Restriction and modification in Bacillus subtilis 168. Regulation of hsrM(nonB) expression in spoOA mutants and effects on permissiveness for phi15 and phi105 phages.

Gene hsrM (nonB) of Bacillus subtilis 168, causing non-permissiveness to phage SP10 (Saito et al. 1979) and reduced plating efficiency of unmodified phage ϕ105, is responsible for non-permissiveness of B. subtilis 168 for phages π15 and PZA. Upon transformation to sporulation deficiency (allele spoOA) B. subtilis 168 becomes permissive for ϕ15 and PZA and loses the ability to restrict ϕ105. spoOA str-1 double transformants of B. subtilis 168, however, retain the restriction 168 and non-permissiveness for ϕ15 and PZA phages, in spite of their Spo− phenotype. Therefore it appears that a functional product of the spoOA gene is required for expression of gene hsrM in wild-type bacteria, but is not essential in streptomycin-resistant bacteria. Phage genomes (PZA) were trapped in spores of the restriction deficient strain with much higher efficiency than in the wild-type.