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Role of bacteria in Gulf oil spill under the microscope

ISS.OilSpoll.jpgSince last year’s Deepwater Horizon oil spill in the Gulf of Mexico, microbiologists have been working to understand how the microbial environment responds to and ultimately breaks down oil from a spill. (For more information, see our feature on the topic.) This weekend at the 111th general meeting of The American Society for Microbiology in New Orleans – the nearest large city to the spill site – an entire session was dedicated to the newest results from spill studies.

Here’s an overview of what came out of the plenary session held on 22 May:

David Valentine, a geomicrobiologist at the University of California, Santa Barbara, showed that the motion of deep water in the Gulf boosted oil-eating microbes’ ability to break down oil spurting from the well. Using a model of the deep water plumes developed with UC Santa Barbara colleague Igor Mezic, Valentine showed that water sitting over the leaking oil well was first carried away, bringing with it oil and blooming microbes. Then those waters, teeming with bacteria prepped to devour oil, were carried back over the well where more oil flowed in. The result was pulses of accelerated oil biodegradation as waters were circulated around. Valentine says the model is helping understand how rapidly the oil and gas were consumed.

“It’s very difficult to get down there and study what happened a year ago nearly a mile deep in the ocean,” says Valentine. “By understanding the fundamentals of what was controlling where the oil went and how long things were exposed to it, I think we’re one step closer to understanding the damage.”

Microbial ecologist Terry Hazen, head of the ecology dept at Lawrence Berkeley National Laboratory in Berkeley, California, led a team of about 50 scientists that analyzed the microbial communities in ocean waters contaminated by oil. They found completely different oil-degrading microbe species at depths of 1000-1500 meters compared to those within 150 meters of the surface. Moreover, the microbial communities that had bloomed in the presence of oil stuck around even after the oil had been degraded.

In future, those microbial signatures could help track recent oil releases, says Hazen. “Even when can’t see the oil, we can see this microbial community change to suggest oil had been present in the recent past.”

Microbiologist Joel Kostka and biogeochemist Markus Huettel of Florida State University in Tallahassee have been studying the fate of the oil that washed ashore on Pensacola Beach and St. George Island in Florida. They have found that many species of bacteria, including 24 that are related to oil-munching varieties, bloomed when the oil hit. Those bacteria broke down the oil, in the process consuming a lot of the water’s oxygen. One of the team’s goals is to identify sentinels of oil contamination, species that predominate in fresh oil vs. degraded oil, in hopes of one day being able to use extracted DNA from sand to figure out which contaminants are there. “It would be a lot easier to profile the microbial community than it is to analyze the petroleum hydrocarbons,” says Kostka. “It’s potentially a cheaper and easier way to determine the extent of contamination.”

The team is also investigating the effects of BP’s efforts to clean up beach oil and whether or not such efforts are a good idea in the future. And they are looking at the extent to which the oil has blocked oxygen and nutrients from getting to diverse microbes that recycle organic matter in the shallow ocean, which could have impacts on the nutrients feeding phytoplankton at the base of the food chain, Kostka says.

Efforts to understand the oil’s effects on the largest marine mammals down to the smallest microscopic organisms are crucial, says Samantha Joye, a biogeochemist at the University of Georgia in Athens. There could be impacts years down the road for which data gathered today will provide predictions and answers, she adds.

“This is an incredible insult to the ecosystem,” she says. “If we don’t understand what the impacts are, we’re not going to be able to evaluate what the recovery trajectory is.”

Image: Last year’s Gulf oil spill as seen from the International Space Station. Mississippi delta visible at upper right. NASA.


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