Incorporation of extracellular fatty acids by a fatty acid kinase‐dependent pathway in Staphylococcus aureus

Acyl‐CoA and acyl‐acyl carrier protein (ACP) synthetases activate exogenous fatty acids for incorporation into phospholipids in Gram‐negative bacteria. However, Gram‐positive bacteria utilize an acyltransferase pathway for the biogenesis of phosphatidic acid that begins with the acylation of sn‐glycerol‐3‐phosphate by PlsY using an acyl‐phosphate (acyl‐PO₄) intermediate. PlsX generates acyl‐PO₄ from the acyl‐ACP end‐products of fatty acid synthesis. The plsX gene of Staphylococcus aureus was inactivated and the resulting strain was both a fatty acid auxotroph and required de novo fatty acid synthesis for growth. Exogenous fatty acids were only incorporated into the 1‐position and endogenous acyl groups were channeled into the 2‐position of the phospholipids in strain PDJ39 (ΔplsX). Extracellular fatty acids were not elongated. Removal of the exogenous fatty acid supplement led to the rapid accumulation of intracellular acyl‐ACP and the abrupt cessation of fatty acid synthesis. Extracts from the ΔplsX strain exhibited an ATP‐dependent fatty acid kinase activity, and the acyl‐PO₄ was converted to acyl‐ACP when purified PlsX is added. These data reveal the existence of a novel fatty acid kinase pathway for the incorporation of exogenous fatty acids into S. aureus phospholipids.