Mutagenic effect of ultraviolet radiation on the non-acid-fast strain ofMycobacterium phlei

Abstract

The mutability of the PN strain ofMycobacterium phlei was examined after induction of auxotrophic mutants and of STM and VM-resistant mutants, by UV irradiation. A total of 30 auxotrophic mutants were isolated, most of them amino acid-dependent five purine-dependent, and one uracil-dependent. To induce the mutants higher UV doses had to be used so that the survival of cells in the original suspension would not exceed a few per cent. For further genetic work use can be made of 8 auxotrophic mutants (PN try⁻ura⁻, PN arg⁻ura⁻, PN ileu⁻val⁻, PN ileu⁻, PN leu⁻, PN lys⁻, PN lys⁻-VM^r, PN val⁻), these showing a low frequency of spontaneous reversions. No spontaneous auxotrophic mutants have been found. The frequency of STM and VM-resistant mutants is increased upon UV irradiation, a post-irradiation incubation in a liquid medium without the drug being essential for their phenotypic expression. The highest increase of the number of these mutants is attained after 48 h of post-irradiation incubation and it has been found that, within a certain experimental scatter, the same frequency increase is found on using a complete or a minimal liquid medium. The frequency of spontaneous STM-resistant mutants lies within 5.8×10⁻⁶–8.8×10⁻⁶, of those VM-resistant between 3.1×10⁻⁵ and 4.1×10⁻⁵. The highest frequency of induced STM-resistant mutants lies between 3.0×10⁻⁵ and 9.3×10⁻⁵ and of VM-resistant mutants between 1.1×10⁻⁴ and 2.2×10⁻⁴