Oil-derived marine snow formed at the sea surface and sank to the seafloor following Deepwater Horizon. Previous studies observed the response of microbial communities in soft-bottom sediments using samples collected at a single time point or within short time frames. This study complements previous research with a long-term timeline survey of these microbial communities. The researchers obtained sediment samples near the Macondo wellhead in May 2010, September 2010, mid-October 2010, late-November 2010, and July 2011. They then derived and analyzed near-complete 16S rRNA gene clone libraries for bacteria extracted from the samples.
The May 2010 samples served as controls because they did not exhibit signs of marine snow deposition, including discoloration, visible floc, hydrocarbon or sulfide smells, or metal signatures related to altered geochemical conditions. September 2010 samples contained floc-like hydrocarbon-smelling deposits. The mid-October 2010 samples had elevated petroleum concentrations and a distinct red-brown coloration in the upper 3 – 4 cm (indicative of redox). Late-November 2010 and July 2011 samples had a the red-brown surface layer, but no hydrocarbon smell, indicating the loss of volatile compounds.
Cycloclasticus, a genus of a PAH-degrading bacteria reported in Deepwater Horizon-related surface slicks, deep plume, and post-plume deep water, were present in the fall 2010 samples. Roseobacter bacteria, which may play an important role in alkane and PAH degradation, were also abundant in the September 2010 samples. The October 2010 samples exhibited a sharp increase in sulfate-reducing anaerobic Deltaproteobacteria. Increased abundances of PAH-degrading bacteria coincided with the marine oil snow sedimentation event, suggesting that marine snow likely transported the bacteria to the seafloor.
Seafloor microbial populations responded to the marine snow fallout in waves of physiologically and evolutionarily different microbial groups that successively degraded hydrocarbons. Study author Andreas Teske explained, “Some of these microbial players are indigenous to the seafloor sediments in the sense that they are never found in the water column. Others appear to be equally at home on the seafloor and in the oil-contaminated marine snow particles that sank through the water column. Finally, some of these particle-associated microbes are not native to sediments but appear to hitch a ride down to the seafloor.”
According to Teske, further analysis identified some previously unknown hydrocarbon-degrading bacteria. “The catalogue of known oil-degrading bacteria appears to be surprisingly incomplete. The ‘usual suspects’ are limited to relatively few bacterial species and genera that have been studied in the lab,” he said. “As soon as you compare these well-studied oil degraders with those populations that are responding strongly to the oil spill in nature, it becomes clear that many microbial oil degraders have not been cultured and studied at all.”
Data for this study are publicly available through the Gulf of Mexico Research Initiative Information and Data Cooperative (GRIIDC) at doi:10.7266/N7RF5S21.
This research was made possible in part by a grant from the Gulf of Mexico Research Initiative (GoMRI) to the Ecosystem Impacts of Oil and Gas Inputs to the Gulf-2 (ECOGIG-2) consortium. Other funding sources included the National Science Foundation (RAPID Response: the microbial response to the Deepwater Horizon Oil Spill; NSF-OCE 1045115).
The Gulf of Mexico Research Initiative (GoMRI) is a 10-year independent research program established to study the effect, and the potential associated impact, of hydrocarbon releases on the environment and public health, as well as to develop improved spill mitigation, oil detection, characterization and remediation technologies. An independent and academic 20-member Research Board makes the funding and research direction decisions to ensure the intellectual quality, effectiveness and academic independence of the GoMRI research. All research data, findings and publications will be made publicly available. The program was established through a $500 million financial commitment from BP. For more information, visit http://gulfresearchinitiative.org/.
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