CLASSIFICATION OF THE ACTINOMYCETES 23 



maturity but in mass appear tan to gray when viewed without magnifica- 

 tion. 



Streptomyces griseus Group 



S. griseus was first isolated and described by Krainsky in Russia, in 

 1914. Soon afterward, a similar culture was isolated in the United States 

 and described, in 1916, by Waksman and Curtis. Although they designated 

 their culture as S. griseus Krainsky, there are certain marked differences 

 bet een the two descriptions. Since no type culture was available for 

 comparison, the two isolates may be considered as distinct. 



S. griseus Krainsky produced a light gray to dark gray aerial mycelium; 

 the sporophores were spiral-forming, giving rise to tight spirals; growth on 

 potato was colorless, with a brown soluble pigment. On the other hand, 

 S. griseus Waksman and Curtis produced a water-green to yellowish green 

 aerial mycelium; the sporophores were straight and produced in tuft-like 

 masses; growth on potato was yellowish, wrinkled, without any soluble 

 pigment. Since the streptomycin-producing culture isolated in 1943 is identi- 

 cal with the one described by Waksman and Curtis, it must be considered 

 in the light of that description. The same is true of the grisein, candicidin, 

 and other antibiotic-producing strains of S. griseus. There are certain minor 

 differences, however, in the cultural properties of the various strains. 



The important characteristics of S. griseus are, therefore, formation of 

 straight chains of spherical or oval spores, no spiral formation, rapid 

 liquefaction of gelatin, and coagulation of blood serum. 



Streptomyces griseus represents an extremely variable group of organisms. 

 This is true particularly when the cultures are examined from the point of 

 view of their ability to produce antibiotic substances, as pointed out previ- 

 ously. On this basis, the many cultures isolated and studied in detail can 

 be classified into five distinct groups: 



1. Strains which produce streptomycin. The amount of antibiotic pro- 

 duced varies greatly with the individual strain, under different conditions 

 of culture. These strains are as a rule sensitive to actinophage. 



2. Strains which produce grisein or grisein-like substances. These strains 

 are as a rule resistant to actinophage. 



3. Strains which produce the antifungal agent candicidin and produce no 

 antibacterial substance. 



4. Strains which produce other antibiotics active against gram-positive 

 bacteria only. The exact nature of these antibiotics is still unknown. 



5. Strains which produce no antibiotics at all. 



The streptomycin-producing strains of S. griseus give rise readily to 

 mutants. So far, two mutants have been isolated : (a) a colorless form, pro- 



