Rapid microbial respiration of oil from the Deepwater Horizon spill in offshore surfacewaters of the Gulf of Mexico

Abstract

The Deepwater Horizon oil spill was one of the largest oil spills in history, and the fate ofthis oil within the Gulf of Mexico ecosystem remains to be fully understood. The goal ofthis study—conducted in mid-June of 2010, approximately two months after the oil spillbegan—was to understand the key role that microbes would play in the degradation of theoil in the offshore oligotrophic surface waters near the Deepwater Horizon site. As theutilization of organic carbon by bacteria in the surface waters of the Gulf had beenpreviously shown to be phosphorus limited, we hypothesized that bacteria would be unableto rapidly utilize the oil released from the Macondo well. Although phosphate wasscarce throughout the sampling region and microbes exhibited enzymatic signsof phosphate stress within the oil slick, microbial respiration within the slickwas enhanced by approximately a factor of five. An incubation experiment todetermine hydrocarbon degradation rates confirmed that a large fraction of thisenhanced respiration was supported by hydrocarbon degradation. Extrapolating ourobservations to the entire area of the slick suggests that microbes had the potential todegrade a large fraction of the oil as it arrived at the surface from the well. Theseobservations decidedly refuted our hypothesis. However, a concomitant increase inmicrobial abundance or biomass was not observed in the slick, suggesting thatmicrobial growth was nutrient limited; incubations amended with nutrients showedrapid increases in cell number and biomass, which supported this conclusion.Our study shows that the dynamic microbial community of the Gulf of Mexicosupported remarkable rates of oil respiration, despite a dearth of dissolved nutrients.