Biodegradation of petroleum hydrocarbons and related compounds in coastal marine sediments: Component concentrations, degradation rates, and microbial preferences

The consumption of hydrocarbons by microbes in marine sediments serves as an important element of the marine carbon cycle and is the focus of this dissertation. Three related studies were conducted, one assessing the broad molecular patterns of petroleum biodegradation in the deep subsurface, a second assessing patterns of aromatic hydrocarbon biodegradation in shallow sediments, and a third analyzing the role of volatile organic acids in methane-dominated sediments.;I applied advanced technology, comprehensive, two-dimensional gas chromatography (GCxGC), to address two major unresolved issues in the study of marine petroleum: the specificity of subsurface microbial communities for hydrocarbons during biodegradation and quantifying rates of aerobic hydrocarbon biodegradation with an emphasis on alkylated polycyclic aromatics (PAHs). Three important results arise. First, subsurface microbial communities were determined to possess a broad specificity for hydrocarbons, with evidence provided for the consumption of > 1000 compounds to varying extents. Second, results from GCxGC analysis of hydrocarbons extracted from an incubation time-series indicate that isomeric complexity may be the most important factor governing the rate of alkylated PAH oxidation. I find that oxidation rate constants for over 90 individual petroleum components were within an order of magnitude, ranging from 0.003 d-1 for the n-C38 to 0.031 d-1 for naphthalene. Third, results presented here indicate the existence of an inverse relationship between the number of alkyl-carbon substituents and the rate of PAH oxidation.;In the third study, I investigate the importance of short-chain volatile organic acids (VOAs) and their relation to microbial abundance and methane production and consumption. VOAs are important components of the dissolved organic carbon pool found within methanogenic sediments. Analysis of interstitial fluids extracted from sediments show that both acetate and formate are important microbial metabolites in this high flux, methanogenic locale and may be crucial to the transfer of energy between microbial communities. I discuss the relationship between organic acid concentrations, microbial abundance, and the flux of energy in the final chapters of this dissertation.