Award: OCE-1045115

1) Microbial community succession in the Gulf of Mexico after the oil spill. We have shown a distinct community succession of hydrocarbon-degrading bacteria in the water column of the Gulf of Mexico, near the Macondo wellhead. The oil spill completely reorganized microbial carbon processing and microbial community structure; as the most conspicuous oil-spill-related bacteria, members of the genus Cycloclasticus and the Oceanospirillales dominated water samples during the early oil spill stages before disappearing in the months after the oil spill.

(A) Mixtures of fresh crude oil and sea-water (such as those occurring at the sea surface) are colonized, already at an early stage (May 2010), by aromatic-degrading members of the genus Cycloclasticus. These bacteria are indigenous to the Gulf of Mexico, and in many other marine habitats with hydrocarbons present.

(B) Members of the Oceanospirillales dominate the deep-water hydrocarbon plume at ca, 1100 to 1300 m depth near the wellhead almost entirely, at least until the end of May 2010 (sampled May 31 2010). These bacteria are not available in culture, and their detailed metabolism and carbon source is therefore uncertain; their closest cultured relatives specialize in oxidation of unbranched alkanes, a major component of petroleum hydrocarbons. They are no longer detected after approx. mid-June 2010, possibly reflecting the microbial consumption of the deepwater hydrocarbon plume, consisting of highly volatile alkanes.

(C) In June, the Oceanospirillales community yields to other genera of hydrocarbon-degrading bacteria and common marine heterotrophs (Cycloclasticus and Colwellia); this marks the transition to a microbial community that also degrades the biomass produced by the oil spill, no longer only the petroleum compounds itself.