[Lethal and mutagenic action of N-nitroso-N-methylbiuret on the producers of levorin, amphotericin and mycoheptin]. / Letal'noe i mutagennoe deistvie N-nitrozo-N-metilbiureta na produtsenty levorina, amfoteritsina i mikogeptina.

The lethal and mutagenic effect of N-nitrozo-N-methylbiuret (NMB) on the organisms producing levorin, amphotericin B and mycoheptin was studied. The mutagen effect depended on the dose, culture and physiological state of the spores. NMB had a low mutagenic effect on the levorin-producing organism characterized by high activity and genetic homogenicity with respect to the colony morphology and antibiotic production. As for the organisms producing amphotericin B and mycoheptin characterized by high genetic heterogenicity, significant variation of all the features studied was observed on their exposure to the mutagen. Inspite of diverse reaction of the organisms producing levorin, amphotericin B and mycoheptin to the effect of NMB mutants with increased antibiotic production were obtained from the three cultures. The lethal and mutagenic effect of NMB on the mycoheptin-producing organism depended on the process of the spore DNA replication. The spores during the DNA replication period were least sensitive to the lethal effect of the mutagen and most mutable with the respect to the colony morphology. For selection of highly active and stable strains exposure to NMB of the spores of the mycoheptin-producing organism during replication of DNA proved to be more effective than that of the spores during the lag-phase.

[Comparative study of the action of streptomycin on the variability of levorin and amphotericin B producers]. / Sravnitel'noe izuchenie deistviia streptomitsina na izmenchivost' produtsentov levorina i amfoteritsina B

The study of the effect of streptomycin on viability of Act. levoris, strain LIA=0868 producing levorin and Act. nodosus, strain LIA-0861 producing amphotericin B showed that streptomycin had a lethal effect which increased with increasing of its concentration from I to 6 gamma/ml. While the lethal effect of streptomycin on the above cultures was comparatively the same, it had a selective effect on the levorin-producing organism and a marked inhibitory effect on the amphotericin B-producing organism. The selective effect of streptomycin was evident from inhibition of some types of the morphological mutants and variants characterized by a high level of levorin production and from selection of streptomycin-resistant variants. The inhibitory effect of streptomycin was evident from a marked increase in the number of the morphologically changed colonies and variants characterized by a low level of the antibiotic production.