Gene-Altered Plant, Tree Can Suck Up Toxins

John Roach
for National Geographic News

October 15, 2007

Two types of genetically modified plants can remove toxic compounds from the environment, according to research by a pair of independent groups.

One group developed Arabidopsis plants—small plants related to cabbage and mustard—that can clean up soil contaminated with cyclonite, or RDX. The widely used explosive is highly toxic and carcinogenic.

The other team modified a poplar tree to soak up a host of cancer-causing compounds from soil, groundwater, and air.

The contaminants are then broken down into harmless compounds in a process called phytoremediation. (Related news: "Plants Perform 'Green Clean' of Toxic Sites" [September 24, 2004].)

"It is our hope that by developing trees that can remove carcinogens from the water and air in a fast and economical way, people will be more likely to use [the land] than abandon the property as too expensive to clean up," Sharon Doty, of the University of Washington, said in an email.

Doty is the lead author of a paper on the modified poplar tree that appears this week in the journal Proceedings of the National Academy of Sciences.

"There is more research left to be done before we reach that stage, but that is the ultimate goal."

But outside experts cautioned that the risks of using genetically engineered plants are unknown and require rigorous testing.

"I think we're playing to some extent a game of roulette here," said Doug Gurian-Sherman with the Union of Concerned Scientists in Washington, D.C.

He noted that both Arabidopsis and poplars spread naturally in the wild, which heightens the risk of an engineered gene spreading unchecked.

"If they do [escape and] cause problems," he said, "we're pretty much going to be stuck with them."

Explosives Breakdown

Neil Bruce at the University of York in the U.K. co-authored a paper on the explosive-slurping Arabidopsis plant, which also appears this week in PNAS.

Several years ago the biologist and colleagues found a soil microorganism that had adapted to use the nitrogen found in RDX to grow.

This microbe has since been found at RDX-contaminated sites around the world.

"But whilst you can find these microorganisms there, they clearly aren't breaking down the explosive fast enough before it migrates through the soil and contaminates groundwater," Bruce said.

Plants are well known for soaking up certain chemicals from soil, air, and groundwater and breaking them down into harmless components, he said. But no known plant naturally breaks down RDX.

So Bruce and colleagues combined the enzyme system from the soil microbes with Arabidopsis, a model plant for scientific studies because its genetic changes are easily observed (get a genetics overview).

Their first successful attempt was published in the January 2006 issue of the journal Nature Biotechnology. The new research published this week in PNAS documents the plants' superior performance.

"We've managed to identify the complete systems that allow this enzyme to work, and we've got both components of this enzyme system successfully expressed and working in Arabidopsis," Bruce said.

His team is now collaborating with researchers at the University of Washington in Seattle to develop grasses and trees more suited to removing RDX from contaminated soils at military bases around the world.

Contaminant Cleaning

Stuart Strand, a research professor in the College of Forest Resources at the University of Washington, leads the collaboration with Bruce's team and is also a co-author of the paper on transgenic poplar trees.

That study used a similar technique to enhance the ability of poplar trees to remove a host of carcinogens from the environment.

In this case, the team inserted a gene that produces a contaminant-cleaning enzyme found in rabbit livers into the poplar trees.

Although poplars already naturally remove contaminants from the environment, the rabbit liver enzyme speeds up the process.

For example, the altered poplars removed trichloroethylene—a heavily used industrial degreaser—53 times faster than nonaltered trees, lead study author Doty noted.

The trees also more quickly removed carcinogens such as chloroform and vinyl chloride from the ground and benzene from the air.

And while control plants removed none of the industrial solvent trichloroethylene from the air, the altered trees removed 79 percent of the chemical during a week-long experiment.

Doty added that poplars grow for several years before flowering, and fallen branches do not take root in soil. As such, the trees could be harvested before their seeds germinate and spread their genes.

But Jane Rissler, of the Union of Concerned Scientists, cautioned that promises of safe bioremediation techniques seldom come to fruition.

"There have been so many promises in the past 20 years and so few products," she said, "and phytoremediation is another promise that hasn't been met."

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