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

GRAND, M; BLANCATO, VS; ESPARIZ, M; MAGNI, C; HARTKE, A; SAUVAGEOT, NICOLAS

Chamonix

Conferencia; 5th International Conference on Enterococci; 2018

ICE

Maltodextrins are linear chains of glycosyl residues commonly encountered during Human alimentation. In a recent study focused on Enterococcus faecalis, we evidenced that the mdxEFG operon (ef1345-1343) encoding a maltodextrin ABC transporter was strongly upregulated during infection in a mouse model. Mouse organ colonization assays suggested that mdxEFG are indeed important for E. faecalis pathogenesis.E. faecalis uses two distinct ways to metabolize maltose or maltodextrin longer than four glucoses. In both cases, this bacterium uses a pair of divergent operons: one for sugar uptake and the second for degradation. Maltose import and degradation are ensured by a PhosphoTransferase System (PTS) (ef0958) and a Phosphorylase (ef0957), respectively. Maltodextrins longer than four glycosyl residues are imported through the in vivo induced ABC transporter and then hydrolysed by MmdH (ef1347). Hitherto, transcriptional regulation of expression of these operons remains unknown.Using RT-qPCR and EMSA experiments we showed that MalR, a LacI transcriptional regulator encoded by the last gene of the maltose phosphorylase operon, acts as a direct repressor on expression of maltose and maltodextrin operons. After focusing on malR expression, 5´RACE-PCR and transcriptional fusion experiments showed that malR is co-transcribed with the maltose phosphorylase gene but also through a weak constitutive internal promoter. Analysis of a malR mutant showed that this regulator is essential for Carbon Catabolite Repression (CCR) of both maltose and maltodextrin operons in presence of glucose. However, this CCR is independent of CcpA. A global model of this complex regulation will be proposed.