Oleate hydratase from protects against palmitoleic acid, the major antimicrobial fatty acid produced by mammalian skin.

Oleate hydratases (OhyAs) belong to a large family of bacterial proteins catalyzing the hydration or isomerization of double bonds in unsaturated fatty acids. A gene () is predicted to encode an OhyA. Here, we recombinantly expressed and purified OhyA and found that it forms a homodimer that requires FAD for activity. OhyA hydrates only unsaturated fatty acids containing -9 double bonds, but not fatty acids with -9 double bonds or double bonds at other positions. OhyA products were not detected in phospholipids and were released into the growth medium. does not synthesize unsaturated fatty acids, and the OhyA substrates are derived from infection sites. Palmitoleate (16:1(9)) is a major mammalian skin-produced antimicrobial fatty acid that protects against infection, and we observed that it is an OhyA substrate and that its hydroxylated derivative is not antimicrobial. Treatment of with 24 μm 16:1(9) immediately arrested growth, followed by growth resumption after a lag period of 2 h. The Δ mutant strain did not recover from the 16:1(9) challenge, and increasing OhyA expression using a plasmid system prevented the initial growth arrest. Challenging with sapienic acid (16:1(6)), an antimicrobial fatty acid produced only by human skin, arrested growth without recovery in WT, Δ, and OhyA-overexpressing strains. We conclude that OhyA protects from palmitoleic acid, the antimicrobial unsaturated fatty acid produced by most mammals, and that sapienic acid, uniquely produced by humans, counters the OhyA-dependent bacterial defense mechanism.