Effects of hydrocarbon structure on fatty acid, fatty alcohol, and β‐hydroxy acid composition in the hydrocarbon‐degrading bacterium Marinobacter hydrocarbonoclasticus

Abstract

The lipids of the gram-negative bacterium Marinobacter hydrocarbonoclasticus grown in a synthetic seawater medium supplemented with various hydrocarbons as the sole carbon source were isolated, purified, and their structures determined. The hydrocarbons were normal, iso, anteiso, and mid-chain branched alkanes, phenylalkanes, cyclohexylalkanes, and a terminal olefin. According to the sequential procedure used for lipid extraction, three pools were isolated: unbound lipids extracted with organic solvents (corresponding to metabolic lipids and to the main part of membrane lipids), OH- labile lipids [mainly ester-bound in the lipopolysaccharides (LPS)], and H+ labile lipids (mainly amide-bound in the LPS). Each pool contained FA, fatty alcohols, and beta-hydroxy acids. The proportions of these lipids in the unbound lipid pools were 84-98%, 1.1-11.6%, and 0.1-3.6% (w/w), respectively. The chemical structures of the lipids were strongly correlated with those of the hydrocarbons fed; analytical data suggested a metabolism essentially through oxidation into primary alcohol, then into FA and degradation via the beta-oxidation pathway. Sub-terminal oxidation of the hydrocarbon chains, alpha-oxidation of FA or double-bond oxidation in the case of the terminal olefin, were minor, although sometimes substantial, routes of hydrocarbon degradation. Cyclohexyldodecane did not support growth, likely because of the toxicity of cyclohexylacetic acid formed in the oxidation of the alkyl side chain. In the OH- and H+ labile lipid pools, beta-hydroxy acids, the lipophilic moiety of LPS, generally dominated (28-72% and 64-98%, w/w, respectively). The most remarkable feature of these cultures on hydrocarbons was the incorporation in LPS of beta-hydroxy acids with Codd, omega-unsaturated, iso, or anteiso alkyl chains in addition to the specific beta-hydroxy acid of M. hydrocarbonoclasticus, 3-OH-n-12:0. These beta-hydroxy acids were tolerated insofar as their geometry and steric hindrance were close to those of the 3-OH-n-12:0 acid.