Viral mutation affecting bacteriophage phi 1 development in Bacillus subtilis 168.

Bacillus subtilis bacteriophage phi 1m, a host-range variant, was isolated after mutagenesis of virulent bacteriophage phi 1. Unlike its wild-type antecedent, phi 1m could not form plaques on lawns of B subtilis 168 at 37 C, although it adsorbed to, penetrated, and killed this bacterium. Experiments conducted in liquid medium at 37 C showed that B. subtilis 168 cells allowed reduced levels of phi 1m development at low multiplicities of infection, whereas high multiplicity infections of this strain by the phage were abortive. Certain mutants, derived originally from B. subtilis 168, were observed to be permissive for phi 1m at 37 C; moreover, their permissive phenotype could be duplicated by growing wild-type B. subtilis 168 cells at temperatures above 47 C. Studies on phi 1m and host nucleic acid synthesis under nonpermissive conditions demonstrated that transciption and DNA synthesis proceeded up to 20 min after infection, after which time there was a cessation of all nucleic acid production. These observations are discussed with respect to other abortive bacteriophage infections in B. subtilis.