The fadXDEBA locus of Staphylococcus aureus is required for metabolism of exogenous palmitic acid and in vivo growth

In Staphylococcus aureus, genes that should confer the capacity to metabolize fatty acids by beta-oxidation occur in the fadXDEBA locus, but their function has not been elucidated. Previously, incorporation into phospholipid through the fatty acid kinase FakA pathway was thought to be the only option available for S. aureus to metabolize exogenous saturated fatty acids. We now find that in S. aureus USA300, a fadX::lux reporter was repressed by glucose and induced by palmitic acid but not stearic acid, while in USA300 Delta fakA basal expression was significantly elevated, and enhanced in response to both fatty acids. When cultures were supplemented with palmitic acid, palmitoyl-CoA representing the first metabolite in the beta-oxidation pathway was detected in USA300, but not in a fadXDEBA deletion mutant USA300 Delta fad, which relative to USA300 exhibited increased incorporation of palmitic acid into phospholipid accompanied by a rapid loss of viability. USA300 Delta fad also exhibited significantly reduced viability in a murine tissue abscess infection model. Our data are consistent with FakA-mediated incorporation of fatty acids into phospholipid as a preferred pathway for metabolism of exogenous fatty acids, while the fad locus is critical for metabolism of palmitic acid, which is the most abundant free fatty acid in human plasma.