Waksman 



— 128 — 



Actinomycetes 



ing streptomycin. Some produce grisein (358), some produce other 

 antibiotics, and some produce no antibiotics at all. 



Production of mutants of S. griseiis.— When an active streptomycin- 

 producing culture of S. griseiis is plated out and individual colonies are 

 picked and transferred to agar slants, various inactive strains can be ob- 

 tained. One such type was found to differ from the mother culture by 

 being free from aerial mycelium (395). This strain undergoes more 

 rapid lysis, especially when grown in submerged culture. It produces 





Strep to Ur, , Urzi bs y /O -*/A/2L 

 Glucosc. MG/ML 

 Lactic Ac^, MG/ML 



Fig. 28.— Metabolic changes produced in the medium by Stre^ptomyces sp. 

 RivETT and Peterson, 362). 



Cfro 



an acid reaction in the medium, and yields a more viscous broth. It is 

 sensitive to the antibiotic action of streptomycin, whereas the mother 

 culture is highly resistant to the action of this antibiotic. The active 

 culture and the inactive variant are similar in many of their cultural 

 characteristics, such as lack of dark pigmentation on organic media, pro- 

 teolytic action, and hemolytic capacity. By proper cultivation and se- 

 lection, the inactive asporogenous strain can be made to revert to an 

 active sporulating form which will also produce streptomvcin. 



Another type of inactive variant or mutant was found to differ from 

 the mother culture in the production of a pink or vinaceous pigmenta- 

 tion in the vegetative growth (475). Some of the cultures of S. griseus 



