Novel patterns of ultraviolet mutagenesis and Weigle reactivation in Staphylococcus aureus and phage phi 11.

The effects of u.v. irradiation on the survival of Staphylococcus aureus and its phage phi 11 were studied. The recA and uvr mutations affected their survival in a similar way to synonymous mutations in Escherichia coli. Weigle reactivation (W-reactivation) of phi 11 occurred in wild-type S. aureus and in a uvr mutant but to a lesser extent than has been found for phage lambda in E. coli. Reactivation was recA-dependent and was accompanied by u.v.-induced mutagenesis in a temperature-sensitive mutant of phi 11. Bacterial mutation to streptomycin resistance was induced by u.v. and was also recA-dependent. In S. aureus, as in E. coli, u.v. was a more effective mutagen in the uvr genetic background. However, a dose-squared response for u.v.-induced mutation of wild-type and uvr strains of S. aureus to streptomycin resistance, and of a trp auxotroph to tryptophan independence, was found only with u.v. doses below 1 J m-2. We suggest that, in relation to the Uvr mechanism of DNA repair, u.v. mutagenesis in S. aureus involves both repairable and non-repairable lesions. As in E. coli, the uvr genetic background reduced the u.v. dose required for maximal W-reactivation of u.v.-irradiated phage. However, there was no enhancement of W-reactivation by post-irradiation broth incubation of S. aureus. Our results are compatible with a non-inducible mechanism for this phenomenon.