A newly sequenced bacterial¹ genome from a team led by the Department of Energy's Oak Ridge² National Laboratory could contain clues as to how microorganisms produce a highly toxic³ form of mercury（水银） . Methylmercury（甲基水银） , a potent⁴ human neurotoxin, appears in the environment when certain naturally occurring bacteria transform inorganic⁵ mercury into its more toxic cousin. Few bacterial species are capable of this conversion⁶, and exactly how the transformation⁷ takes place has been a matter of debate for decades.

"What is not known are the genes⁸ or the proteins that allow these bacteria to mediate¹⁰ the transformation," said ORNL's Steven Brown, who led a research team to sequence the genome of a bacterium¹¹ in the Desulfovibrio genus that is capable of methylating mercury.

The new genome, sequenced at the California-based DOE Joint¹² Genome Institute (JGI) and published in the Journal of Bacteriology, lays the foundation for future research to examine the little understood mechanisms¹³ behind the production of methylmercury.

Desulfovibrio（脱磷弧菌属） desulfuricans strain ND132 is an organism that thrives in sediments¹⁴ 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 legacy¹⁵ of mercury pollution in aquatic¹⁶ environments worldwide. Understanding the fundamental science behind the production of methylmercury could eventually help mitigate¹⁷ 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（可适用的） 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 gene⁹ products that mediate this transformation."