Manganese-dependent regulation of the endocarditis-associated virulence factor EfaA of Enterococcus faecalis

There is increasing recognition of the emerging role of manganese regulation and acquisition in some pathogenic bacteria. Expression of the Enterococcus faecalis endocarditis-associated virulence factor EfaA is induced by growth in serum. It is demonstrated here that expression of the efaCBA operon encoding a putative ABC-type transporter is regulated by Mn(2+). Transcription of efaCBA and EfaA production were repressed in Mn(2+)-supplemented medium. A Mn(2+)-responsive transcriptional regulator, EfaR, sharing 27 % identity with the Corynebacterium diphtheriae diphtheria toxin repressor (DtxR), was identified. In the presence of Mn(2+), EfaR protein bound in vitro to the efaC promoter region. Analysis of the E. faecalis V583 genome revealed ten additional putative EfaR-binding sites, suggesting that manganese availability could have a broader regulatory role in infection. The results identify a new Mn(2+)-sensing regulator in enterococci that regulates the expression of a virulence factor implicated in enterococcal endocarditis.