures and Composts:— Next 



to the soil, composts of stable manures and of other plant residues pre- 

 sent the most extensive source of actinomycetes. Under certain condi- 

 tions, as under proper aeration, rapid decomposition of the organic con- 

 stituents of the manure results, and the temperature rises to 60° C. and 

 above. This is accompanied by such abundant development of actino- 

 mycetes as to virtually replace the rest of the microbiological population 

 and become visible to the naked eye in the form of white or gray masses 

 all through the upper layers of the manure pile. These organisms are 

 largely thermophilic in nature. Hence, a consideration of the actino- 

 myces population of manures and composts must give first consideration 

 to thermophilic forms. A detailed discussion of these organisms has al- 

 ready been presented (p. 97). 



In a recent study of the occurrence of thermophilic actinomycetes 

 in high-temperature composts (459, 487), two general groups, similar 

 to those reported by earlier investigators were observed. These may be 

 said to be represented by members of the genus Streftomyces and by 

 various species of Micromonosfora. 



Soils treated with stable manures also contain large numbers of 

 these organisms. Although the thermophilic actinomycetes grow at 

 50° and 65°C., many of them can also grow readily at 28°C. They 

 are, therefore, not obligate but facultative thermophiles. When cul- 

 tures of thermophilic actinomycetes grown on agar media were added to 

 the soil and kept at room temperature, they died out rapidly. When 

 they were introduced with the thermophilic composts, however, they 

 survived in the soil. When the soil was kept at 28 °C., there was no 

 multiplication of the thermophilic actinomycetes. However, composts 

 of horse manure kept at 50° and 65° developed an extensive and highly 

 characteristic population of thermophilic fungi and actinomycetes, as 

 shown in Table 36. The addition of organic matter to the soil has 

 also a marked favorable effect upon the abundance of thermophilic 

 actinomycetes. 



Occurrence of Actinomycetes in Water Basins:— Although waters 

 in general contain very few actinomycetes, fresh-water lakes and certain 

 river waters may contain a highly characteristic population made up 

 pardy of actinomycetes. Mace was the first to establish the fact that 

 actinomycetes are found in water basins. Nadson extended this work 

 and demonstrated that actinomycetes are found abundantly in lake muds. 

 No attention was paid to the fact, however, that these organisms repre- 

 sent only certain special types which are characteristic of this substrate. 



