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Spring 2000

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Pollution-Eating Plants
by Catherine Gianaro

Time was, pollution-eating plants grew only in science fiction.

Today they're science fact. UGA genetics professor Richard Meagher and his colleagues have genetically altered trees and other plants to absorb toxic mercury from the soil, convert it to a comparatively harmless gas and release it in the air.

Meagher first modified the merA gene - borrowed from mercury-resistant bacteria - and inserted it in the diminutive arabidopsis plant (Research Reporter, Winter/Spring 1996). After initial success, the scientists expanded the research to include tobacco, cannola and rice plants, as well as yellow poplar trees, most of which tested well in the greenhouse.

The fast-growing yellow poplar, which has large leaves that provide plenty of surface area to release the converted gas, will be tested on contaminated field sites over the next few years. In preliminary test results, recently published in Nature Biotechnology, the genetically altered trees showed a 10-fold increase over control trees in their ability to absorb toxic mercury ions and convert them to a vapor.

The mercury-consuming bacteria can detoxify metals, but not nearly effectively enough to help clean up the estimated $200 billion worth of heavy metal pollution in the United States. That's why scientists want to transfer the bacteria's metal-eating traits into plants.

"Trying to engineer plants to hyper-accumulate metals is a type of harvesting process," Meagher said. "There's really no way to get rid of a metal, but you can convert it into a vapor, which is a thousand times less toxic and won't contaminate the food chain."

Meagher already had shown that his genetically engineered plants detoxify ionic mercury to a harmless gas. The challenge now is to clean up methyl mercury pollution - the type created in various industries, from farm pesticides to pulp and paper mill spills.

The EPA recently reported that mercury is the No. 1 metal pollutant due to the vast amount of contaminated sites and its extreme toxicity. It contaminates tens of thousands of sites in the United States, Meagher said.

"There's not a state that doesn't have a lot of mercury pollution," he said. "Agricultural land in Florida, for example, is heavily contaminated with mercury from fungicides and bactericides used in citrus groves."

When methyl mercury enters the food chain, its effects on people and animals can be serious, causing neurological illnesses, birth defects - even death.

To act on the deadly methyl mercury, Meagher's team and collaborators in the forestry and microbiology departments turned their attention to another gene, merB. UGA scientists successfully have inserted the merB gene in arabidopsis plants and yellow poplar trees, and now are trying it with rice and tobacco.

Transgenic trees or other plants - those that have a foreign gene inserted - could be planted in a fringe 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 the project is not without criticism. Mercury vapor is not risk-free, Meagher said, and some environmentalists 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 where it is biomagnified and exposes 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.

The research, mostly funded by the U.S. Department of Energy Environmental Management Science Program, suggests the gene also could be altered to remove other contaminants, such as copper, lead, arsenic and cadmium.

"This research will lead to real solutions for heavy metal pollution," Meagher said. "While the European community is still debating whether or not to use genetically altered plants, I'm hoping to clean up the whole country."

For more information, access http://www.genetics.uga.edu/RBMSite/
or e-mail meagher@arches.uga.edu.

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