Berkeley scientists have discovered a voracious species of primitive oil-eating bacteria that have largely consumed the huge deep-sea plume of dispersed oil fouling the Gulf of Mexico since the deadly BP Deepwater Horizon oil rig explosion in April.

As a result of the bacteria, the toxic plume that was once 22 miles long and more than 3,600 feet deep is now "undetectable," Terry C. Hazen, the chief microbiologist at the Department of Energy's Lawrence Berkeley National Laboratory, reported Tuesday.

For millions of years, bacteria have been eating oil that seeps from the sea floor, but Hazen and his colleagues discovered a particularly gluttonous form that multiplied rapidly in the months after the April 20 oil-rig explosion and spearheaded the plume's unexpected disappearance from the gulf's cold waters, Hazen said.

"We're still finding bacteria but no oil," Hazen said. "The plume is undetectable."

Because of their unique ability to consume oil swiftly, the bacteria should make a valuable tool against future oil spills that pose a threat to the environment, once they are firmly identified and cultured for what Hazen calls "bioremediation."

Oxygen consumption

The plume was created by a chemical dispersant called Corexit 9500 that BP dumped around the wellhead after its oil rig exploded in an effort to break up the torrent of crude oil gushing from the seabed. The plume continued spreading through the water even after the underwater gusher was finally plugged July 15.

The spreading plume had aroused fears that it could devastate the marine ecology in the gulf because many oil-eating bacteria consume oxygen as well as hydrocarbons - a process that could produce "dead zones" of life-threatening oxygen depletion. But the newly found microbes devour the microscopic droplets with far less depletion of oxygen than other oil-eating bacteria, Hazen and his lab colleagues reported.

Hazen and his team report on the new microbes in the online journal Sciencexpress on Thursday.

Just last week, scientists at the Woods Hole Oceanographic Institution on Cape Cod reported that their data, gathered by their autonomous underwater detectors in June, showed the plume was breaking up so slowly it could threaten sea life for months to come. The Woods Hole scientists, headed by oceanographer Richard Camilli, also reported their findings in Sciencexpress.

"These new findings on the plume's rapid degradation will be extremely helpful for us to learn more about the natural processes that can degrade oil so rapidly in the sea," Camilli said Tuesday in an interview.

He pointed out, however, that some of the plume's microscopic oil particles are being diluted naturally in the seawater, while other organisms are playing a role in consuming varied chemical molecules in the plume's hydrocarbons.

Thriving in cold water

The bacteria were discovered by Hazen's team working aboard research vessels leased by BP. From May to June, the scientists visited 17 sites to collect more than 200 samples of the plume at depths of between 3,600 and 4,000 feet.

The team found the new species in a class of microbes particularly adapted to thrive in cold water and known as gamma-proteobacteria. The species degrades oil much faster than biologists had expected, Hazen reported.

The group's work is supported by part of the $200 million grant that BP gave to an environmental research project jointly run by UC Berkeley, Hazen's team, the Berkeley lab, and the University of Illinois.

"We're a Department of Energy national lab," Hazen said, "and our work is completely independent of any funding source."