DNA-Mediated Prophage Induction in Bacillus subtilis Lysogenic for φ105c4

Abstract

Prophage was induced when strains of Bacillus subtilis 168 lysogenic for φ105c4 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 φ105c4 lysogens. Differences in inducing activity also were observed for different forms of φ105 DNA. The DNAs isolated from φ105 phage particles and φ105c4 lysogens were inactive, whereas DNA from cells lysogenized by wild-type φ105 induced a burst of phage. When tested for transforming activity, however, both φ105c4 and φ105 lysogen DNAs were equally effective. An induction mechanism which involves recombination at the prophage insertion site is proposed to explain these differences.