High-Tech Bacteria On Tap For Toxic Clean-Up DutyBy
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
Pathology Laboratory, Beltsville, Md., phone (301) 504-5736, fax (301) 504
Hollowell or Sisir Dutta, Howard University, Washington, D.C., phone (202)
806-6942, fax (202) 806-5832, firstname.lastname@example.org.