A dedicated three component regulatory system (GSP/Ghk/Grr) activates gallocin transcription in Streptococcus gallolyticus UCN34

Bacteriocins are natural antimicrobial peptides produced by a bacterium to kill closely related competitors. Streptococcus gallolyticus subsp. gallolyticus (Sgg) UCN34 produces a two-component bacteriocin named gallocin to colonize the gut by killing resident enterococci. In the present work, we investigated how gallocin was regulated by deleting individually three genes present in the locus and encoding potentially an inducing peptide (gsp), a histidine kinase (ghk) and a LytTR-containing response regulator (grr). Comparative transcriptional analyses of these three mutants as compared to the WT UCN34 showed that this 3- component regulatory system induces the transcription of the whole gallocin locus encoding gallocin but also five others putative bacteriocins and genes necessary for bacteriocins biosynthesis and secretion. Beside gallocin locus, only two other pairs of genes were coordinately induced in Sgg genome, encoding an ABC transporter and hypothetical proteins. We conclude that this regulatory system appears highly specialized in bacteriocins induction in Sgg UCN34. Whole transcriptomic analysis of Streptococcus gallolyticus subspecies gallolyticus (Sgg) UCN34 WT, Δgsp, Δghk and Δgrr