Characterization of the Ers regulon of Enterococcus faecalis

Ers has been qualified as the PrfA-like transcriptional regulator of Enterococcus faecalis. In a previous study we reported that Ers is important for the survival within macrophages of this opportunist pathogenic bacterium. In the present work we have used proteomic and microarray expression profiling of E. faecalis JH2-2 and an ers-deleted mutant (Delta ers mutant) strains to define the Ers regulon. In addition to EF_0082 (encoding a putative facilitator family transporter), already known to be under Ers regulation, three genes or operons displayed a significant decrease (confirmed by reverse transcription quantitative PCR) in expression in the Delta ers mutant. The first locus corresponds to three genes: arcA, arcB, and arcC1 (arcABC). These genes are members of the ADI operon, encoding enzymes of the arginine deiminase system. The second is the EF_1459 gene, which encodes a hypothetical protein and is located within a putative phage genetic element. Lastly, Ef_3319 is annotated as the alpha subunit of the citrate lyase encoded by citF. citF is a member of a putative 12-gene operon involved in citrate catabolism. Moreover, the promoter sequence, similar to the "PrfA box" and found in the promoter regions of ers and EF_0082, has been shown to be included in the DNA segment recognized by Ers. Phenotypic analysis of the Delta ers mutant strain revealed a growth defect when cultured with arginine or citrate as the energy source; this was not seen for the wild type. As expected, similar results were obtained with mutants in which arcA and citF were inactivated. In addition, in the mouse peritonitis model of virulence, the Delta ers mutant appeared significantly less lethal than the JH2-2 wild-type strain. Taken together, these results indicate that the regulator Ers has a pleiotropic effect, especially in the cellular metabolism and virulence of E. faecalis.