With the Deepwater Horizon spill finally choked off, researchers are hoping that marine microbes will help gobble up the millions of barrels of oil still lurking in the gulf. The first peer-reviewed study of the oil—published last week—suggested that the bugs weren't doing much, however, at least in the plume that was analyzed. But a study published today, which takes a look at the microbes themselves, finds that oil-eating bacteria are flocking to the spill in droves, though it's not clear how quickly they're digesting it.
Bacteria consume oil more or less the way humans metabolize butter, says oceanographer Richard Camilli of Woods Hole Oceanographic Institution in Massachusetts, the lead author on last week's report. They take in oxygen and hydrocarbons—the carbon-hydrogen molecules in the plume (which also appear in fatty foods like butter, margarine, and vegetable oil)—and spit them out as CO2 and biological waste. It's something they've been doing for millennia in the Gulf of Mexico. "With all of the seepage, including the 40 to 50 million gallons a year that seep naturally into the gulf, we'd have oceans covered with oil slicks if they weren't degrading," says Alan Mearns, a Seattle, Washington-based National Oceanic and Atmospheric Administration marine ecologist, who was not affiliated with either study. Researchers hope that this process, called biodegradation, can help break up the oil contaminating the gulf now.
To see if that is actually happening, a group of microbiologists from the University of California, Berkeley, pulled samples of seawater from a plume 1100 meters beneath the surface of the ocean—in the same location as one of the plumes detected by Camilli's team—and the uncontaminated area surrounding it. Led by microbiologist Terry Hazen of UC Berkeley, the team looked at water both inside and outside the plume, analyzing its chemistry, physics, and even the DNA of its inhabitants. The results, published online today in Science, offer some reassurance: Ocean bacteria are aware of the oily invasion of their territory, and they're responding accordingly.
Hazen's team found that microbes inside the plume samples were packed more than twice as densely as microbes outside it. Even more encouraging, the genes specifically geared to degrade hydrocarbons were more common in the plume as well, implying that it's not just general bacteria that are taking on the plume. All in all, Hazen's group predicts that, with the help of hungry microbes, the concentrations of the hydrocarbons his team analyzed in the plume could drop by half within a week.
But that doesn't mean the oil will be half gone in a week. The good news, according to Ronald Atlas, an oil microbiologist at the University of Louisville, Kentucky, is that the oil is definitely breaking up. "Microbes are clearly degrading the oil. The Hazen paper establishes that," says Atlas, who was not involved in the study. "The question to resolve between the two studies is, what are the real rates of degradation?"
Oil is made up of dozens of different hydrocarbon molecules. The ones Hazen analyzed—the alkanes—are generally the first to go, says Atlas. As for how long the rest will remain, it's unclear. It all depends on how stable the oil emulsion—the giant glob formed when oil and water mix—turns out to be. If it disperses easily, the bacteria shouldn't have much trouble. But if it holds together, Atlas says, they'll have a harder time breaking it apart.
Another concern has been that the oil-eating microbes could deplete oxygen within the plume. That's because the bacteria must extract oxygen from the water around them, which could spell disaster for local fisheries trying to get back on their feet. But neither study detected a dangerous drop in oxygen within the plume. "It would be very hard to establish a dead zone in this plume just because of microbial degradation," Camilli says.
Mearns sees reason for optimism. He says with Hazen's data and the rest of the data streaming in from elsewhere, scientists are now starting to think the oil will be gone much sooner than people thought before. "We're talking days to months."
This article has been revised. An earlier version said that bacteria survive the way humans would if they ate only butter.
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