SER] 



AND SPECIES OF GENUS STREPTOMYCES 



L37 



streptomycin was finally selected and grown 

 in a liquid medium, the streptomycin-like 

 nature of the antibiotic could be established 

 by adding the culture filtrate to a nutrient 

 broth and inoculating the latter with a strep- 

 tomycin-dependenl strain of Escherichia coli 

 or of some other bacterium. Growth of the 

 bacterium definitely established the fact that 

 the unknown antibiotic was streptomycin. 



5. Cross-streaking the unknown cultures 

 on a suitable agar medium toward known 

 streptomycin-producing cultures. The latter 

 exerted only a slight inhibiting effect upon 

 the unknown streptomycin-producers. 



Usually some soil or other material is 

 plated on ordinary agar media favorable to 

 the development of actinomycetes; colonies 

 were picked and tested. The S. griseus col- 

 onies could easily he recognized by the pale 

 green to grayish-green shade of their aerial 

 mycelium. A suitable agar medium can also 

 he seeded with living cells of a nonpatho- 

 genic strain of Mycobacterium tuberculosis 

 and various dilutions of soil used for plating 

 purposes, due plates are first incubated at 

 28-30°C for 2 or :; days, to enable the acti- 

 nomycetes to develop. This is followed by 

 further incubation of the plates at 37°C for 

 the development of the test bacterium. Col- 

 onies thai have the capacity of inhibiting 

 growth of the bacterium are found to be 

 surrounded by clear zones. 



The antibiotic potency of an active culture 

 of S. griseus was found to be fairly constant, 

 in spite of the ability of the culture to give 

 rise to inactive variants. Highly active 

 strains tend to retain their relatively superior 

 streptomycin-producing potency, whereas 

 poor strains usually remain weak producers 

 of this antibiotic. For the commercial pro- 

 duction of streptomycin, however, it is es- 

 sential to select continuously the mosl ac- 

 tive strains. 



Since the streptomycin-producing culture 

 isolated in L943 was found to be identical 

 with the one described by Waksman and 



Curtis, it must be considered in the light of 

 that description. The same is tine of die S. 

 griseus strains isolated later and found to 

 be able to produce grisein, candicidin, vio- 

 niycin, and actinomycin. There are certain 

 differences in the cultural and biochemical 

 properties of the various strains belonging 

 to the Grisi us series, especially in theirability 

 to produce various antibiotic- and in their 

 sensitivity to different phage-. This justifies 

 the separation of the group into several dis- 

 tinct species. 



The morphological and cultural properties 

 of certain cultures belonging to the Griseus 

 series are given in Table 19. 



Characterization 



The Griseus series is characterized by cer- 

 tain morphological and cultural properties 

 that make possible its identification and 

 ready distinction from other groups belong- 

 ing to the genus Streptomyces. As more and 

 more cultures of S. griseus were isolated, it 

 became recognized that this is a large series 

 of organisms, the members of which vary 

 greatly in their physiological properties and 

 in their ability to produce various antibiot- 

 ics. 



Waksman and Curtis described S. griseus 

 as producing on sucrose nitrate agar a thin. 

 spreading growth, developing dee]) into the 

 medium, at first colorless, then turning olive- 

 buff. This color may be lost on successive 

 transfers. The aerial mycelium is thick, pow- 

 dery, water-green in color. No soluble pig- 

 ment was observed; the reverse of the gro\* th 

 became brownish in 24 days. ( )n gelatin. 

 at 18°C, »S'. griseus produced a greenish-yel- 

 low or cream-colored growth developing deep 

 into the substrate; the aerial mycelium was 

 white-gray with a greenish tinge. There was 

 no soluble pigment; liquefaction of the gela- 

 tin was rapid. The culture was capable of 

 utilizing a variety of carbohydrates, includ- 

 ing pentoses, hexoses, sugar alcohol-, and 

 organic acids. It was also able to obtain its 



