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Summary: The effects of u.v. irradiation on the survival of Staphylococcus aureus and its phage 𝜙11 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 𝜙11 occurred in wild-type S. aureus and in a uvr mutant but to a lesser extent than has been found for phage λ in E. coli. Reactivation was recA-dependent and was accompanied by u.v.-induced mutagenesis in a temperature-sensitive mutant of 𝜙11. 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.
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