THE ACTINOMYCETES, Vol. II 



celium, type of speculation, shape and sur- 

 face of spore), and finally the ecological ap- 

 proach (anaerobic versus aerobic, pathogenic 

 versus nonpathogenic, thermophilic versus 

 mesophilic). The idea of a physiological clas- 

 sification includes formation of antibiotics 

 and of enzymes, utilization of carbon com- 

 pounds, and transformation of nitrogenous 

 compounds, all of which can supply supple- 

 mentary information. 



Speciation of Streptomycetes 



What has been said for the actinomycetes 

 as a whole applies particularly to the large, 

 heterogeneous, and variable group of organ- 

 isms represented in nature by the aerial my- 

 celium-producing strains, most of which are 

 included at present in the genus Streptomy- 

 ces. These organisms are found in the soil in 

 the form of hundreds of thousands of spores 

 and of bits of mycelium per gram. They are 

 also found extensively in manures and in 

 composts, in various fresh-water basins, in 

 dust, and on food. They are almost entirely 

 absent from peat bogs and the sea. 



The actinomycetes belonging to the genus 

 Streptomyces have recently come to occupy 

 an eminent place because many of them are 

 important producers of antibiotics, vitamins, 

 and enzymes. 



With the growing economic significance of 

 members of the genus, the establishment for 

 each species of certain characteristics which 

 would be adequate to enable the investigator 

 to recognize freshly isolated cultures in well 

 defined specific terms becomes of great theo- 

 retical and practical importance. 



Following the first descriptions of Cohn 

 (1875), very few additional species of the 

 aerial mycelium-producing actinomycetes 

 were recognized until 1914. This was true in 

 spite of the rapidly accumulating literature 

 on the occurrence of such actinomycetes in 

 the soil and in the causation of plant diseases. 

 The common designations were limited 

 largely to the names " Actinomyces albus" 



and "Actinomyces chromogenus," depending 

 on the color of the aerial mycelium or the 

 formation of soluble, dark pigments in com- 

 plex organic media. 



Rossi-Doria (1891) was the first to de- 

 scribe an organism, under the name Strepto- 

 thrix alba, which was later designated as the 

 type of the genus Streptomyces proposed by 

 Waksman and Henrici in 1943. The most 

 important characteristics of this species are 

 its white aerial mycelium and the tendency 

 for colonies to form concentric rings of this 

 aerial mycelium. Rossi-Doria noted the abil- 

 ity of his organisms to grow on numerous 

 complex organic substrates. 



Thaxter (1891), who first described an im- 

 portant economic species, the causative 

 agent of potato scab (which he believed to 

 be a fungus, Oospora), was highly critical of 

 the efforts to describe "species" largely on 

 the basis of cultural properties of the organ- 

 isms. In this respect, the actinomycetes do 

 not differ from any of the other groups of 

 bacteria, where cultural properties and bio- 

 chemical reactions have to supplement in- 

 sufficient morphological information. Physi- 

 ological activities and ecological properties, 

 which are the expression of the response of 

 organisms to their environment, are too 

 numerous and often too variable among ac- 

 tinomycetes to justify unlimited confidence. 



Krainsky (1914), Waksman and Curtis 

 (1916), and Waksman (1919) emphasized 

 the use of synthetic substrates, in addition 

 to organic media. Carbon and nitrogen utili- 

 zation tests were employed. Added attention 

 was given to micromorphology. Many new 

 species were described. Jensen (1930a, 1931) 

 and Duche (1934) added various new species, 

 the latter investigator stressing the use of 

 various combinations of carbohydrates and 

 nitrogenous compounds as media ingredients. 



One of the reasons for the limited recog- 

 nition of species among the aerial mycelium- 

 producing actinomycetes prior to 1914 was 

 the fact that protein-rich media were 



