Genetic studies of hybrids between coliphage phi 80 and Salmonella phage P22

Hybrids between Escherichia coli phage phi 80 and Salmonella typhimurium phage P22 were isolated after superinfection by P22 of a smooth E. coli-S. typhimurium hybrid lysogenic for phi 80. These hybrid phages, designated phi 80immP22 and phi 80immP22dis, possessed the phi 80 protein coat and tail genes. The phi 80immP22 hybrids acquired the immunity (immC) region of P22 and some adjacent P22 genes, but E. coli-S. typhimurium strains lysogenic for phi 80immP22 hybrids remained sensitive to P22. The phi 80immP22dis hybrids, found ten times more frequently than the phi 80immP22 hybrids, contained a more extensive portion of the P22 genome which encompassed the immI as well as the immC region of P22. Therefore, the phi 80immP22dis hybrids conferred on their hosts immunity to P22 infection. Further analyses have revealed that the phi 80immP22dis hybrids carry the P22 attachment region and either P22 tail gene 9 or antigen conversion gene a1, but not both of these genes.