Genes affecting progression of bacteriophage P22 infection in Salmonella identified by transposon and single gene deletion screens

Bacteriophages rely on their hosts for replication, and many host genes critically determine either viral progeny production or host success via phage resistance. A random insertion transposon library of 240,000 mutants in Salmonella enterica serovar Typhimurium was used to monitor effects of individual bacterial gene disruptions on bacteriophage P22 lytic infection. These experiments revealed candidate host genes that alter the timing of phage P22 propagation. Using a False Discovery Rate of < 0.1, mutations in 235 host genes either blocked or delayed progression of P22 lytic infection, including many genes for which this role was previously unknown. Mutations in 77 genes reduced the survival time of host DNA after infection, including mutations in genes for enterobacterial common antigen (ECA) synthesis and osmoregulated periplasmic glucan (OPG). We also screened over 2000 Salmonella single gene deletion mutants to identify genes that impacted either plaque formation or culture growth rates. The gene encoding the periplasmic membrane protein YajC was newly found to be essential for P22 infection. Targeted mutagenesis of yajC shows that an essentially full-length protein is required for function, and potassium efflux measurements demonstrated that YajC is critical for phage DNA ejection across the cytoplasmic membrane.