Isolation of streptomycinproducing strains of Streptomyces griseus

In the study of the production of antibiotics by microorganisms, especially when a given substance receives recognition as a chemotherapeutic agent, it becomes necessary, in order to maintain the potency of the culture cr to obtain more active cultures, to isolate fresh strains of the organism producing the particular antibiotic. This can usually be accomplished by two procedures: (1) Fresh cultures of the organism are isolated indiscriminately from various natural substrates, such as soils and composts, and tested for their potency. (2) New strains are obtained by plating the original culture and then isolating individual colonies. Before plating, the culture may be pretreated, as by exposure to different radiations, in order to kill a large number of sensitive spores. Both of these methods have been utilized wwith considerable success in the isolation of more potent strains of penicillin-producing fungi. Compara-tively little progress has been mnade, however, in the case of streptomycin-producing strains of Streptomyces grisnus. It has been established that penicillin production is characteristic of th