Fine-tuned transcriptional regulation of malate operons in Enterococcus faecalis

MORTERA, P.; ESPARIZ, M.; SUAREZ, C.; REPIZO, G.; DEUTSCHER, J.; ALARCON, S.; BLANCATO, V.; MAGNI, C.

APPLIED AND ENVIRONMENTAL MICROBIOLOGY

AMER SOC MICROBIOLOGY

Lugar: Washington; Año: 2012 vol. 78 p. 1936 - 1945

0099-2240

In E. faecalis, the mae locus is constituted by two putative divergent operons, maePE and maeKR. The first operon encodes a putative H+/malate symporter (maeP) and a malic enzyme (maeE) previously shown to be essential for malate utilization in this bacterium. The maeKR operon encodes two putative proteins with significant similarity to two-component systems involved in sensing malate and activating its assimilation in bacteria. Our trascriptional and genetic assays showed that maePE and maeKR are induced in response to malate by the response regulator maeR. In addition, we observed that both operons were partially repressed in the presence of glucose. Accordingly, co-metabolism of this sugar and malate was detected. Binding of the complex formed by CcpA and its co-repressor P-Ser-HPr to a cre site located in the mae region was demostrated in vitro and explains the carbon catabolite repression (CCR) observed for the maePE operon. However, our results also porvide evidence for a CcpA independent CCR mechanism regulating the expression of both operons. Finally, a biomass increment by 40% or 75% was observed compared to cellgrown only on glucose or malate, respectively. Cell co-metabolizing both carbon sources exhibit a higher rate of glucose consumption and a lower rate of malate utilization. The growth improvement achieved by E. faecalis during glucose-malate co-metabolism might explain why this microorganism employs different regulatory systems to tightly control the assimilation of both carbon sources.