The study of variability and strain selection in Streptomyces atroolivaceus. I. UV light and nitrous acid as effective agents in the improvement of mithramycin production

Strain improvement in Streptomyces galilaeus, a producer of anthracycline antibiotics galirubins

The production of epsilon-pyrromycinone glycosides in Streptomyces galilaeus increased 12-fold, with respect to the wild strain, as a result of a sequential procedure including both natural selection and treatment with mutagens (nitrous acid, UV light and gamma-irradiation). Nitrous acid exhibited the highest mutagenic effect, both in increasing the productivity and in inducing blocked mutants. A mutant strain blocked in the biosynthesis of glycosides and accumulating free epsilon-pyrromycinone as the principal metabolite was obtained.

Spontaneous and induced variability in Streptomyces nogalater producing nogalamycin

Variability in the production of nogalamycin by Streptomyces nogalater var. nogalater was followed in untreated and mutagenized populations of the standard strain NRRL 3035 and its spontaneous variant K-18 using the method of agar blocks with subsequent tests under submerged conditions. In both strains the most active variants were obtained by natural selection without mutagenic treatment; in this way productivity increased by 108% after two selection steps. Treatment with UV-radiation did not yield variants with a highly increased activity. Gamma-radiation extended the variability but, at the same, substantially increased the number of non-producing and low-producing isolates. Relatively high yields of (+)-variants were obtained after treatment with nitrous acid but their activity did not reach that observed in the most active spontaneous variants.

The study of variability and strain selection in Streptomyces atroolivaceus. III. Isolation and preliminary characteristics of mutants impaired in the biosynthesis of mithramycin

Mutants of Streptomyces atroolivaceus blocked in the biosynthesis of mithramycin were isolated both by natural selection and after treatment with mutagenic factors (UV and gamma rays, nitrous acid). Both physical factors were more effective than nitrous acid. The selection was complicated by a high instability of isolates, out of which 20-80% (depending on their origin) reversed spontaneously to the parent type. The primary screening (selection of morphological variants and determination of their activity using the method of agar blocks) made it possible to detect only potentially non-productive strains; however, the final selection had to be performed always under submerged conditions. Fifty-four stable non-productive mutants were divided, according to results of the chromatographic analysis, in five groups differing in production of six biologically inactive metabolites (compounds A-H). The mutants did not accumulate chromomycinone, chromocyclomycin and chromocyclin. On mixed cultivation none of the pairs of mutants was capable of cosynthesis of mithramycin or new compounds differing from standard metabolites. Possible causes of the above results are discussed.