Anaerobic Biodegradation of n -Hexadecane by a Nitrate-Reducing Consortium

Abstract

ABSTRACT 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 β-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.