TetR family regulator FarR variation controls antimicrobial fatty acid efflux in Staphylococcus aureus
Abstract
To colonize human skin and survive within abscesses, Staphylococcus aureus has evolved mechanisms to evade host innate defenses. USA300 has become the predominate community-acquired methicillin-resistant S. aureus (CA-MRSA) clone, which can be in part attributed to detoxification of unsaturated free fatty acids (uFFA) found in sebum and the nares. Our lab has previously identified the TetR family regulator FarR responsible for induction of the resistance-nodulation-division (RND) superfamily efflux pump FarE to promote efflux of toxic uFFA. However, RND family efflux pumps remain poorly characterized in Gram-positive species and the mechanism by which FarR regulates FarE has yet to be determined. Here, we demonstrate a predictive binding pocket in the final helix of the C-terminal ligand-binding domain and the potential for acyl-phosphates as an activating ligand of FarR through in silico techniques. Additionally, growth analyses demonstrate the sufficiency of naturally occurring amino acid variations in FarR to promote increased resistance to uFFA. However, these FarR variants did not promote increased resistance to alternative antimicrobials. These data further characterize the importance of RND family pumps in a Gram-positive background, while illuminating one mechanism by which the FarER system aids in antimicrobial fatty acid resistance.