[Growth of Escherichia coli cell culture and frequency of mutation, induced by N-methyl-N'-nitro-N-nitrosoguanidine].

The rate of Escherichia coli mutation with N-methyl-N'-nitro-N-nitrosoguanidine was found to depend on the age of the culture and the pH value of the incubation medium. The mutability of late-logarithmic cells was higher than that of mid-logarithmic cells. Rifampicin, a transcription inhibitor, enhanced the mutagenic action of MNNG on cells from the late logarithmic and early stationary phases suspended in a medium with a pH of 7.4, and on cells from the mid-logarithmic phase suspended in a medium with a pH of 6.5. Conversely, streptomycin decreased the frequency of induced mutations in cells from the late logarithmic and early stationary phases suspended in the medium with a pH of 7.4, and in cells from the mid-logarithmic and early stationary phases suspended in the medium with a pH of 6.5. These data were interpreted as showing that the repair of premutational DNA lesions induced by MNNG depends on the level of DNA transcription and translation.