In the results of a new study, scientists explain how they used DNA to identify microbes present in the Gulf of Mexico following the Deepwater Horizon oil spill – and the particular microbes responsible for consuming natural gas immediately after the spill.
temperature played a key role in the way bacteria reacted to the spill, the
of the National Academy of Sciences (PNAS) published the results in a recent
Valentine and Molly Redmond, geochemists at the University of California
at Santa Barbara (UCSB) conducted the study. The National Science Foundation
(NSF) and the Department of Energy supported it.
Deepwater Horizon oil spill was unique, according to Valentine and Redmond,
because it happened at such great depth and contained so much natural gas –
predominantly methane, ethane and propane.
factors influenced the way bacteria responded to the spill.
studies, Valentine, Redmond and colleagues showed that ethane and propane were
the major hydrocarbon compounds consumed in June 2010, two months after the
September 2010, the researchers discovered that these gases and all the methane
had been consumed.
In May and
June of 2010, the scientists found that bacterial communities in the submerged
plume were dominated by just a few types – Oceanospirillales, Colwellia and
Cycloclasticus – and were very different from control samples without large
concentrations of oil or gas.
bacteria also were very different from the microbial communities in surface oil
slicks collected at the same time.
much warmer at the surface than in the deep water – around 80 degrees F vs. 40
degrees F, which is pretty close to the temperature in your refrigerator,"
says Redmond, the PNAS paper's lead author.
was very little natural gas in the surface samples, suggesting that both
temperature and natural gas could be important in determining which bacteria
bloomed after the spill," she says.
bacteria she and Valentine saw in the deep-water samples in May and June were
related to types of psychrophilic, or cold-loving bacteria.
bacteria grow more slowly at cooler temperatures – that's why we keep our food
in the refrigerator," says Redmond. "But psychrophilic bacteria actually
grow faster at cold temperatures than they would at room temperature."
additional evidence of the importance of temperature, the scientists added oil
to water from the Gulf, and incubated it at 40 degrees F and at room
temperature (about 70 degrees F). They looked at which bacteria grew at the different
In the 40
degrees F samples, Colwellia were most abundant, but were only found in low
numbers in the room temperature samples, suggesting that the bacteria have an
advantage in cold water.
figure out which bacteria were consuming methane, ethane, and propane, we used
a technique called stable isotope probing, in which we incubated fresh seawater
samples from the Gulf with isotopically labeled methane, ethane or
bacteria that grew as they consumed the methane, ethane or propane converted
the labeled gases into biomass, including their DNA. By sequencing the DNA, the
scientists were able to identify the bacteria.
bacteria that consumed the ethane and propane were the same Colwellia in the
samples from May and June, when ethane and propane consumption rates were high.
They were abundant when the researchers incubated oil at 40 degrees F, but not
at room temperature.
suggests, say Valentine and Redmond, that the Colwellia grow well at low
temperatures, and can consume ethane and propane.
ability of oil-eating bacteria to grow with natural gas as their 'foodstuff' is
important," says Valentine, "because these bacteria may have reached
high numbers by eating the more-abundant gas, then turned their attention to
other components of the oil.
uncovered some of the relationships between hydrocarbons released from
Deepwater Horizon and the bacteria that responded," he notes.
questions remain about how the bacteria interacted with one another, and how
this affected the fate of the oil.
work continues to remind us that the ocean, its microbes, and petroleum
hydrocarbons share an ecological history that extends far into the geological
past," says Don Rice, director of NSF's chemical oceanography program,
which funded the research.
ability to respond to marine oil spills is enormously advanced by this kind of