Anaerobic oxidation of n-dodecane by an addition reaction in a sulfate-reducing bacterial enrichment culture

We identified trace metabolites produced during the anaerobic biodegradatio n of H-26- and D-26-n-dodecane by an enrichment culture that mineralizes th ese compounds in a sulfate-dependent fashion, The metabolites are dodecylsu ccinic acids that, in the case of the perdeuterated substrate, retain all o f the deuterium atoms. The deuterium retention and the gas chromatography-m ass spectrometry fragmentation patterns of the derivatized metabolites sugg est that they are formed by C-H or C-D addition across the double bond of f umarate, As trimethylsilyl eaters, two nearly coeluting metabolites of equa l abundance with nearly identical mass spectra were detected from each of H -26- and D-26-dodecane, but as methyl esters, only a single metabolite peak was detected for each parent substrate, An authentic standard of protonate d n-dodecylsuccinic acid that was synthesized and derivatized by the two me thods had the same fragmentation patterns as the metabolites of H-26-dodeca ne. However, the standard gave only a single peak for each ester type and g as chromatographic retention times different from those of the derivatized metabolites, This suggests that the succinyl moiety in the dodecylsuccinic acid metabolites is attached not at the terminal methyl group of the alkane but at a subterminal position. The detection of two equally abundant trime thylsilyl-esterified metabolites in culture extracts suggests that the anal ysis is resolving diastereomers which have the succinyl moiety located at t he same subterminal carbon in two different absolute configurations. Altern atively, there may be more than one methylene group in the alkane that unde rgoes the proposed fumarate addition reaction, giving at least two structur al isomers in equal amounts.