[Variability of Act. noursei, the producer of nystatin, under the influence of the separate and combined actions of hydrogen peroxide and UV rays].

The lethal and mutagenic effect of hydrogen dioxide used alone and in combination with UV light on the nystatin-producing strain 408 of Act. noursei was studied. The spore survival decreased with an increase in the hydrogen dioxide concentration and the irradiation dose. When the above mutagens were used in combination the lethality was close to the expected one on the summation effect. Under the effect of hydrogen dioxide and most of its combinations with UV light the morphological variation of strain 408 was close to the natural variation or somewhat lower. This phenomenon was possibly associated with significant lethal effect of hydrogen dioxide on the morphologically changed forms of the strain. Variation of the nystatin-roducing strain with respect to nystatin production increased mainly at the account of higher rate of low active variants especially under combined effect of the mutagens. The lethal and mutagenic effect of the combined use of hydrogen dioxide and UV light on the nystatin-producing organism did not depend on the exposure sequence.