Tobacco Takes Spark Out of TNT

Armed with a bacterial enzyme, tobacco can break down toxic explosives that contaminate the grounds at many ammunition factories, scientists report in the May issue of Nature Biotechnology. If the plant succeeds in field trials, experts say variants might be sicced on solvents and other organic pollutants.

According to the Environmental Protection Agency, the United States has 22 Superfund sites laced with explosive wastes, such as nitroglycerin or TNT. Patches of soil there contain enough TNT to detonate when exposed to flame or struck by an earthquake. The most widespread contaminant, TNT poses a more insidious threat to humans and wildlife, too: It can cause liver damage and cancer. The current approach for cleanup crews is to dig up and incinerate the tainted soil.

A few years ago, a team led by biotechnologist Neil Bruce of the University of Cambridge in the United Kingdom came across the makings of a gentler technique. While sieving through toxic soil, the researchers encountered a bacterium, Enterobacter cloacae, that thrives on the toxicants. The team isolated the responsible enzyme and found that it could degrade a variety of explosives, not just TNT.

Because it's hard to monitor bacteria dispersed on a field, the researchers transferred the TNT-cracking enzyme into tobacco plants. The seeds, they found, germinated in growth medium spiked with TNT or nitroglycerin, an environment that kills normal seeds. The altered seeds survived by absorbing the toxicants and breaking them down into nontoxic substances. Bruce says this represents a breakthrough, as plants cleaning up other kinds of waste "were simply accumulating the toxic substances."

In the young field of using plants to clean up toxic substances, the latest work is "the most revolutionary thing so far," says Brian Hooker, a biochemical engineer at Pacific Northwest National Laboratory in Richland, Washington. The technique of harnessing plants with bacterial enzymes is by no means limited to disposing of explosives, Hooker notes. "It can be expanded to anything for which an enzymatic degradation pathway is known."