Host-cell reactivation and Weigle reactivation of ultraviolet-irradiated Myxococcus xanthus phages

Myxococcus xanthus DZ1, and particularly M. xanthus B, show a phase variation resulting in tan and yellow pigmented colonies. M. xanthus XK is stable and yellow colonies occur only as rare mutants. The various M. xanthus strains exhibit different resistances to short wave UV. With the exception of M. xanthus XK the yellow types are more resistant than the tan types with the greatest difference found in M. xanthus B. This is probably partly responsible for the enrichment of yellow types during UV irradiation of M. xanthus B tan. By ICR mutagenesis a uvr mutant of M. xanthus XK was isolated. Using this mutant it could be demonstrated that all strains, whether yellow or tan pigmented, are able to hose-cell reactive UV irradiated phages Mx1 and Mx4. The repair efficiency for irradiated Mx1 is approximately 70 to 79% at a survival level of 10%. Weigle reactivation of phase Mx4 occurs in M. xanthus XK and DZ1. The effect is most pronounced in M. xanthus XK with a repair efficiency of 44% at 1% survival. The uvr-1 mutant is also able to W-reactivate phage Mx4. Only the yellow phenotype of M. xanthus B is able to W reactivate the irradiated phage Mx4 ts27htf-1hrm-1 with a similar efficiency to M. xanthus XK.M. xanthus B tan is therefore probably blocked in an inducible repair pathway. The phage Mx1 is W-reactivated by none of the M. xanthus strains used. (author)