ORNL-led team hails breakthrough in mercury research; could have global implications

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KNS photo/Michael Patrick
Liyuan Liang, right, leader of the ORNL’s mercury research program, and microbiologist Dwayne Elias talk about the discovery of genes associated with production of methylmercury in the environment.
An Oak Ridge-based research team has identified two genes in microorganisms that are responsible for an environmental process that converts mercury into its most toxic form — methylmercury.
The discovery is being hailed by scientists at Oak Ridge National Laboratory as a long-awaited breakthrough and a possible step toward minimizing the global health hazards of mercury in the environment.
The research results, which will be published in the journal Science, were embargoed until 2 p.m. today.

“We’ve known for 40 years that bacteria are what transforms mercury into methylmercury, but nobody’s been able to figure out how they do that — until now,” said Jeremy Smith, who holds a Governor’s Chair at the University of Tennessee and directs ORNL’s Center for Molecular Biophysics.
Researchers said multiple factors likely contribute to the creation of methylmercury, but they’ve now determined that a pair of genes — identified as hgcA and hgcB — are essential to that process. Those genes are reportedly found in many different bacteria, all of which may be capable of producing the toxic form of mercury under the right circumstances. Researchers say this new knowledge will let them explore how the processes work, develop methods to identify mercury-contaminated sites with vulnerable conditions, and perhaps come up with ways to stop the microbial bugs from doing their dastardly deeds.
Liyuan Liang, who heads the Department of Energy-funded mercury research program at ORNL, said the discovery was made a year ago, but it took months to validate those findings through a series of painstaking lab experiments in which the two genes were deactivated — individually and as a pair — and tested to see if they lost their ability to produce methylmercury. Additional tests were conducted in which those genes were then turned on again to confirm their function.
Liang said the results were exciting, important, and rewarding.
“I think we can begin to understand the mechanisms and begin to develop tools to detect these microorganisms in the environment and assess the amount of methylmercury production and — in the future — how you can minimize that,” she said.
The team working on the mercury project included ORNL scientists with multiple areas of expertise, as well as researchers from UT and the University of Missouri.
The eureka-type discovery, however, was credited to Jerry Parks, a computational chemist, and Alex Johs, a structural biologist, at Oak Ridge National Laboratory.
According to members of the team, Parks and Johs were able to identify the genes of consequence by studying chemical reactions at work in the environment and then applying that understanding to proteins potentially capable of carrying out that chemistry — with the presence of cobalt as a key. After working feverishly on a hypothesis for a few days, the scientists presented their findings to the broader group on Feb. 3, 2012.
“There was this initial burst of inspiration from Alex and Jerry,” Smith said, which was followed by experiments that ultimately proved them correct.
In order for microorganisms to break down mercury and create the methyl form, both of the genes have to be present and functioning, the researchers said.
Mercury is a toxin of international concern. The element is spread globally through industrial uses, including emissions from coal-burning energy plants, and natural processes such as volcanic eruptions. Methylmercury is a carcinogen and neurotoxin, and it is a special concern because it bioaccumulates in the food chain. Humans are at risk from eating fish and fowl with mercury-contaminated diets.
Dwayne Elias,a microbiologist at ORNL, said the discovery linking specific genes to the production of methylmercury will allow scientists to push the boundaries of knowledge in multiple directions. “This changes everything,” he said.
“We’d like to get to the point where we give people who are working in the field a tool where they can take a little creek water, a little lake water, put it in a mix that we would develop, and in a few seconds — or a few minutes — they would be able to say there’s a lot of mercury methylators here or there’s very little here,” Elias said.
“We’ve just made this discovery, so we’re still figuring out the best things to do first. One of the important things we think is important is nailing down just how these proteins work, and that’s where structural chemistry comes into play. Once we know how they work, then we can make informed decisions on how to stop them from working.”
ORNL is becoming a major center for mercury research, with what’s essentially a large field lab in its backyard.
The nearby Y-12 nuclear weapons plant used enormous quantities of mercury during the Cold War development of hydrogen bombs, and an estimated 2 million pounds was either lost or unaccounted for during the 1950s and ’60s. Tons of mercury entered East Fork Poplar Creek, which has been posted as a mercury hazard since 1982, and lab researchers have used the creek for some of their field studies.
Liang and Elias said the discovery of genetic links to production of methylmercury could be put to use in future cleanup operations at Y-12, where large quantities of mercury reside in the walls and basements of buildings. Pools of mercury also exist in the soils at Y-12 and in the groundwater underneath the site.

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About Frank Munger

Senior Writer Frank Munger covers the Dept. of Energy's Oak Ridge facilities and many related topics — nuclear weapons, nuclear waste and other things nuclear, environmental cleanup and science of all sorts. Atomic City Underground is, first and foremost, a news blog, but there's room for analysis, opinion and random thoughts that have no place else to go.