Hydroxy fatty acids in marine dissolved organic matter as indicators of bacterial membrane material

Samples of ultrafiltered dissolved organic matter (UDOM) from the equatorial Pacific Ocean, Gulf of Mexico, and North Sea were analyzed for lipid biomarkers to evaluate potential inputs from bacterial membrane lipids. Acid hydrolysis released a series of C12–C20 fatty acids and C10–C18 β-hydroxy fatty acids (3-hydroxy acids), with total acid (fatty + hydroxy) concentrations of 0.039–0.31 nM or about 0.006–0.087% of ultrafiltered dissolved organic carbon (UDOC). β-hydroxy acids comprised from 6 to 91% of total (fatty + hydroxy) acids in UDOM. Short-chain β-hydroxy acids of this type are constituents of the structural lipopolysaccharide biopolymers of bacterial membranes, especially in Gram negative species. The data suggest that bacterial membrane-derived lipid material may be a component of marine DOM, and our results point to the need for additional lipid analyses of marine UDOM to better characterize its source(s).