A week after a high-profile paper suggested that the vast Deepwater Horizon oil plume could linger for months, another study claims bacteria are breaking the oil down quickly, and that the plume is likely gone.
The conflicts between the results are striking. Other researchers warn that there's just too little data to draw any conclusions. But the new findings are at least encouraging.
"We saw the same plume they did," said Terry Hazen, an ecologist and oil spill specialist at the Lawrence Berkeley National Laboratory, whose research is funded in part by BP. "We found that very large proportions of genes from water in the plume have the ability to produce enzymes that break down the oil."
As with last week's study, Hazen's involved samples taken from the deep-sea oil plume that in late June was 22 miles long, one mile wide and 650 feet thick, and was published in Science.
The previous study, led by researchers from the Woods Hole Oceanographic Institute, found few signs microbial activity around the oil. From those measurements, it seemed that months would pass before bugs broke down the oil.
The WHOI team didn't look directly at bacteria in the water, but used oxygen depletion -- caused by bugs multiplying and going into metabolic overdrive while eating -- as a sign of their activity.
By contrast, Hazen's team extracted microbial DNA from plume water samples, sequenced the genes and identified their functions. Many of the genes produce enzymes that break down some of the compounds in crude oil.
The researchers also identified a previously-unknown strain of ostensibly oil-gobbling Oceanospirillum that doesn't consume oxygen. Its activity would have gone unnoticed by the WHOI team.
"That particular species becomes dominant in the plume. It out competes some of the other bacteria that are normally present. It can break down the oil quite well," said Hazen, who noted that the Gulf's deep-sea microbes have evolved to handle crude oil that seeps naturally from the seafloor.
When Hazen's team put oil samples in a laboratory setup designed to mimic Gulf conditions, it had a half-life of between one and six days. And according to Hazen, the researchers have found no sign of the plume in the last three weeks, suggesting its breakdown.
But according to WHOI oceanographer Richard Camilli, the plume could already be hundreds of miles from its previous location, and Hazen's team could simply have missed it. "The plume is not a stationary object," he told the Wall Street Journal.
Other experts advised patience in interpreting the findings.
University of South Florida mircobial ecologist John Paul, part of a recent study that found oil in Florida fish spawning beds and contradicted federal claims of the oil's disappearance, wasn't convinced by the new results.
The differences in bacterial abundance, diversity and hydrocarbon degrading potential are "slight" between plume samples and regular Gulf seawater, said Paul. He also said that the gene-tagging technologies used by Hazen's team are used by few researchers "because they are often problematic in execution and interpretation of results."
According to University of Maryland aquatic toxicologist Carys Mitchelmore, Hazen's team only measured the breakdown of select compounds in the oil. "There's lots of other chemicals in the oil," she said.
She also stressed that it's essential to identify what happens when oil is degraded. That catch-all term implies that it just vanishes, but "sometimes things can be degraded into more toxic components," said Mitchelmore. The latest study did not make those measurements, nor did it test how microbes interacted with chemical oil dispersants used during the disaster.
"The big take-home is that we don't know much about many things related to this spill, the oil fate and its effects" said Mitchelmore. "There are huge data gaps and uncertainties, conflicting data from many aspects, and this will continue to happen based on the huge complexity of studying this."
"Above all," said Mitchelmore of the latest study, "note this is all based on 17 sample sites from the field."
Note: Funding for the study was provided by the Energy Biosciences Insitute, a joint project of the University of California, Berkeley, the Lawrence Berkeley National Laboratory, the University of Chicago at Illinois-Champaign and BP, who gave the EBI a $500 million, 10-year grant. Terry Hazen sits on the EBI's Executive Committee, as does BP executive Tom Campbell. Conflicts of interest are rarely as black-and-white or simple as they seem, but this ought to be mentioned.
Image: Bacteria at the edge of an oil droplet./Science.
See Also:
- Gulf's Depths Probably Still Clogged With Oil
- BP's 'Nightmare' Well: Internal Documents Uncover Negligence ...
- Better Oil Dispersant Tests Delayed in Gulf
- Gulf Coast May Be Permanently Changed by Oil Spill
Citation: "Deep-Sea Oil Plume Enriches Indigenous Oil-Degrading Bacteria." By Terry C. Hazen, Eric A. Dubinsky, Todd Z. DeSantis, Gary L. Andersen, Yvette M. Piceno, Navjeet Singh, Janet K. Jansson, Alexander Probst, Sharon E. Borglin, Julian L. Fortney, William T. Stringfellow,, Markus Bill, Mark S. Conrad, Lauren M. Tom, Krystle L. Chavarria, Thana R. Alusi, Regina Lamendella, Dominique C. Joyner, Chelsea Spier Jacob Baelum, Manfred Auer, Marcin L. Zemla, Romy Chakraborty, Eric L. Sonnenthal, Patrik D’haeseleer,4 Hoi-Ying N. Holman, Shariff Osman, Zhenmei Lu, Joy D. Van Nostrand, Ye Deng, Jizhong Zhou,, Olivia U. Mason. Science, published online, August 24, 2010.
Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.
