title: Fine-tuned transcriptional regulation of malate operons in Enterococcus faecalis.
abstract: In Enterococcus 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 transcriptional 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, the cometabolism of this sugar and malate was detected. The binding of the complex formed by CcpA and its corepressor P-Ser-HPr to a cre site located in the mae region was demonstrated in vitro and explains the carbon catabolite repression (CCR) observed for the maePE operon. However, our results also provide evidence for a CcpA-independent CCR mechanism regulating the expression of both operons. Finally, a biomass increment of 40 or 75% was observed compared to the biomass of cells grown only on glucose or malate, respectively. Cells cometabolizing 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 cometabolism might explain why this microorganism employs different regulatory systems to tightly control the assimilation of both carbon sources.
authors.affiliation: Instituto de Biología Molecular y Celular de Rosario (IBR-CONICET) and Departamento de Microbiología, Facultad de Ciencias Bioquímicas y Farmacéuticas (FCByF), Universidad Nacional de Rosario (UNR), Suipacha, Rosario, Argentina.
authors.forename: Pablo
authors.initials: P
authors.lastname: Mortera
authors.forename: Martín
authors.initials: M
authors.lastname: Espariz
authors.forename: Cristian
authors.initials: C
authors.lastname: Suárez
authors.forename: Guillermo
authors.initials: G
authors.lastname: Repizo
authors.forename: Josef
authors.initials: J
authors.lastname: Deutscher
authors.forename: Sergio
authors.initials: S
authors.lastname: Alarcón
authors.forename: Víctor
authors.initials: V
authors.lastname: Blancato
authors.forename: Christian
authors.initials: C
authors.lastname: Magni
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D018533:Biomass; D013293:Enterococcus faecalis / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D005947:Glucose / Q000378:metabolism; D008293:Malates / Q000378:metabolism*; D009876:Operon; D014158:Transcription, Genetic
chemical_list: D001426:Bacterial Proteins; D008293:Malates; C030298:malic acid; D005947:Glucose