Waksman — 1 34 — Actinomycetes 



was not recognized for many years. Mace (278) reported, in 1888, 

 that actinomycetes occur abundantly in water basins. Globig (138), 

 in 1888, and Rossi-Doria (370), in 1891, made a detailed study of their 

 occurrence and activities in different soil types. 



In 1900, Beijerinck drew attention to the fact that actinomycetes 

 are widely distributed in nature. They were found not only in the 

 surface layers of the soil but also in the subsoil to considerable depths; 

 at depths of one meter in garden soil and two meters in sandy soils, they 

 sometimes exceeded in numbers the other groups of microorganisms. 

 They were also present in river mud below the river bed. Beijerinck 

 emphasized the fact that actinomycetes represent a group of omni\'orous 

 organisms capable of growing not only under conditions favorable to 

 their development but even under certain unfavorable conditions. He 

 even found them to grow in distilled water in ordinary laborator\' air. 

 They were unable, however, to fix atmospheric nitrogen. 



Nadson (311) also studied in 1900 the occurrence of actinomycetes 

 in nature and their role in natural processes and as geological agents. 

 He isolated several cultures of these organisms from the curative mud of 

 a salt lake, and established their ability to decompose proteins, to pro- 

 duce ammonia and HoS, and precipitate CaCOa. 



Since the work of these pioneers, considerable information has ac- 

 cumulated concerning the abundance of actinomycetes in various na- 

 tural substrates, as determined by cultural and direct microscopic meth- 

 ods. Although great advance has been made in the appreciation of the 

 role of actinomycetes in many natural processes, no clear picture has 

 been drawn of this function of so large and heterogeneous a group of 

 microorganisms, and the information may still be considered as largely 

 fragmentary. This is due largely to a lack of sufficient knowledge con- 

 cerning the intermediary metabolism of actinomycetes, their relationship 

 to other microorganisms growing in natural substrates, and their fre- 

 quent confusion with the bacteria and with the fungi. The last is 

 particularly important, since actinomycetes are capable of bringing about 

 reactions, such as protein decomposition, ammonia formation, nitrate re- 

 duction, and cellulose decomposition, which are commonly associated 

 with activities of fungi and bacteria. 



Occurrence of Actinomycetes in the Soil:— The soil represents an 

 ideal natural substrate for the development of actinomycetes. It is no 

 wonder, then, that they are found so abundantly there, where they are 

 represented by many genera and species. They are found in both virgin 

 and cultivated soils, in fertile and in unfertile soils, in various regions 

 throughout the world (126, 440, 461). They are particularly abundant 

 in alkaline soils and in soils rich in organic matter. It has even been 

 suggested that their major function in the soils consists in the decompo- 

 sition of plant and animal residues (76, 484). 



