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Role of the ø11 Phage Genome in Competence of Staphylococcus aureus

Department of Microbiology, The Wallenberg Laboratory, Uppsala University, Uppsala, Sweden

ABSTRACT

Both phage ø11 and 83A, when present as prophage or when used as helper phage, induce competence for transfection and transformation to the same level in Staphylococcus aureus, strain 8325-4. Cells lysogenized with certain temperature-sensitive (ts) mutants of phage ø11 show competence at the nonpermissive temperature (41 C) without production of infectious phages. Phage ø11ts allele 31 can neither as a prophage nor as a helper phage develop competence under nonpermissive conditions. This mutant appears, therefore, to be mutated in the region of the phage genome controlling competence. The competence level for both transfection and transformation is increased by superinfecting strain 8325-4 (ø11) or 8325-4 (83A) at high multiplicities with phage ø11 with some of its mutants or with phage 83A. This superinfection enhancement appears to require protein synthesis but not deoxyribonucleic acid synthesis as judged from studies with inhibitors of macromolecular synthesis. Besides the phage particle, no extracellular or cell-bound factors so far detected can induce competence. The phage-induced product conferring competence is rapidly synthesized by strain 8325-4 (tsø11₃₁) after shift to permissive conditions, but requires deoxyribonucleic acid and protein synthesis to be expressed. Recombination between the sus mutants of phage ø11 of Kretschmer and Egan and tsø11₃₁ indicate that competence is controlled by an early gene in the lytic cycle which may be expressed also in lysogenic cells. The phage product inducing competence appears to have a half-life of 10 to 15 min in the conditional lethal mutant at shift to nonpermissive temperature. Ultraviolet inactivation of phage ø11 infectivity occurs more rapidly than inactivation of competence induction. In fact, the number of transformants is increased at low doses of irradiation. Competence induction is, however, decreased at high does of ultraviolet irradiation.