Characterization of the Role of the Divalent Metal Ion-Dependent Transcriptional Repressor MntR in the Virulence of Staphylococcus aureus

Abstract

ABSTRACT DtxR-type metal ion-dependent repressors, present in many bacterial pathogens, may regulate expression of virulence genes such as that encoding diphtheria toxin. SirR, a DtxR homologue initially identified in Staphylococcus epidermidis , governs the expression of the adjacent sitABC operon encoding a putative metal ion ABC transporter system. We identified a sirR homologue, mntR , in Staphylococcus aureus and demonstrated by gel shift assay that the corynebacterial repressor DtxR binds to the S. aureus mntABC operator in the presence of Fe 2+ or Mn 2+ . Since a mutant DtxR, DtxR(E175K), functions as an iron-independent hyperrepressor in certain settings, we constructed a heterodiploid S. aureus strain expressing dtxR ( E175K ) from the native mntR promoter. Transcription of the S. aureus mntABC operon was repressed in the presence of Fe 2+ or Mn 2+ in wild-type and heterodiploid S. aureus strains. Under metal ion-limiting conditions, mntABC transcription was reduced but not abolished in S. aureus isolates expressing dtxR ( E175K ) compared with an isogenic control, suggesting that DtxR(E175K) binds the S. aureus MntR box in vivo. Under all conditions tested, mntABC transcription in the dtxR ( E175K )-expressing strain was reduced relative to the isogenic control, indicating that DtxR(E175K) function was constitutively active. In the mouse skin abscess model, dtxR ( E175K )-expressing S. aureus recombinants showed significantly reduced CFU levels compared with the isogenic wild-type control. We conclude that the S. aureus MntR box is recognized by corynebacterial DtxR proteins and thus belongs to the DtxR family of metal-dependent operator sites. Moreover, constitutive repression by DtxR(E175K) reduces the virulence of S. aureus in the mouse skin abscess model.