A holin remnant protein encoded by STY1365 is involved in envelope stability of Salmonella enterica serovar Typhi

We characterized STY1365, a small ORF of Salmonella enterica serovar Typhi. This 174-bp ORF encodes a putative product of 57 amino acid residues with a premature stop codon. Nevertheless, bioinformatic analyses revealed that the predicted product of STY1365 has similarity to putative holin genes of Escherichia coli and bacteriophage ΦP27. STY1365 showed a high-level expression at the early log phase and a small corresponding protein product was detected mainly in the inner membrane fraction. Cloning of STY1365 in pSU19 mid-copy-vector produced retardation in S. Typhi growth, increased cell permeability to crystal violet and altered the inner membrane protein profile. Similar results were obtained when STY1365 was induced with isopropyl-β-d-thio-galactoside in pCC1^™ single-copy vector. Our results support the fact that S. Typhi STY1365 encodes a holin remnant protein that is involved in the stability of the bacterial envelope.