Potential for oil hydrocarbon biodegradation by microbial communities in marine environments

In 2010 the Deepwater Horizon spill released 4.9 million barrels into the Gulf of Mexico before being contained in September of that year.The native microbial community degraded petroleum in the water column, and a variety of hydrocarbon-degrading microorganisms were present in the deep-sea plume. In the years following the DWH spill (2011-present), there have been 1,917 reported spill or contamination events resulting in more than 2,989,675 barrels of petroleum released into the environment. Traditional methods for cleaning up petroleum spills are expensive in efficient; bioremediation (i.e., biodegradation by microorganisms) of petroleum can be effective while having minimal additional adverse affects on the environment. However, environmental variables such as temperature, oxygen concentration, and available nutrients impact the rate and extent of microbial biodegradation of petroleum. This dissertation examines microbial communities in six marine basins around the world with particular attention to the petroleum degrading sub-population to determine the potential for oil biodegradation in each basin. Oil degrading bacteria were ubiquitous in all six marine environments. The Eastern Atlantic receives nutrient enrichment from the Angola-Benguela Front, which is likely to facilitate oil biodegradation in that basin. Microcosm experiments were conducted to investigate the effect of oxygen amendment to communities from hypoxic environments, which one might expect to enhance oil biodegradation. Most of the individual oil hydrocarbons were degraded more efficiently in anoxic microcosms. Anoxic microcosms degraded a larger proportion of the shorter aliphatics (< 22 carbons; including branched aliphatics, e.g., pristane and phytane) than oxic microcosms. Conversely, oxic microcosms more completely degraded most of the longer aliphatics (≥ 22 carbons). Anoxic microcosms were similar to or exceeded oxic microcosms in the degradation of all aromatic hydrocarbons. When the communities are exposed to oxygen, aerobic organisms may grow rapidly on labile carbon and dominate the community, limiting overall oil biodegradation. On the other hand, these effects would be limited under anoxic or hypoxic conditions. These results suggest that deep water communities in the Caspian Sea are adapted for better oil biodegradation under anoxic or hypoxic conditions when compared to oxic conditions.

Portions of this dissertation are published in the journal Frontiers in Microbiology.