Researchers say microbes likely consuming the oil from BP spill

Scientists have found evidence that a deep subsea plume of oil created by the BP well blowout is being consumed by bacteria that thrive in low temperatures and at the depths where the plume had formed. The research—which was funded indirectly by BP—could explain how millions of barrels of oil that spewed from the damaged well until it was capped in mid-July has apparently disappeared.

A research team led by Terry Hazen of Lawrence Berkeley National Laboratory (LBNL) announced on 24 August that it had identified a type of bacteria within a plume located at a depth of around 1100 meters. In an interview, Hazen says colleagues who have continued to monitor the plume found it increasingly difficult to track about two weeks after the BP well was capped on 15 July.

In the last three weeks they’ve been “unable to detect much of a signal at all,” he said, even with a search area that was expanded to 100 km from the wellhead to account for any drifting that might have occurred. Recent samples have turned up hydrocarbon concentrations in the parts per billion range, levels so minuscule that they might originate from natural seeps on the seafloor.

The LBNL findings are consistent with a controversial estimate that was prepared by the federal interagency National Incident Command (NIC) on 2 August that just one-quarter of the estimated 4.9 million barrels of oil that spewed from the BP well since the 20 April blowout remained in the waters of the Gulf.

Seawater samples taken from the plume by the LBNL group in late May and early June showed elevated quantities of a type of microbe, γ-Proteobacteria, relative to waters outside the plume. Those bacteria are known to degrade hydrocarbons, or to be stimulated by the presence of oil in cold environments. According to their paper , published online in Science on Tuesday, other signs of hydrocarbon biodegradation, including fatty acids and microbial genes, were also observed.

The article noted that the presence of γ-Proteobacteria would go undetected by the conventional method used to find evidence of biodegradation: depleted oxygen levels. That’s why a scientific team from the Woods Hole Oceanographic Institution didn’t spot evidence of bioremediation when they probed the plume in June.

In a paper published just days before Hazen’s, also in Science, the WHOI team stated, “The lack of systematic oxygen drawdown within the plume suggests that the petroleum hydrocarbons did not fuel appreciable microbial respiration on the temporal scales of our study.” The photo below shows a member of the WHOI team preparing to lower a sample collector.

But the microbial communities identified by the LBNL group not only break down hydrocarbons without consuming oxygen, they also thrive in the 5 °C environment found at the plume depth. Their presence indicates that the Gulf has evolved an intrinsic capability to remediate oil spills, says their paper.

The LBNL team was funded by the Energy Biosciences Institute, a consortium established at the University of California, Berkeley in 2007 with a 10-year, $500 million grant from BP. Hazen is a principal investigator in an ongoing EBI project that is exploring potential microbial roles in enhanced oil recovery. The University of Illinois at Urbana-Champaign and LBNL are also partners in EBI.

The infrared beamline at LBNL’s Advanced Light Source was utilized in the analysis of samples using Fourier-transform infrared spectromicroscopy. University of Oklahoma microbiologist Jizhong Zhou, inventor of a new technology known as the GeoChip for quickly and cheaply identifying functioning microorganisms in a scientific sample, was a contributor to the LBNL team.

In their paper, the WHOI scientists reported finding a plume of oil at least 35 km long, 2 km wide, and 192 m deep centered about 1100 m down, containing multiple hydrocarbons in concentrations greater than 50 μg/l. Oil in the plume was dispersed to the point where all samples were clear and odorless, although potentially still toxic to marine life.

Richard Camilli, who was the WHOI team’s chief scientist, said the plume was moving to the southwest at a rate of 6.5 km per day. “The data suggest that this plume extended much further than we tracked it,” he said, adding that the mission was cut short when a tropical storm approached. The WHOI scientists gathered their data on the plume over a 10-day period that ended in late June, and they have not returned to the Gulf since.

Many scientists had been skeptical of the NIC report’s findings. One assessment by the Georgia Sea Grant program complained that media reports had erroneously assumed that oil the federal report said was dispersed or dissolved had disappeared.

In fact, the GSG paper said, both dispersed and dissolved oil can remain highly toxic. The GSG also faulted the NIC’s inclusion in its calculations of the 17%, or 800 000 barrels (128 million liters), of oil recovered from the well by surface ships, which had never entered the Gulf. By its reckoning, GSG concluded that as much as 79% of the oil that was released into the sea from the well remains there, after taking into account the fraction that evaporated, or was biodegraded, skimmed, or burned.

The WHOI scientists were funded by three NSF rapid response grants, which bypass the standard peer-review process for projects in cases where data need to be collected urgently. As of 25 August, NSF has awarded a total of 132 of the so-called RAPID grants to investigators studying the impacts of the spill, with a total value of $15 million.

David Kramer