On the hunt for life in an oil spill

UNC researchers plumb the plume for minuscule organisms that gather to dine on the oil

CorrespondentJune 14, 2010 

  • Identifying organisms only 1micron in size isn't easy, even in a small sample of water. Researchers use a vacuum pump to pull the water through a fine filter. A preservative solution is then added to fix the cells. They then use genetic staining to test for pre-identified gene sequences, which will glow under certain conditions. If the microbes they're testing for are present, researchers can count them right on the filter.

  • Andreas Teske

    Title: Microbial ecologist, UNC-Chapel Hill

    Specialty: Extreme deep-sea environments

    Why it's interesting: "There happen to be active seep fields where you have petroleum-rich fluids, methane-rich fluids migrating up from the deep subsurface until they reach the sea floor. Lots of microbial mats are growing; you have interesting mineral formations, carbonates. It's very different and immediately visually different from the surrounding sea floor, which is just bare Atlantic sediment."

In the midst of the largest oil spill in U.S. history, scientists from UNC-Chapel Hill are scouring the Gulf of Mexico for an almost invisible life-form that may be crucial to the cleanup.

Marine microbiologist Andreas Teske and his team are hunting for a group of microbes that feed on oil, breaking down the hydrocarbons into carbon dioxide.

Since the Deepwater Horizon sank in an explosion that killed 11 crew members April 20, the severed wellhead underneath has spewed millions of gallons of oil into the Gulf.

Luke McKay, one of Teske's doctoral students, was aboard one of the first research vessels to reach the site 35 miles off the coast of Louisiana. He said evidence of the spill was already clear.

Suddenly, "You see the wake of the boat become red," McKay said. "We were going through what should be blue-green beautiful waters, and they become bright red because of the contaminants."

McKay and other UNC-CH researchers have taken hundreds of samples of everything from surface water to the sediment 5,000 feet below.

What they've found so far indicates the microbes are already munching away at the oil - and they're dining in some unexpected places.

"It can also be viewed as something encouraging," Teske said. "Microbial degradation of the oil has already started, even if we haven't done anything to promote it yet."

Hijacked by the spill

Oil-consuming microbes are naturally present in the water column, even in extreme marine environments on the sea floor. They're opportunists, flourishing when their preferred food supply is available. Most of the time, the dinner bell only rings where petroleum gradually seeps from fissures in the seabed.

"The entire [Gulf] Coast of depths of 600 to maybe 2,000 meters is a kind of Swiss cheese with lots of natural hydrocarbon springs," Teske said.

One of these sites, called Mississippi Canyon 118, is located about 3,000 feet below the surface on the continental slope and is one of Teske's regular stomping grounds.

"It looked like we could continue this [research] peacefully and undisturbed, when all the sudden the Deepwater Horizon oil spill occurred only nine miles southeast of this location," Teske said. "Everything got redirected."

That included McKay. He had spent the past week driving a truck full of gear cross-country after an expedition off the California coast. He made it to Atlanta before he got the call from his adviser: The R/V Pelican was shipping out in less than 24 hours. He couldn't refuse.

But the quick turnaround presented a challenge because research cruises typically take months to plan - not days. The team used rapid response grant funding and shipped supplies down to the dock at Cocodrie, La. Team members also had to think on their feet.

"This was thrown together so quickly," McKay said. "Some of the samples I was taking, I was taking in Gatorade bottles - just anything we could get our hands on to take samples."

McKay spent five days aboard the ship taking samples of surface water and sediment as close as 1,600 feet from the spill. He also used buckets to scoop oil from the tarry rivers formed in the sea. Some samples returned with him to the Chapel Hill lab, while others will be analyzed by partner universities.

"That was the overarching theme of this cruise: Take whatever you can get and it probably will be used by someone, somewhere, sometime," he said.

Although the scientists on the Pelican didn't have the resources to test the effect of the spill on the entire water column, researchers on the R/V Walton Smith did.

The murky layer

The crew, which returned last week, collected water samples at multiple depths and measured murkiness and oxygen levels.

Normally, conditions at different depths don't change quickly below the surface layer. But that wasn't the case near the spill, where readings showed a murky band suspended in the water column between about 3,000 and 4,000 feet.

That murky layer corresponds with a dramatic dip in the level of oxygen, which oil-consuming microbes use to digest their meals.

"Microbial processes in the water column are already consuming the hydrocarbons in the oil, and of course, consume oxygen when doing so," Teske said.

Scientists have concluded that a large amount of emulsified oil has formed a plume at these depths. Tiny petroleum droplets have achieved neutral buoyancy with the seawater around them, halting their ascent in the water column.

"The oil is not homogenous," Teske said. "It's a complicated chemical mixture - some components that are lighter than water, some components that are heavier."

The path that leads north

At those depths, seawater density is hard to change, meaning the oil isn't likely to sink or rise. But deepwater currents could carry the plume horizontally around the coast of Florida and up to North Carolina before the Gulf Stream pulls it out to sea.

Even with complex equipment, the rapidly changing plume is hard to track.

"When we revisited sites, the readings would change. The circulation around that area also changes, so we believe the plume is also moving," said Lisa Nigro, one of Teske's graduate students who was aboard the Walton Smith. "You either hit it or you don't."

The danger to marine life is relatively unknown. Teske said the microbes eating oil don't produce harmful byproducts. But extremely rapid growth - and increased carbon dioxide production - could cause an oxygen-depleted environment similar to the dead zone near the mouth of the Mississippi River. But he said oxygen readings aren't anywhere near that low now.

"It's hard to tell what happens at these depths. The oil is finely dispersed, but probably still toxic," Teske said. "It's not something I'd want to swallow, or if I was a fish, something I'd want to pump through my gills."

A hunt for 'usual suspects'

What Teske and his team can determine, however, are the hydrocarbon connoisseurs actually present in the Gulf - and how long they may take to process the contamination.

Once back in the lab, McKay began work to finely filter his water samples for microbes. He'll use genetic staining to ID specific groups of well-catalogued oil-consuming organisms - the ones he calls "the usual suspects."

From there, Teske's researchers can figure out what stimulates the microbes and the state of the oil after digestion.

Other scientists may use this information to help craft a clean-up strategy. For example, one technique with much smaller oil spills on land, like jet-fuel-contaminated airfields, is to aerate them with oxygen and kick-start the bacterial feast. But that could backfire if the organisms are fertilized too much, creating a deadly anoxic environment.

Regardless of the technique, Teske said, it's likely we'll have to rely on organisms 1 micron in size to fix one of the planet's worst ecological disasters.

"At a certain level, our toolbox is exhausted, and one has to leave it to Mother Nature and her micro-organisms," Teske said. "But it will take time."

Tyler Dukes: tyler.dukes@gmail.com

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