Mating in Bacillus thuringiensis can induce plasmid integrative prophage J7W-1

Bacillus thuringiensis serovar israelensis, a bacterium which possesses pla smid transfer ability after mating, has been lysogenized by plasmid integra tive phage J7W-1. The induction of phage in this J7W-1 lysogen was observed after mating with phage-insensitive strains, such as B. thuringiensis sero var thuringiensis, B. cereus and B. subtilis, as well as the phage-sensitiv e strain serovar israelensis. The phage induction was not observed after ma ting with B. thuringiensis strains AF101, serovar dendrolimus and serovar i ndiana. Because these strains are naturally associated with J7W-1 or its re lated phage, the data strongly suggest a constitutive expression of the rep ressor encoded by the prophage in these strains. However, the phage inducti on was observed in B. thuringiensis serovar aizawai, although it contained the J7W-1 DNA homologous region(s).