Misrepair mutagenesis in Myxococcus xanthus: induction of rifampicin-resistant mutants by N-methyl-N'-nitro-N-nitrosoguanidine and ultraviolet-irradiation.

In the ultraviolet (UV)-mutable bacterium, Myxococcus xanthus, dose response curves for the induction of rifampicin-resistant (Rifr) mutants were compared with dose response curves for Weigle(W)-reactivation of the UV-irradiated phage Mx4 at a phage survival of 5 X 10(-6). In most strains examined, including a uvr mutant, these curves are largely similar. Unexpectedly the UV-sensitive strain M. xanthus Bt, which is unable to perform W-reactivation, is nevertheless UV-mutable. This result may indicate that the repair pathway involved in phage reactivation is only partly responsible for UV-mutagenesis or alternatively is not able to act on phage DNA in M. xanthus Bt cells. N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) treatment of M. xanthus cells also results in marked W-reactivation of the UV-irradiated phage Mx4 at the same survival of 5 X 10(-6). The MNNG-stimulated phage reactivation is of the same order of magnitude as the UV-stimulated phage reactivation. Also the dose response curves for the induction of Rifr mutants by MNNG and the MNNG-stimulated phage reactivation are quite similar. This coincidence may indicate that misrepair mutagenesis is involved in both UV and MNNG-mutagenesis. It is suggested that M. xanthus is a useful organism with which to study misrepair mutagenesis in bacteria.