Microbial metabolism of hydrocarbons under methanogenic conditions

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Anaerobic microorganisms are now known to be key catalysts of hydrocarbon biodegradation. The current knowledge of anaerobic hydrocarbon metabolism comes mainly from studies conducted under nitrate- or sulfate-reducing conditions, while comparatively little is known in methanogenic environments where such electron acceptors are limited. These environments can include polluted drinking water aquifers and economically important oil reservoirs. Methanogens are a specialized group of microorganisms that utilize only a few simple compounds such as acetate or hydrogen/carbon dioxide to form methane. Thus, hydrocarbon bioconversion to methane requires the participation of other species that can enzymatically activate a hydrocarbon and metabolize it to methanogenic precursors. Currently, the hydrocarbon activation mechanisms, the ensuing metabolic pathways, and the hydrocarbon-activating microbial species involved in the interspecies interaction with methanogens are largely unknown. The proposed work will provide much needed fundamental information regarding methanogenic hydrocarbon metabolism through two major objectives (1) identifying metabolites produced during the methanogenic metabolism of model monoaromatic hydrocarbons, alkanes, and polycyclic aromatic hydrocarbons through chemical analysis and catabolic gene probing, and (2) identifying key anaerobic microbial species involved in the bioconversion of hydrocarbons through the isolation of methanogens, directed cultivation of eubacteria, and molecular biology methods including nucleic acid-based stable isotope probing. Through this work, key organisms and biochemical pathways of methanogenic hydrocarbon metabolism will be identified. Understanding methanogenic hydrocarbon metabolism has important ecological, economic, and energy-related applications in Canada with respect to the restoration of fuel-contaminated drinking water aquifers, how methanogenic consortia convert light oil to lower-value heavy oil in reservoirs, and how such consortia may be used in situ to generate clean-burning natural gas from oil remaining in marginal reservoirs as a "green" energy recovery biotechnology.