DNA-Mediated Prophage Induction in Bacillus subtilis Lysogenic for φ105c4

Prophage was induced when strains of Bacillus subtilis 168 lysogenic for phi105c4 were grown to competence and exposed to specific bacterial DNAs. The time course of phage production was similar to that observed for mitomycin C induction of wild-type prophage. Induction was directly dependent upon DNA concentration up to levels which were saturating for the transformation of bacterial auxotrophic markers. The extent of induction varied with the source of DNA. The burst of phage induced by DNA isolated from a W23 strain of B. subtilis was fivefold less than that induced by DNA from B. subtilis 168 strains, while B. licheniformis DNA was completely inactive. This order of inducing activity was correlated with the ability of the respective DNAs to transform auxotrophic markers carried by one of the phi105c4 lysogens. Differences in inducing activity also were observed for different forms of phi105 DNA. The DNAs isolated from phi105 phage particles and phi105c4 lysogens were inactive, whereas DNA from cells lysogenized by wild-type phi105 induced a burst of phage. When tested for transforming activity, however, both phi105c4 and phi105 lysogen DNAs were equally effective. An induction mechanism which involves recombination at the prophage insertion site is proposed to explain these differences.