Anaerobic biodegradation of n-hexadecane by a nitrate-reducing consortium.

Nitrate-reducing enrichments, amended with n-hexadecane, were established with petroleum-contaminated sediment from Onondaga Lake. Cultures were serially diluted to yield a sediment-free consortium. Clone libraries and denaturing gradient gel electrophoresis analysis of 16S rRNA gene community PCR products indicated the presence of uncultured alpha- and betaproteobacteria similar to those detected in contaminated, denitrifying environments. Cultures were incubated with H(34)-hexadecane, fully deuterated hexadecane (d(34)-hexadecane), or H(34)-hexadecane and NaH(13)CO(3). Gas chromatography-mass spectrometry analysis of silylated metabolites resulted in the identification of [H(29)]pentadecanoic acid, [H(25)]tridecanoic acid, [1-(13)C]pentadecanoic acid, [3-(13)C]heptadecanoic acid, [3-(13)C]10-methylheptadecanoic acid, and d(27)-pentadecanoic, d(25)-, and d(2)(4)-tridecanoic acids. The identification of these metabolites suggests a carbon addition at the C-3 position of hexadecane, with subsequent beta-oxidation and transformation reactions (chain elongation and C-10 methylation) that predominantly produce fatty acids with odd numbers of carbons. Mineralization of [1-(14)C]hexadecane was demonstrated based on the recovery of (14)CO(2) in active cultures.