[Variability in Act. circulatus var. monomycini induced by N-5-nitroso-N-methylbiuret]

The effect of N-5-nitrozo-N-methylbiuret (NMB) on various features of Act. circulatus var. monomycini, an organism producing monomycin was studied. It was found that the lethal effect of NMB depended on the exposure time, prolongation of which resulted in increased numbers of the plus variants, morphological and auxotrophic mutations and reverses into the populations of the monomycin-producing organism. An increase in the temperature of the treatment had an effect on the frequency of morphological and auxotrophic mutations inducing an increase in the number of the first and some decrease in the number of the second. The fact of specificity in formation of the vitamin B6-deficient auxotrophic mutants of the same type was of special interest. This was probably associated with genetic peculiar properties of the culture. It was supposed that the genes controlling biosynthesis of vitamin B6 were localized on the actinomycete plasmids, elimination of which under the effect of NMB resulted in blocking of vitamin B6 synthesis which in its turn impaired the reactions of transaminations participating in formation of monomycin.