Modified Tobacco Plant Removes TNT From Soil

Bijal P. Trivedi
National Geographic Today
December 7, 2001
Researchers have created a tobacco plant that can detoxify soil
contaminated with the military explosive trinitrotoluene (TNT). The
plant sucks TNT out of the soil and transforms it into another compound
that remains trapped within the plant.

The work is part of a
broader effort to engineer plants for cleaning up a variety of toxic
pollutants—a process called phytoremediation.

TNT and waste products from its production are highly toxic to plants and animals, and are known to cause anemia, liver damage, and cancer in humans. Yet large areas of land around the world are contaminated with the substances. Incineration is now the only way of decontaminating this soil, but the process is costly and generates unusable ash and possibly toxic fumes.

Researchers in the United Kingdom genetically modified tobacco plants to carry a gene from a soil-dwelling bacterium, Enterobacter cloacae. The bacterial gene produces an enzyme that transforms molecules of TNT into another less harmful compound that becomes "locked" in the plants.

The research, led by Neil Bruce of the University of Cambridge, is published in the December issue of the journal Nature Biotechnology.

To find a bacterium harboring such a gene, Bruce and his colleagues took soil samples from sites that were heavily contaminated with TNT. Bacteria are clever scavengers and evolve biological strategies for extracting carbon and nitrogen from various compounds.

"Bacteria have phenomenal capacity for evolution," said co-author Susan Rosser, also of the University of Cambridge, "and we knew that some bacteria living in these areas would have evolved to use TNT as a source of nitrogen."

Rosser and her colleagues inserted the appropriate gene into tobacco plants and found that the plants thrived in the presence of TNT. In unmodified tobacco plants, the development of roots and shoots was severely stunted.

"Eventually we would like to put this gene into poplar trees, which have an extensive root system which can reach down into the water table in some areas," said Rosser.

But applying the technology to contaminated sites could be "an uphill battle," according to Richard Meagher of the University of Georgia, who wrote an accompanying commentary.

"In the United States and Europe, government funding to basic research in phytoremediation is still pegged at only several million dollars a year, in contrast to the billions spent annually on Superfund site management and physical remediation methods," writes Meagher.

There is definitely not enough money for phytoremediation, especially when it comes to organic contaminants, such as dry-cleaning solvents and petroleum products, said Kathy Banks, director of the U.S. Environmental Protection Agency's Midwest Hazardous Substance Research Center at Purdue University in West Lafayette, Indiana. The Purdue center focuses on the use of indigenous species for remediation.

Rosser sees other hurdles as well. "There has been a huge public backlash against the introduction of genetically modified organisms," she said. "We hope that this work will convince people of the beneficial use of this technology."

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