Genetic studies of hybrids between coliphage lambda and salmonella phage P22: genetic analysis of the P22-lambda hybrid class

Activation of a prophage-encoded tyrosine kinase by a heterologous infecting phage results in a self-inflicted abortive infection

Bacteria in their struggle for survival have evolved or acquired defences against attacking phage. However, phage often contribute to this defence through mechanisms in which a prophage protects the bacterial population from attack by another, often unrelated, phage. The 933W prophage, which carries Shiga toxin genes that enhance pathogenicity of enterohaemorrhagic Escherichia coli strain O157:H7, also carries the stk gene encoding a eukaryotic-like tyrosine kinase that excludes (aborts) infection by phage HK97. This exclusion requires the kinase activity of Stk. Little, if any, protein tyrosine phosphorylation can be detected in a 933W lysogen prior to infection with HK97, while extensive Stk-mediated tyrosine phosphorylation is evident following infection. This includes autophosphorylation that stabilizes Stk protein from degradation. Although increased levels of Stk are found following HK97 infection, these higher levels are not necessary or sufficient for exclusion or protein phosphorylation. An HK97 open reading frame, orf41, is necessary for exclusion and Stk kinase activity. We hypothesize that interaction with gp41 stimulates Stk kinase activity. Exclusion of HK97 appears to be specific since other phages tested, λ, φ80, H-19B, λ-P22dis and T4rII, were not excluded. Infection of the 933W lysogen with a non-excluded phage fails to induce Stk-determined phosphorylation.

Genomic structure of phage F22, a hybrid between serologically and morphologically unrelated Salmonella typhimurium bacteriophages P22 and Fels 2

Salmonella typhimuriumphage P22 can recombine with a serologically and morphologically unrelated Salmonella phageFels 2to yield the hybrid phage F22 at a frequency of about 10−12. F22 has inherited the entire late genes (protein coat and tail structural genes) ofFels 2but carries some P22 early genes. P22 genes in the F22 phage were indentified by marker rescue of various P22 mutants. The F22 genome carries thex-erf-c-18-12segment of the P22 genome. A number of P22 amber mutants were also tested to support these data. The F22 region homologous to P22 was mapped by scoring the ratio of P22 backcross recombinant types in lysates of F22 lysogens superinfected with P22c2ts12. The ratio of the distances between these markers and the ends of the homologous region was determined. Furthermore a new F22 hybrid designated F22dis, containing both P22 immunity regions (candIm), was isolated at a frequency of about 10−4by superinfecting F22 lysogens with P22. F22disphage has lost someFels 2gene(s) which have been replaced by the P22 segment containing theImregion, resulting in formation of a defective hybrid phage.

Anaerobic cultures of Salmonella typhimurium do not exhibit inducible proteolytic function of the recA gene and recBC function

In a strict anaerobic environment, lack of expression of bacterial recBC function and recA regulatory functions for the SOS repair system is demonstrated by the use of the carcinogenesis-mutagenesis assay and Salmonella phage P22 mutants requiring these host functions for replication. Therefore, we suggest that error-prone repair (SOS repair) is confined to aerobic environments in facultative anaerobes.