The results are among the first in what is expected to become a deluge of studies on the Gulf oil spill. By offering data on how fast microbes consume oil, the results could be useful in helping scientists to determine what happened to the oil and how the oil could affect marine life.
In addition, the results also suggest that most of the microbes in the cloud are a new species that do not significantly deplete oxygen in the water as they consume the oil.
The work represents "the first insight into the organisms that are involved" in degrading oil clouds in the Gulf oil spill, says David Valentine, a microbiologist at the University of California at Santa Barbara who has long studied the undersea microbes as underwater cleanup crews for oil.
The microbiology analysis is "very, very good," says Dr. Valentine, who was not part of the team, which reported its results in an early release by Science Express.
Second study in two weeks
This latest research follows another look at the same plume of highly diluted oil droplets, released last Thursday.
Both groups found some similarities: They put the plume at roughly the same depth, and they recorded similar, very low concentrations of key hydrocarbons – roughly the equivalent of 9 gallons of hydrocarbons for every million gallons of sea water.
They also both detected only a light dip in oxygen levels compared with water outside the plume. In that way, the studies attempted to tackle a question raised by many marine scientists: To what degree would microbial activity create a mass of relatively low-oxygen water, which could affect bottom-dwelling creatures in certain areas of the Gulf?
The study released last week, led by scientists with the Woods Hole Oceanographic Institution, inferred that bacteria had not broken down the oil appreciably, based on oxygen measurements. The team collected its measurements during a nine-day cruise that started June 19.
At the time, the plume stretched at least 22 miles southwest of the Deepwater Horizon blow-out site.
In the study released Tuesday, however, scientists from the Lawrence-Livermore National Laboratory and the University of the Pacific came to a different conclusion about how quickly microbes were breaking down the oil.
The team focused its efforts on exploring how the type and number of microbes varied inside and outside the plume. The team sampled the microbe population within and around the plume between May 25 and June 2, when it stretched to about 10 miles from the well site.
Genetic analyses of the microbes brought back in water samples indicate that the vast majority of the gene sequences from within the plume belonged to a new species of oil-degrading microbe. The team calculates that the microbes could degrade half the oil they are exposed to in 1.2 to 6.1 days.
The team's results suggest that oil degradation could occur faster than many researchers have anticipated. Indeed, team leader Terry Hazen, who heads the ecology department at the Lawrence-Berkeley National Laboratory, says: "For the last three weeks we have not been able to see that deep-water plume."
Dr. Valentine, who lauds the microbiology work, cautions however that the team may have gone too far in inferring the high pace of degradation.
For instance, he says, in the lab the team "fed lots of oil to the newly discovered organism, supercharged them, then asked the question: How fast are they consuming oil. It's not surprising you can get them to do that quickly when you supercharge them."
"They do show that there's a native capacity" to consume a relatively large amount of oil, "but how fast it happens is one of the big questions," he says adding that it's unclear if the microbes at depth have been supercharged by the oil they've consumed.
The question of the pace of biodegradation may be one of the toughest questions to answer, Valentine says. For many measurements, techniques are fairly standard from one research group to the next. Over time, individual research-cruise snapshots of data can be converted to flip books, showing how conditions change with time.
But some methods – including those for estimating the pace at which biodegradation takes place – vary from one team's cruise to another's cruise.
Scientists are "out there using a one-of-a-kind tool or techniques they've developed over their careers," making it difficult for different groups to make similar measurements from cruise to cruise, he says.