High-Tech Bacteria On Tap For Toxic Clean-Up Duty

A new tool for decontaminating toxic soils could come from a high-tech "cousin" of natural bacteria that live on plant roots. Scientists genetically altered the soil microbe Rhizobium meliloti to make enzymes that degrade compounds called hydrocarbons. The chemicals are used in many products, but become contaminants once they escape into the environment.

The Rhizobium work is a cooperative project involving David Kuykendall of USDA's Agricultural Research Service, and Howard University's Sisir Dutta, Gail Hollowell and Li-Hua Hou. Their partners include colleagues at the National Institutes of Health and U.S. Army Corps of Engineers, which is funding the project.

The Army Corps is seeking inexpensive methods of cleaning soils at military bases or other areas without inflicting further environmental harm. Conventional techniques, like excavating and chemically treating soil, are costly and sometimes impractical.

According to the Environmental Protection Agency, the U.S. generates several hundred million tons of hazardous waste annually, with chemical manufacturers, petroleum refineries, and electroplating companies leading the way.

Recruiting the Rhizobium bacteria to do the dirty work of clean-up is appealing because it would take place on-site in an approach called in-situ bioremediation. The team's research began with Kuykendall's key insights into Rhizobium genetics and ecology. In nature, the bacteria live on roots of legumes like alfalfa, supplying the plants with nitrogen for growth. R. meliloti RP4:TOL, the genetically altered species, performs one extra duty. By secreting enzymes into soil, it can degrade hydrocarbons like toluene, which is used in fuels, solvents and other products.

When scientists added meta-toluate, a salt form of toluene, to a liquid culture of R. meliloti RP4:TOL, the altered bacteria completely degraded the compound into benign carboxylic acids. Greenhouse studies with alfalfa--the microbe's natural host--showed at least partial meta-toluate degradation at soil concentrations of 136 parts per million, a fairly toxic level.

Scientific contact: David Kuykendall, USDA-ARS Molecular Plant Pathology Laboratory, Beltsville, Md., phone (301) 504-5736, fax (301) 504 5449, dkuykend@asrr.arsusda.gov. Gail Hollowell or Sisir Dutta, Howard University, Washington, D.C., phone (202) 806-6942, fax (202) 806-5832, sdutta@fac.howard.edu.