Incorporation of 1‐chlorooctadecane into FA and β‐hydroxy acids of Marinobacter hydrocarbonoclasticus

Abstract

The lipids of the gram-negative marine bacterium Marinobacter hydrocarbonoclasticus, cultivated in synthetic seawater supplemented with 1-chlorooctadecane as sole source of carbon, were isolated, purified, and their structures determined. Three pools of lipids were isolated according to the sequential procedure used: unbound lipids extracted by organic solvents, ester-bound lipids released under alkaline conditions, and amide-bound lipids released by acid hydrolysis. FA isolated from the unbound lipids included omega-chlorinated (21%, w/w, of this fraction; C16 predominant) and nonchlorinated compounds (22%, w/w; C18 predominant). These acids were accompanied by a high proportion of omega-chloro-C18 alcohols (43%, w/w) and a lower amount of omega-chloro-beta-hydroxy-C18, -C16, and -C14 acids (5%, w/w). These data, together with the isolation from the culture medium of gamma-butyrolactone, suggested a metabolism of 1-chlorooctadecane through oxidation into omega-chloro acid and then the classic beta-oxidation pathway. The analysis of the ester-bound and amide-bound lipids revealed that significant amounts of omega-chloro-beta-hydroxy C10-C12 acids were incorporated into the lipopolysaccharides of the bacterium. Incorporation of these omega-chloro-beta-hydroxy acids into the lipopolysaccharides represents a novel route for chloroalkane assimilation in hydrocarbonoclastic gram-negative bacteria. The formation of chlorinated hydroxy acids, like the omega-chloro FA in the cellular lipids, could account for an incomplete mineralization of chloroparaffins in the environment.

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

“…They exhibit carbon atom numbers in the range of C 14 -C 20 , resulting from the metabolism of the hydrocarbons, and their chemical structures are closely related to those of the hydrocarbons fed. By contrast, the bound β-hydroxy acids have carbon atom numbers in the range of C 10 -C 14 , with a maximum at n-12:0, as previously observed in cultures on n-eicosane, ammonium acetate, 1-chlorooctadecane, or a complex medium (12,14,15). Comparison of the profiles of the bound β-hydroxy acids shows some differences, however.…”

“…In addition, in a recent work on the degradation of 1-chlorooctadecane by M. hydrocarbonoclasticus, we observed that ca. 10% of the hydroxy acids in LPS were ω-chlorinated (15). Together, these data suggest that LPS can incorporate nonspecific β-hydroxy acids insofar as their steric hindrance and geometry do not markedly differ from those of the specific β-hydroxy acids synthesized by the bacterium in complex media.…”

“…The dry biomass of each culture was submitted to a sequential extraction procedure to extract the totality of lipids (14,15). In brief, the main part of the free and membrane lipids was recovered by extraction with chloroform/methanol.…”

“…Three n-C 19 fatty alcohols were identified in the unbound lipids of the n-C 19 culture ( Table 2): two primary (a saturated and an unsaturated) and a secondary with the hydroxyl group at the subterminal position. The oddness/evenness of the hydrocarbon chain length of β-hydroxy acids depended on the alkane fed, with C 19 and Data taken from a previous study (15). c ND, not determined.…”

“…This ubiquitous bacterium is able to use straight-chain hydrocarbons as the sole carbon source (12)(13)(14). Analytical data have suggested a metabolism of these compounds through oxidation into acids, and then through the classical β-oxidation pathway via β-hydroxy acids (14,15). In M. hydrocarbonoclasticus grown on n-eicosane, long-chain β-hydroxy acids (C 16 -C 20 ) were identified in the lipids extracted with solvents.…”