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    Bacteria ate away at gulf oil plume, study shows

    Findings verify government spill statistics
    By David Brown, Washington Post  |  August 25, 2010

    WASHINGTON — The Gulf of Mexico ecosystem was ready and waiting for something like the Deepwater Horizon blowout and seems to have made the most of it, a new scientific study suggests.

    Petroleum-eating bacteria, which had dined for eons on oil seeping naturally through the seafloor, proliferated in the cloud of oil that drifted underwater for months after the April 20 accident. They not only outcompeted fellow microbes, they each ramped up their own internal metabolic machinery to digest the oil as efficiently as possible.

    The result was a nature-made cleanup crew capable of reducing the amount of oil in the undersea plume by half about every three days, according to research published online yesterday by the journal Science.

    The findings, by a team of scientists led by Terry C. Hazen of Lawrence Berkeley National Laboratory, in California, help explain one of the biggest mysteries of the disaster: Where has all the oil gone?

    “What we know about the degradation rates fits with what we are seeing in the last three weeks,’’ Hazen said. “We’ve gone out to the sites and we don’t find any oil, but we do find the bacteria.’’

    The findings point to a different conclusion from that drawn by many readers of a study published last week, also in the journal Science. That research, by scientists at Woods Hole Oceanographic Institute, found no reduction in the oxygen content of the gigantic oil plume, suggesting that microbes were consuming the oil very slowly.

    The study published yesterday also suggests indirectly that dispersants used to break the wellhead stream of oil into a mass of submicroscopic particles may have sped the cleanup. By increasing the surface area between oil and water, the dispersants seem to have provided the deep-sea microbes greater access to this unusual food source.

    Some of the spill’s 206 million gallons of oil have come ashore, some have sunk into bottom sediments, and a little is still a floating froth. But the mile-wide, 650-foot high cloud of oil that drifted for months 4,000 feet below the surface seems to have disappeared in the six weeks since the well was plugged.

    The plume’s whereabouts have been a contentious matter.

    In the Woods Hole study published last week, scientists described finding an undersea oil cloud on June 23 to 27 similar to the one Hazen and his colleagues found between May 25 and June 2, which was similar to one found soon after by people from Monterey Bay Aquarium Research Institute.

    But earlier this month, two weeks after the well was plugged July 15, scientists from the federal government argued that half the oil was gone from the water and the rest was disappearing fast. That assertion was viewed as unreasonably rosy by many specialists.

    However, Hazen’s calculation of the speed with which bacteria consumed the oil — combined with his recent findings that oil can no longer be detected in deep gulf waters — supports the credibility of all those positions.

    “We were all right,’’ he said.

    In the new study, the Berkeley research team took water samples inside and outside the oil plume. The samples were analyzed for oil, bacteria, complex compounds such as fats, building-block chemicals such as nitrogen and phosphorous, and dissolved oxygen.

    Inside the plume there were about twice as many bacterial cells per milliliter of water as outside it. There was also twice as much “phospholipid,’’ a type of compound in cell membranes. Both findings pointed to an oil plume teeming with life. In fact, the researchers detected 951 different subfamilies of bacteria containing in all more than 10,000 distinct species. Sixteen of those 951 subfamilies were especially abundant in the plume samples compared with samples outside the plume. They were of a type called gamma-Proteobacteria, known for degrading oil-like substances in cold water.

    The scientists then looked at the roughly 5,000 genes active in the bacteria. They found that the 1,600 genes involved in “hydrocarbon degradation’’ were cranked up to much higher concentrations in the plume bacteria than in the bacteria outside it.

    From a purely Darwinian point of view, this was no surprise. About 500,000 barrels of oil get into the gulf’s water each year through seafloor seeps. Natural selection has favored microbial species able to quickly use oil as a nutrient. It has particularly favored ones that can use it in very cold, bottom waters — conditions generally not conducive to rapid bacterial growth.

    © Copyright 2010 The New York Times Company

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