Extended host range of a β-related corynebacteriophage

Unlike most β-related phages isolated from Corynebacterium diphtheriae, phage 782 readily plaqued on strains of C. ulcerans and C. pseudotuberculosis. The extended host range of phage 782 was not, however, due to a greater ability of the phage to adsorb to bacterial surfaces. Using chemical mutagenesis, a number of phage mutants were isolated which had diminished capacities to infect C. ulcerans, suggesting the existence of a locus ( ehr) for extended host range. Pre-lysogenization of C. ulcerans strains with phage 782, but not its mutant form or other β-related phages, rendered them susceptible to infection by previously excluded phages. An examination of recombinants between phages 782, 17, and β localized ehr to a 7 kilobase region of DNA including attP. The data are compatible with the notion that ehr encodes an anti-restriction function.