Regulation of the maeEP operon encoding the malate utilization pathway in Enterococus Faecalis.

MORTERA, P.; ESPARIZ, M.; REPIZO, G.; BLANCATO, V.; ALARCON, S. H.; MAGNI, C.

Tucuman, Argentina

Simposio; III Simposio Internacional de Bacterias Lácticas y Segundo Encuentro Red Bal Argentina.; 2009

CERELA (Centro de Referencia para Lactobacilos)

Malic enzymes are disseminated from eukaryotes to prokaryotes. In Lactic Acid Bacteria (LAB) three different types of malic enzymes were described. Only two genes coding for this family of proteins were identified in Enterococcus faecalis chromosome. citM gene encoding an oxaloacetate decarboxylase associated to the citrate metabolism and maeE (EF1207), which is linked to maeP (EF1206, encoding a malate transporter). maePE operon was identified on the E. faecalis V583 chromosome nearby to the maeS (EF1209) and maeR (EF1210) genes, which encode the two-component system involved in the positive activation of this operon. MaeS and MaeR present homology to citrate/malate sensor kinases and response regulators, respectively, found in several microorganisms. In this communication we analysed the regulation of the malate utilization in E. faecalis and present evidence for the role of the mae locus. Inactivation of the maePE operon or the sensor-regulator pair maeSR caused complete loss of malate utilization in E. faecalis. Malate utilization was analysed in E. faecalis by measuring the cytoplasmic alkalinization of the cells, which is associated to its consumption. In order to achieve that, we evaluated resting cells internal pH changes in enterococcal cells grown in different media by using the fluorescent probe BCECF. No signal was found in the absence of malate or when glucose (or other PTS sugars) were added to the growth medium. Moreover, by a bioinformatic approach we identified multiple cre sites (catabolite- responsive element) in the intergenic region between the maePE and maeRS operons and in the coding region of maeP and maeR. This strongly support the PTS sugar hierarchical preference over malate above described. Finally, the effect of pH in malate growing E. faecalis cells was evaluated. Surprisingly, for acid pre-adapted bacteria the metabolism of malate was only observed when the initial external pH of the growth medium was set above 4.5 units.