A bacterium called Desulfovibrio desulfuricans strain ND132 can transform elemental mercury into methylmercury, a human neurotoxin. |
A
newly sequenced bacterial genome from a team led by the Department of
Energy’s Oak Ridge National Laboratory could contain clues as to how
microorganisms produce a highly toxic form of mercury.
Methylmercury,
a potent human neurotoxin, appears in the environment when certain
naturally occurring bacteria transform inorganic mercury into its more
toxic cousin. Few bacterial species are capable of this conversion, and
exactly how the transformation takes place has been a matter of debate
for decades.
“What
is not known are the genes or the proteins that allow these bacteria to
mediate the transformation,” said ORNL’s Steven Brown, who led a
research team to sequence the genome of a bacterium in the Desulfovibrio
genus that is capable of methylating mercury.
The
new genome, sequenced at the California-based DOE Joint Genome
Institute (JGI) and published in the Journal of Bacteriology, lays the
foundation for future research to examine the little understood
mechanisms behind the production of methylmercury.
Desulfovibrio
desulfuricans strain ND132 is an organism that thrives in sediments and
soils without oxygen – the places in lakes, streams and wetlands where
mercury contamination is converted to methylmercury. It is
representative of a group of organisms that “breathe” sulfate instead of
oxygen and are largely responsible for mercury methylation in nature.
“This
is the first Desulfovibrio genome that will methylate mercury that’s
been published,” Brown said. “Now that we have this resource, we can
take a comparative approach and look at what is different between the
bacteria that can methylate mercury and those that are unable to.”
The
introduction of mercury into the environment primarily stems from its
use in industrial processes and from the burning of fossil fuels.
Although industry and regulators have worked to minimize the release of
mercury, there is a legacy of mercury pollution in aquatic environments
worldwide. Understanding the fundamental science behind the production
of methylmercury could eventually help mitigate and reduce the impacts
of mercury pollution.
“Mercury
is a global contaminant of concern,” Brown said. “We hope that some of
the lessons we learn from these studies will be applicable to many
sites. If we can identify the genes involved in mercury methylation, we
hope to go to the local environment and understand more about the
function and the ecology of the organisms and their gene products that
mediate this transformation.”
The
study was published as “Genome Sequence of the Mercury Methylating
Strain Desulfovibrio desulfuricans ND132.” Collaborators included
researchers from ORNL, the Smithsonian Environmental Research Center,
the University of Missouri and Lawrence Berkeley National Laboratory’s
JGI. The research was supported by DOE’s Office of Science. ORNL is
managed by UT-Battelle for the Department of Energy’s Office of Science.
