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Winter 1997

Research Magazine > ARCHIVE > Spring 96 > Article

Soaking Up Some Heavy Metal
by Jennifer T. Daly
(UGA science writer Phil Williams contributed to this story)

All the signs were there. Dead fish washed ashore. Shellfish disappeared. Seagull hatchlings bore deformities.

But these warnings went unheeded, and by 1956, the people along the shores of Minamata Bay, Japan, began to suffer such symptoms as numbness, hearing loss and brain damage. What is now known as "Minamata Disease" finally was traced to mercury pollution from a nearby factory.

Forty years later, mercury pollution is still a global problem. Because as anyone who has broken an old-fashioned thermometer knows, even in its most solid form, mercury is extremely difficult to clean up.

That's why the tiny plants growing in Richard Meagher's laboratory are receiving increasing attention.

The University of Georgia genetics professor and his colleagues have altered a bacterial gene that, when inserted into the sprout-like arabidopsis plant, shows a significant ability to absorb toxic salts of mercury and convert the mercury to a comparatively harmless vapor.

"The results were just astounding -- far better than what we had expected," Meagher said.

Though it works in a petri dish, any real-world benefit depends on whether the gene, labeled merA, can be inserted successfully into larger, sturdier plants that live in mercury-polluted areas.

"Agricultural land in Florida, for example, is heavily contaminated with mercury from fungicides and bactericides used in citrus groves," Meagher said.

A fringe of transgenic plants -- those that have the foreign gene inserted -- could be planted around polluted areas to stop contaminated runoff from reaching wetlands and the food chain, Meagher said. "This technology could have a huge environmental impact on any site contaminated with heavy metals."

But as excited as he is by its potential, Meagher said he believes several years lie between the lab and real-world applications because of the inherent difficulty of inserting genes into a foreign host.

The merA gene was first studied many years ago by UGA microbiologist Anne Summers. It is common in the abundant soil-borne bacteria that thrive only in areas polluted by mercury and other heavy metals. In their natural state, the merA-containing bacteria detoxify mercury to a degree, but they do not provide large-scale uptake of the metal.

The first challenge for the UGA team was to see if the gene could even survive in a plant. One of Meagher's graduate students first inserted the gene in a petunia in 1989, but the plant failed to grow on mercury.

Last year under Meagher's direction, undergraduate student Nicole Stack altered the genetic sequence of merA, which differed only 9 percent from its original state. Then post-doctoral associate Dayton Wilde helped insert the new gene into arabidopsis -- chosen because the small plant, a relative of cabbage and radish, grows fast, produces plenty of seeds and has a small gene pool. Finally, graduate student Clayton Rugh followed the genetically engineered plant's ability to grow in and reduce the amount of mercury in the petri dish.

The researchers were surprised how well it worked. Without the merA gene, arabidopsis died or, in some cases, never grew beyond a few feeble sprouts in the mercury-rich petri dishes. The plants with the foreign gene flourished, and, in fact, now require mercury to grow. In addition, the seeds of these lab plants have inherited the merA gene.

But their success is tempered by the unknown.

"Different soil varieties and growing conditions may necessitate further adjustments in the gene's design," Meagher said. "Will this process prove as effective in the real world as it does in a petri dish? We don't know."

Post-doctoral research associate Stan Dudka currently is putting the genetically modified arabidopsis to the soil test. His research should reveal whether the plant converts as much mercury to vapor in soil as it does in a petri dish. And Rugh, under the direction of forestry Professor Scott Merkle, is now working to successfully insert the gene into yellow poplar trees.

But the project is not without criticism. Mercury vapor is not completely risk-free, and some environmentalists, Meagher said, have expressed concern about large fields of plants releasing mercury vapor.

"It's not a perfect solution," he said, "but releasing much less toxic forms of mercury into the air--where eventually it would deposit at naturally low concentrations -- makes more sense than leaving highly toxic mercury in areas that expose humans and wildlife to danger."

And it could prove to be a more viable, cost-effective alternative than current remedies like burying or incinerating contaminated soil, he said.

Meagher said he and his team are expanding their efforts to another gene, merB, which if combined with merA, should act on the most deadly form of mercury: methyl mercury, which is the form that entered the food chain through Minamata Bay.

Theoretically, the gene also could be altered to remove other heavy metals, such as copper and lead. And a recent experiment proved that the gene might have value beyond detoxifying pollutants. Arabidopsis plants with merA grew well in the lab on ionic gold.

"It's a fun prospect," Meagher said. "The plants could be burned off and the gold would remain."

But a paucity of funding for such projects, even for the already successful merA research, continues to be a problem, he said.

"In this area of research I have had 19 grants turned down in 14 years," Meagher said. In fact, he said, the merA research would have ended long ago if it were not for UGA biotechnology start-up funds and grants from the U.S. Environmental Protection Agency. The success of the research finally has brought in the project's first National Science Foundation grant.

"It's 10 to 20 years off, but I believe this research will lead to real solutions for heavy metal pollution," Meagher said. "There are no guarantees, but it looks good so far."

For more information, please go to http://www.genetics.uga.edu/faculty/bio-Meagher.html or e-mail meagher@arches.uga.edu


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