[W5-6/ODP-082] Pheromone-responsive bacteriolysin Bac41 maintains plasmid propagation in Enterococcus faecalis
In Enterococcus faecalis, pheromon-responsive conjugative plasmids play an important role on horizontal antimicrobial drug resistance genes transfer. Plasmid-encoded bacteriolysin Bac41 is a selective anti-E. faecalis agent that is considered to provide a competitive advantage to E. faecalis cells that carry the Bac41-coding plasmid. Here, we show that the Bac41 gene clusters were conservatively found in the downstream of pheromone-responsive conjugative transfer gene cluster on pheromone-responsive plasmids. We tested the effect of conjugative pheromone peptide on Bac41 expression. Transcription of Bac41 genes was induced by cognate pheromone peptide as like conjugative transfer genes. As Bac41 gene cluster contains self-immunity gene bacI, Bac41 can selectively exclude on E. faecalis cells without Bac41-coding plasmid. Indeed, in in vitro sequential passage experiment using the Bac41-coding multi-antimicrobial resistance plasmid and its isogenic mutant plasmid with Bac41-inactive point mutation, functional Bac41 did not affect initial trans-conjugation efficiency but significantly increased population of cells harboring the Bac41-plasmid over serial passages. The data suggest that the Bac41 system functions as inter-cellular maintenance system of plasmid excluding plasmid-null E. faecalis cells from population after the pheromone responsive trans-conjugation.