August 25, 2010

New, Fast-eating Microbe Devoured Gulf Oil: Study

A massive oil plume deep in the Gulf of Mexico created by BP's broken Macondo well has been consumed by a newly-discovered species of microbes, according to a study by scientists with the Lawrence Berkeley National Laboratory.

The spill had spewed a vast oil plume at a depth 3,600 to 4,000 feet, extending roughly 10 miles out. 

Scientists now believe it was the oil itself that stimulated the fast-eating microorganisms to degrade the hydrocarbons.  In fact, these new and unclassified species of proteobacteria were so efficient that the plume is now virtually undetectable, said Terry Hazen of Lawrence Berkeley National Laboratory, who led the study.

Furthermore, the degradation appears to have taken place without a significant level of oxygen depletion.

"Our findings show that the influx of oil profoundly altered the microbial community by significantly stimulating deep-sea psychrophilic (cold temperature) gamma-proteobacteria that are closely related to known petroleum-degrading microbes," said Hazen, a microbial ecologist with Berkeley Lab's Earth Sciences Division and principal investigator with the Energy Biosciences Institute.

"This enrichment of psychrophilic petroleum degraders with their rapid oil biodegradation rates appears to be one of the major mechanisms behind the rapid decline of the deepwater dispersed oil plume that has been observed."

The uncontrolled oil blowout from BP's well was the deepest and one of the largest oil spills in history.  The extreme depths in the water column and the magnitude of this leak presented a number of challenges.

To prevent large amounts of the highly flammable crude from reaching the surface, BP deployed an unprecedented amount of the commercial oil dispersant COREXIT 9500 at its wellhead, creating a plume of tiny petroleum particles.

Although the environmental effects of COREXIT have been studied in surface water for years, its effectiveness and potential impact on the Gulf marine ecosystem were unknown.

Hazen and his colleagues analyzed microbial genes in the dispersed oil plume, which revealed a variety of hydrocarbon-degraders, some of which were strongly correlated with the concentration changes of various oil contaminants.

An examination of changes in the oil composition as the plume expanded from the wellhead indicated faster-than-expected biodegradation rates.

"Our findings, which provide the first data ever on microbial activity from a deepwater dispersed oil plume, suggest that a great potential for intrinsic bioremediation of oil plumes exists in the deep-sea," Hazen said.

"These findings also show that psychrophilic oil-degrading microbial populations and their associated microbial communities play a significant role in controlling the ultimate fates and consequences of deep-sea oil plumes in the Gulf of Mexico."

Hazen and his colleagues began their study in May, when the extreme depths of the Gulf were an unexplored microbial habitat under enormous pressure and temperatures of around 5 degrees Celsius.  There is normally little carbon present.

"We deployed on two ships to determine the physical, chemical and microbiological properties of the deepwater oil plume," Hazen said.

"The oil escaping from the damaged wellhead represented an enormous carbon input to the water column ecosystem and while we suspected that hydrocarbon components in the oil could potentially serve as a carbon substrate for deep-sea microbes, scientific data was needed for informed decisions."

The researchers analyzed more than 200 samples collected from 17 deepwater sites between May 25 and June 2, 2010.  Sample analysis was enhanced by the use of the Berkeley Lab PhyloChip "“ a unique DNA-based microarray that can be used to quickly, accurately and comprehensively detect the presence of up to 50,000 different species of bacteria and archaea in a single sample from any environmental source, without the need of culturing.

Using the Phylochip, Hazen and his team determined that the dominant microbe in the oil plume is a new species, closely related to members of Oceanospirillales family, particularly Oleispirea antarctica and Oceaniserpentilla haliotis.

The scientists attribute the faster-than-expected rates of oil biodegradation in part to the nature of Gulf light crude, which contains a large volatile component that is more biodegradable.

The use of the COREXIT dispersant may have also sped up the biodegradation due to the small size of the oil particles and the low overall concentrations of oil in the plume.

Furthermore, frequent episodic oil leaks from natural seeps in the Gulf seabed may have led to adaptations over long periods of time by the deep-sea microbial community that accelerate hydrocarbon degradation rates.

One of the concerns raised about microbial degradation of the oil in such a deepwater plume is that the microbes would also be consuming large portions of oxygen, creating so-called "dead-zones" in the water column where life cannot be sustained.

However, the researchers found that oxygen saturation outside the plume was 67-percent, compared with 59 percent within the plume.

"The low concentrations of iron in seawater may have prevented oxygen concentrations dropping more precipitously from biodegradation demand on the petroleum, since many hydrocarbon-degrading enzymes have iron as a component," Hazen said.

"There's not enough iron to form more of these enzymes, which would degrade the carbon faster but also consume more oxygen."

The research was published online in the journal Science on August 26, 2010 in a report entitled "Deep-sea oil plume enriches Indigenous oil-degrading bacteria."   An abstract can be viewed at http://www.sciencemag.org/cgi/content/abstract/science.1195979.

The study was supported by the Energy Biosciences Institute, a partnership led by the University of California, Berkeley and the University of Illinois that is funded by a 10-year, $500 million grant from BP.  The U.S. Department of Energy and the University of Oklahoma Research Foundation also provided support.


Image 1: Microbes are degrading oil in the deepwater plume from the BP oil spill in the Gulf, a study by Berkeley Lab researchers has shown. (Image from Hoi-Ying Holman group)

Image 2: Analysis with Berkeley Lab's phyloChip revealed the dominant microbe in the dispersed Gulf of Mexico oil plume was a new species, closely related to members of Oceanospirillales family. (Image from Terry Hazen group)


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