Analysis of sigma(54)-dependent genes in Enterococcus faecalis: a mannose PTS permease (EIIMan) is involved in sensitivity to a bacteriocin, mesentericin Y105

The sigma (54) RNA polymerase subunit has a prominent role in susceptibilit y of Listeria monocytogenes and Enterococcus faecalis to mesentericin Y105, a class Ila bacteriocin. Consequently, sigma (54)-dependent genes as well as specific activators also required for expression of these genes were sou ght. Five putative sigma (54)-associated activators were detected in the ge nome of E. faecalis V583, and all but one could activate the transcription of permease genes belonging to sugar phosphotransferase systems (PTSs). Int erestingly, these activators display a helicase signature not yet reported in this activator family, which could explain the ATP-dependent mechanism o f DNA unwinding preceding the start of transcription. To find which activat or is linked to susceptibility of E, faecalis to mesentericin Y105, their r espective genes were subsequently interrupted. Among them, only mptR gene i nterruption led to a resistance phenotype, Immediately downstream from mptR , a putative sigma (54)-dependent operon was found to encode a mannose PTS permease, namely Ell(t)(man). Moreover. in liquid culture, glucose and mann ose induced the sensitivity of E. faecalis to mesentericin Y105. Since suga rs have previously been reported to induce PTS permease expression, it appe ars that Ell(t)(Man) expression, presumably induced in the presence of gluc ose and mannose, leads to an enhanced sensitivity of E, faecalis to the bac teriocin. Additional information was gained from knockouts within the perme ase operon, Interruption of the distal mptD gene, which encodes the IID sub unit of Ell(t)(Man), strikingly led to resistance to mesentericin Y105. Mor eover, MptD appears to be a peculiar membrane subunit, bearing an additiona l domain compared to most known IID subunits, According to these results, E ll(t)(Man) is clearly involved in susceptibility to mesentericin Y105 and c ould even be its receptor at the L faecalis surface. Finally, it is hypothe sized that MptD could be responsible for the targeting specificity, via an interaction between its additional domain and mesentericin Y105.