FORMATION OF N-ALKANE- AND CYCLOALKANE-DERIVED ORGANIC ACIDS DURING ANAEROBIC GROWTH OF A DENITRIFYING BACTERIUM WITH CRUDE OIL

Abstract

The formation of metabolites during anaerobic biodegradation of saturated hydrocarbons directly from crude oil in the absence of oxygen was investigated using a denitrifying bacterium, the Azoarcus-like strain HxN1, which can utilise C6-C8 n-alkanes anaerobically as growth substrates. Various alkylsuccinates (apparently diastereomers) with alkyl chains (probably linked at C-2) ranging from C4 to C8 were detected by gas chromatography-mass spectrometry. These metabolites apparently result from the activation reaction of C4-C8 alkanes with cellular fumarate, analogous to the recently established reaction of pure n-hexane with fumarate in strain HxN1 to yield (1-methylpentyl)succinate. Other succinates carried substituents derived from cyclopentane and methylcyclopentane and hence indicated an activation of such cycloalkanes. Since n-butane, n-pentane or cycloalkanes as single compounds did not support growth of strain HxN1, their apparent products point to co-metabolic reactions during utilisation of the C6-C8 n-alkanes. Furthermore, methyl-branched and cyclopentyl-substituted fatty acids were detected. This finding is explained by a further metabolism of the substituted succinates via carbon skeleton rearrangement and decarboxylation. All metabolites detected in the oil-grown cultures were also identified in cultures grown with defined mixtures of saturated hydrocarbons. Results are of potential value for an understanding of metabolite formation in hydrocarbon-rich anoxic environments from the viewpoint of bacterial physiology.