I find fascinating, and many readers also seem to, the role of oil-eating
bacteria in the Gulf of Mexico disaster. Fascinating for any number of reasons:
not only is the role of such microbes in the normal ecosystem remarkable, but
their appetite for hydrocarbons contributes significantly to the removal of
spilt oil on the surface and at depth – and equally remarkable is, in reality,
how little we know about them. I first described alcanivorax
borkumensis back at the beginning of June, with follow-ups a couple
of weeks later and then in
July. Now, in the interests of updating this ever-evolving theme – and
finding the science in the “debate” about what has happened to the oil – here’s
some extremely interesting news. Workers at the Lawrence Berkeley National
Laboratory have just described their discovery “that microbial activity,
spearheaded by a new and unclassified species, degrades oil much faster
than anticipated.” The italics are mine.
Here's the Berkeley
Lab press release – a noteworthy and, to me at least, astonishing detail
is the device used: “Sample analysis was boosted by the use of the latest
edition of the award-winning Berkeley Lab PhyloChip – a unique credit card-sized
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.”
Study shows deepwater oil plume in Gulf degraded by
microbes
Aug 24 2010
In the aftermath of the explosion of BP’s Deepwater Horizon drilling rig in
the Gulf of Mexico, a dispersed oil plume was formed at a depth between 3,600
and 4,000 feet and extending some 10 miles out from the wellhead. An intensive
study by scientists with the Lawrence Berkeley National Laboratory (Berkeley
Lab) found that microbial activity, spearheaded by a new and unclassified
species, degrades oil much faster than anticipated. This degradation appears to
take 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,” says Terry Hazen, a microbial ecologist with Berkeley Lab’s Earth
Sciences Division and principal investigator with the Energy Biosciences
Institute, who led this study. “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 in the Gulf of Mexico from BP’s deepwater well
was the deepest and one of the largest oil leaks in history. The extreme depths
in the water column and the magnitude of this event posed a great many
questions. In addition, to prevent large amounts of the highly flammable Gulf
light crude from reaching the surface, BP deployed an unprecedented quantity of
the commercial oil dispersant COREXIT 9500 at the wellhead, creating a plume of
micron-sized petroleum particles. Although the environmental effects of COREXIT
have been studied in surface water applications for more than a decade, its
potential impact and effectiveness in the deep waters of the Gulf marine
ecosystem were unknown.
Analysis by Hazen and his colleagues of microbial genes in the dispersed oil
plume revealed a variety of hydrocarbon-degraders, some of which were strongly
correlated with the concentration changes of various oil contaminants. Analysis
of changes in the oil composition as the plume extended from the wellhead
pointed to faster than expected biodegradation rates with the half-life of
alkanes ranging from 1.2 to 6.1 days.
“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 says. “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 on May 25, 2010. At that time, the
deep reaches of the Gulf of Mexico were a relatively unexplored microbial
habitat, where temperatures hover around 5 degrees Celsius, the pressure is
enormous, and 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 says. “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.”
Hazen, who has studied numerous oil-spill sites in the past, is the leader of
the Ecology Department and Center for Environmental Biotechnology at Berkeley
Lab’s Earth Sciences Division. He conducted this research under an existing
grant he holds with the Energy Biosciences Institute (EBI) to study microbial
enhanced hydrocarbon recovery. EBI is a partnership led by the University of
California (UC) Berkeley and including Berkeley Lab and the University of
Illinois that is funded by a $500 million, 10-year grant from BP.
Results in the Science paper are based on the analysis of more than
200 samples collected from 17 deepwater sites between May 25 and June 2, 2010.
Sample analysis was boosted by the use of the latest edition of the
award-winning Berkeley Lab PhyloChip – a unique credit card-sized 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. Use
of the Phylochip enabled Hazen and his colleagues to determine 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.
Hazen and his colleagues attribute the faster than expected rates of oil
biodegradation at the 5 degrees Celsius temperature 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 accelerated
biodegradation because of the small size of the oil particles and the low
overall concentrations of oil in the plume. In addition, 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 speed up
hydrocarbon degradation rates.
One of the concerns raised about microbial degradation of the oil in a
deepwater plume is that the microbes would also be consuming large portions of
oxygen in the plume, creating so-called “dead-zones” in the water column where
life cannot be sustained. In their study, the Berkeley Lab researchers found
that oxygen saturation outside the plume was 67-percent while within the plume
it was 59-percent.
“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 says. “There’s not enough iron to form more of these enzymes, which would
degrade the carbon faster but also consume more oxygen.”
[Image at the head of this post from the press release and the Terry Hazen
group. The results of this research were reported in the journal
Science (August 26, 2010 on-line) in a paper titled “Deep-sea oil plume
enriches indigenous oil-degrading bacteria.” Co-authoring the paper with Hazen
were Eric Dubinsky, Todd DeSantis, Gary Andersen, Yvette Piceno, Navjeet Singh,
Janet Jansson, Alexander Probst, Sharon Borglin, Julian Fortney, William
Stringfellow, Markus Bill, Mark Conrad, Lauren Tom, Krystle Chavarria, Thana
Alusi, Regina Lamendella, Dominique Joyner, Chelsea Spier, Jacob Baelum, Manfred
Auer, Marcin Zemla, Romy Chakraborty, Eric Sonnenthal, Patrik D’haeseleer,
Hoi-Ying Holman, Shariff Osman, Zhenmei Lu, Joy Van Nostrand, Ye Deng, Jizhong
Zhou and Olivia Mason.]