| Marine hydrocarbon seeps emit oil and gas into the marine environment, where they are subject to oxidation by microbes. To identify responsible organisms and characterize these processes, a combination of culture, culture-independent, and chemical techniques were applied. Stable isotope probing (SIP) was used to show that the primary consumers of 13C methane in seep sediment were Gammaproteobacteria from the family Methylococcaceae, Gammaproteobacteria related to Methylophaga, and Betaproteobacteria from the family Methylophilaceae, though the latter two groups may have been cross-feeding on methanol. 13C ethane was consumed by a novel group of Methylococcaceae and a highly divergent methane monooxygenase-like gene was detected in the 13C-labeled DNA, which may encode an ethane monooxygenase. 13C propane was consumed by a group of unclassified Gammaproteobacteria not previously linked to propane oxidation.;In addition to SIP, four strains of aerobic ethane, propane, and butane oxidizing bacteria- Pseudomonas stutzeri strains MR2, MR3, and MR4, and Rhodococcus sp. MR32- were isolated from seep sediment. Each isolate contained genes for propane monooxygenase, alkane hydroxylase, and cytochrome P450, and they were capable of growth on many compounds, including n-alkanes, alcohols, carboxylic acids, sugars, and crude oil. Two-dimensional gas chromatography was used to assess the extent of degradation for 211 compounds in crude oil. The isolates most extensively degraded n-alkanes, but n-alkylcyclohexanes and pentanes, alkylbenzenes, naphthalene, methylnaphthalenes, phenanthrene, and dibenzothiophene also showed moderate to heavy degradation. Low degradation was observed in most cyclohexyl isoprenoid alkanes, C1-C3 dibenzothiophenes and <C20 branched alkanes. Low to moderate degradation also occurred with some C2 and C3 naphthalenes, C1 and C2 phenanthrenes, and C1-C3 dibenzothiophenes. In comparison to these isolates, the hydrocarbon specialist Alcanivorax borkumensis showed a similar capacity for n-alkane degradation, but more heavily degraded the branched alkanes. A. borkumensis also showed heavy degradation of alkylcyclohexanes and alkylcyclopentanes, but did not consume most aromatic compounds. These differences may explain how these organisms fill different ecological niches, with A. borkumensis blooming rapidly after an oil spill, while others persist over longer time periods by degrading a wider range of compounds. |
