Characterisation of MalR, a LacI transcriptional regulator of both maltose and maltodextrin metabolism in Enterococcus faecalis

GRAND, MAXIME; MAGNI, CHRISTIAN; BLANCATO, VÍCTOR S.; HARTKE, AXEL; ESPARIZ, MARTIN; SAUVAGEOT, NICOLAS

Chamonix

Conferencia; 5th International Conference on Enterococci. Chamonix; 2018

Maltodextrinsare linear chains of glycosyl residues commonly encountered during Humanalimentation. In a recent study focused on Enterococcusfaecalis, we evidenced that the mdxEFGoperon (ef1345-1343) encoding a maltodextrin ABC transporter was stronglyupregulated during infection in a mouse model. Mouse organ colonization assayssuggested that mdxEFG are indeed important for E. faecalis pathogenesis.E. faecalis uses two distinct ways tometabolize maltose or maltodextrin longer than four glucoses. In both cases,this bacterium uses a pair of divergent operons: one for sugar uptake and thesecond for degradation. Maltose import and degradation are ensured by aPhosphoTransferase System (PTS) (ef0958) and a Phosphorylase (ef0957),respectively. Maltodextrins longer than four glycosyl residues are importedthrough the in vivo induced ABC transporter and then hydrolysed by MmdH(ef1347). Hitherto, transcriptional regulation of expression of these operonsremains unknown.Using RT-qPCR and EMSA experiments we showedthat MalR, a LacI transcriptional regulator encoded by the last gene of themaltose phosphorylase operon, acts as a direct repressor on expression ofmaltose and maltodextrin operons. After focusing on malR expression, 5´RACE-PCRand transcriptional fusion experiments showed that malR is co-transcribed withthe maltose phosphorylase gene but also through a weak constitutive internalpromoter. Analysis of a malR mutant showed that this regulator is essential forCarbon Catabolite Repression (CCR) of both maltose and maltodextrin operons inpresence of glucose. However, this CCR is independent of CcpA. A global modelof this complex regulation will be proposed.