Andersen, Gary L.

Significance The Deepwater Horizon drilling accident was the first major release of oil and natural gases in the deep ocean, and considerable uncertainty remains about the fate of vast amounts of hydrocarbons that never reached the surface. We simulated the deep-sea plumes of dispersed oil microdroplets and measured biodegradation of crude oil components. We successfully reproduced the successive blooms of diverse bacteria observed in the field and obtained near-complete genomes of all major hydrocarbon-degrading species, providing an assessment of the metabolic capabilities of the microbial community responsible for biodegradation. Our results show that rapidly degraded components of oil were consumed by bacteria with highly specialized degradation capabilities and that crude oil alone could explain the microbial dynamics observed in the field.

DNA from low-biodiversity fracture water collected at 2.8-kilometer depth in a South African gold mine was sequenced and assembled into a single, complete genome. This bacterium, Candidatus Desulforudis audaxviator , composes >99.9% of the microorganisms inhabiting the fluid phase of this particular fracture. Its genome indicates a motile, sporulating, sulfate-reducing, chemoautotrophic thermophile that can fix its own nitrogen and carbon by using machinery shared with archaea. Candidatus Desulforudis audaxviator is capable of an independent life-style well suited to long-term isolation from the photosphere deep within Earth's crust and offers an example of a natural ecosystem that appears to have its biological component entirely encoded within a single genome.