Overproduction and regulation of repressor of phage P22 in polymyxin B-sensitive mutants of Salmonella typhimurium

Two polymyxin B-sensitive (POX) mutants of Salmonella typhimurium were isolated. One of these mutants, POX-1, proved abnormal in supporting replication of the wild-type phage P22. Compared to the parental host strain, wild-type -4 virus has a very low efficiency of plating (10-4) on the POX-1 mutant, while the C1 and C2 mutants plate with the same efficiency on both host strains. The growth of wild-type phage P22 occurred in the lysogen POX-1 (P22 C+) after UV induction and in C+ infected, POX-1 cells preirradiated with UV light. These results indicate that the POX-1 host is not functionally defective at any stage leading to the normal development of phage P22. The hypothesis favored for the inability of the wild-type virus to multiply in the POX-1 host is the overproduction of repressor by the wild type P22. [...]