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Our understanding of the molecular mechanisms behind bacteria-phage interactions remains limited. Here we report that a small protein, SrpA, controls core cellular processes in response to phage infection and environmental signals in Pseudomonas aeruginosa. We show that SrpA is essential for efficient genome replication of phage K5, and controls transcription by binding to a palindromic sequence upstream of the phage RNA polymerase gene. We identify potential SrpA-binding sites in 66 promoter regions across the P. aeruginosa genome, and experimentally validate direct binding of SrpA to some of these sites. Using transcriptomics and further experiments, we show that SrpA, directly or indirectly, regulates many cellular processes including cell motility, chemotaxis, biofilm formation, pyocyanin synthesis and protein secretion, as well as virulence in a Caenorhabditis elegans model of infection. Further research on SrpA and similar proteins, which are widely present in many other bacteria, is warranted., You et al. show that SrpA, a small protein widely conserved among bacteria, controls core cellular processes in response to phage infection and environmental signals in Pseudomonas aeruginosa, including cell motility, chemotaxis, biofilm formation, and virulence.

Members of the bacterial genus Aeromonas are important aquatic pathogens that cause severe fish diseases. Here, we characterize a novel lytic phage, Aeromonas virus phiA8-29, isolated from the alimentary tract of a freshwater fish. Transmission electron microscopy showed that phiA8-29 has a long contractile tail and thus can be classified as a member of the family Myoviridae. The phage genome was identified as a double-stranded DNA molecule of 144,974 bp containing 185 open reading frames and nine tRNA-encoding genes. Comparative genomic analysis revealed that the phiA8-29 genome has little similarity to any of the currently sequenced Aeromonas phage genomes. Our data indicate that phiA8-29 is a novel lytic Myoviridae phage that does not belong to any of the known genera.