Study Reveals Microbes Dine on Thousands of Compounds in Oil


September 30, 2008

Thousands of feet below the bottom of the sea, off the shores of Santa
Barbara, CA, single-celled organisms are busy feasting on oil.

Until now, nobody knew how many oily compounds were being devoured by
the microscopic creatures, but new research led by David Valentine of
University of California at Santa Barbara (UCSB) and Chris Reddy of
Woods Hole Oceanographic Institution (WHOI) in Massachusetts has shed
new light on just how extensive their diet can be.

In a report published in the Oct. 1 edition of the journal Environmental Science & Technology,
researchers — Valentine, Reddy, lead author George Wardlaw, a graduate
student in the Marine Science program at UCSB, and three other
co-authors from Swiss Federal Institute of Technology and WHOI — detail
how the microbes are dining on thousands of compounds that make up the
oil seeping from the sea floor.

“It takes a special organism to live half a mile deep in the Earth and
eat oil for a living,” said Valentine, an associate professor of earth
science at UCSB. “There’s this incredibly complex diet for organisms
down there eating the oil.”

And, the researchers found, there may be one other byproduct being
produced by all of this munching on oil — natural gas. “They’re eating
the oil, and probably making natural gas out of it,” said Valentine.
“It’s actually a whole consortium of organisms — some that are eating
the oil and producing intermediate products, and then those
intermediate products are converted by another group to natural gas.”

Reddy, a marine chemist at WHOI, said the research provides important
new clues in the study of petroleum. “The biggest surprise was that
microbes living without oxygen could eat so many compounds that compose
crude oil,” Reddy said. “Prior to this study, only a handful of
compounds were shown, mostly in laboratory studies, to be degraded
anaerobically. This is a major leap forward in understanding petroleum
geochemistry and microbiology.”

The diet of the single-cell microbes is far more diverse than
previously thought, Valentine said. “They ate around 1,000 of the 1,500
compounds we could trace, and presumably are eating many more,” he said.

Research for this project began several years ago when Valentine
brought Reddy out to the natural hydrocarbon seep field right off the
California coast. Approximately 100 barrels of oil ooze out of the sea
floor there each day and bubble up 15 meters (45 ft) to the sea
surface. When the oil reaches the sea surface it is chemically changed
by evaporation and sunlight, the action of the water, and bacterial
activity.

“I was blown away by what I saw,” said Reddy, who has undertaken a
number of long-term studies on the impact of oil spills on the
environment. “Normally I arrive at an oil spill a day or two after it
has happened, and the most toxic, short-lived compounds have already
disappeared. I knew right away this site provided an important window
into the fate of oil in the environment, by providing the opportunity
to simultaneously sample oil from its sub-seafloor source to the sea
floor and up to the surface. It’s a really powerful snapshot.”

Natural seeps contribute nearly half of the oil entering the coastal
ocean. However, environmental fate studies generally monitor fewer than
five percent of these petroleum compounds. Using a new technique
devised by Reddy, the scientists were able to pick apart the
differences in the makeup of the oil along its migration route to the
surface through faults from deep below the sea floor. The microbes
prefer the lighter compounds of oil — the gasoline part of the black
goo. They tend to leave behind the heavily weathered residue, which is
what makes its way to the surface and, sometimes, to the beaches in the
form of tar.

“There always seems to be a residue,” Valentine said. “If you think of
oil as a buffet for microbes, there’s a point where they (bacteria) hit
a wall. There seems to be stages in which they eat. There’s the easy
stuff — the steak. And then they work their way to the vegetables, and
then garnish, and then they stop eating after awhile. It just depends
on how hungry they are and what’s fed to them.”

The samples were sent to Reddy’s lab in Woods Hole to be analyzed using
a diagnostic technology called a comprehensive two-dimensional gas
chromatography (GCxGC). Typically, chromatography involves heating up a
sample and putting it into a column – a wrapped coil tube a little
thicker than a strand of hair and approximately 60 meters long.
Compounds are then separated based on their boiling points, which works
well with light crude oil, Valentine said. But with the two-dimensional
test, the compounds are cooled to stop their motion for about 10
seconds, and a flash pulse of hot air releases them into a second
column, where the compounds travel at different speeds, allowing the
researchers to differentiate the many thousands of compounds.

“This new technology was actually too good at its job,” Reddy said. “It
was able to separate and help identify significantly more compounds in
the oil samples than traditional analytical techniques. The result was
that we were handcuffed with too much data afforded by the GCxGC.
However, we overcame this hurdle by using new algorithms to help us
interpret the data, which in turn led us to these milestone
discoveries.”

The next steps in their research are already under way, according to
Valentine. They are following the oil diet in controlled laboratory
conditions, and tracking the fate of the oil once it forms a slick at
the sea surface.

“When you fly out of the Santa Barbara Airport, you can look down and
see these massive slicks,” Valentine said. “You can follow them for
about 20 miles. A lot of the oil comes up on the beaches, but then what
happens to it after that? Certainly the microorganisms continue to act
on it. Evaporation occurs, but most of it can’t evaporate. Some of it
breaks down from sunlight. So where does the rest of it end up? We want
to know how far the organisms will go in eating the oil and what
happens to the residual tar. It doesn’t all stick to our feet and there
must be a lot of it out there somewhere.”

“The more biodegraded oil is, the ‘heavier’ it is and the less value it
has,” Reddy added. “Our understanding of what these microbes eat is
giving us a better grasp of the link between bacterial activity and the
quality of oil.”

This work was funded by grants from the U.S. National Science
Foundation, the U.S. Minerals Management Service, the California Toxic
Substance Research and Training Program, the U.S. Department of Energy,
and the Seaver Institute.

The Woods Hole Oceanographic Institution is a private, independent
organization in Falmouth, Mass., dedicated to marine research,
engineering, and higher education. Established in 1930 on a
recommendation from the National Academy of Sciences, its primary
mission is to understand the oceans and their interaction with the
Earth as a whole, and to communicate a basic understanding of the
oceans’ role in the changing global environment.