Waksman — 124 — Actinomycetes 



and found to be very similar to the 1915 culture. One of these strains 

 (No. D-1) was isolated from an agar plate streaked with the swabbing 

 of a chicken's throat and the other (No. 18-16) from a heavily manured 

 field soil. The two strains were identical in their morphological and 

 cultural characteristics. They were isolated within two or three days 

 of each other. Although it was believed at first that the second culture 

 could not have arisen from the first, the possibility was not entirely 

 eliminated. Both strains were very potent producers of streptomycin, 

 but they differed in the relative amount of the antibiotic produced un- 



Table 



28 : Antibiotic spectra of streptomycin and grisein (357) : — 

 Units per gram of crude preparations* 



Streptomycin X 1,000 Grisein X 1,000 



10 to 30 



10 to 20 



<.l 



<.l 



30 to 100 



0.5 



200 to 300 



25 



10 



<.l 



3 



<.l 



<.l 



10 



<.l 



<.l 



30 



5 



<.l 



der different conditions of culture. No. DT was at first the more active 

 strain, but later it declined in activity, whereas No. 18-16 continued 

 to retain its high potency. The latter became the progenitor of all the 

 cultures that are being used at the present time for the industrial pro- 

 duction of streptomycin. 



When the 1915 isolates of A. griseus were later tested for their 

 ability to produce streptomycin and for their sensitivity to the actino- 

 phage of S. griseus (355), the former were found to produce no strep- 

 tomycin and to be resistant to the phage. 



Upon the irradiation of this culture, Kellner (p. 73) succeeded 

 in obtaining a mutant which had the capacity of forming typical strep- 

 tomycin. This mutant was also sensitive to the phage which is active 



