AN IMPROVED METHOD FOR ISOLATING BIOCHEMICAL MUTANTS OF STREPTOMYCES GRISEOFLAVUS

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Auxotrophic mutants of Streptomyces griseoflavus have been isolated by the following method. After irradiating conidiospores with ultraviolet light, the survivors, equivalent to 0.1 to 1% of the conidia irradiated, were incubated on complete agar for a week and, to the newly arrived conidia, filtration technique was applied in order to concentrate the growth factor-requiring mutants. They were then recovered among the colonies on a complete medium with the aid of the replica plating method. Preincubation prior to filtration proved important, because the frequency of mutants recovered among colonies on the complete medium was raised from 0.1 to 1% by this process. The mutants required the following growth factors: methionine, arginine, cystine, tryptophan, nicotinic acid, glycine or serine, adenine, xanthine, hypoxanthine or uric acid, and glutamic acid or aspartic acid.