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

Abstract

Oleate hydratases (OhyAs) belong to a large family of bacterial proteins catalyzing the hydration or isomerization of double bonds in unsaturated fatty acids. A <i>Staphylococcus aureus</i> gene (<i>Sa0102</i>) is predicted to encode an OhyA. Here, we recombinantly expressed and purified <i>Sa</i>OhyA and found that it forms a homodimer that requires FAD for activity. <i>Sa</i>OhyA hydrates only unsaturated fatty acids containing <i>cis</i>-9 double bonds, but not fatty acids with <i>trans</i>-9 double bonds or <i>cis</i> double bonds at other positions. <i>Sa</i>OhyA products were not detected in <i>S. aureus</i> phospholipids and were released into the growth medium. <i>S. aureus</i> does not synthesize unsaturated fatty acids, and the <i>Sa</i>OhyA substrates are derived from infection sites. Palmitoleate (16:1(9<i>Z</i>)) is a major mammalian skin-produced antimicrobial fatty acid that protects against <i>S. aureus</i> infection, and we observed that it is an <i>Sa</i>OhyA substrate and that its hydroxylated derivative is not antimicrobial. Treatment of <i>S. aureus</i> with 24 μm 16:1(9<i>Z</i>) immediately arrested growth, followed by growth resumption after a lag period of 2 h. The Δ<i>ohyA</i> mutant strain did not recover from the 16:1(9<i>Z</i>) challenge, and increasing <i>Sa</i>OhyA expression using a plasmid system prevented the initial growth arrest. Challenging <i>S. aureus</i> with sapienic acid (16:1(6<i>Z</i>)), an antimicrobial fatty acid produced only by human skin, arrested growth without recovery in WT, Δ<i>ohyA</i>, and <i>Sa</i>OhyA-overexpressing strains. We conclude that <i>Sa</i>OhyA protects <i>S. aureus</i> 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.