By Sean Henahan, Access Excellence

Caption: Major Muncher, Thin-section electron micrograph of coccoid strain 195.

Researchers at Cornell University isolated the antibiotic-resistant anaerobic bacterium sewer sludge.  The investigators were pleased to find that coccoid Strain 195 perfectly reduces the toxic pollutants tetrachloroethene and trichloroethene (also known as PCE, or perc, and TCE, respectively) to nontoxic ethene gas. 

"Strain 195 uses tetrachloroethene much like we use oxygen," explains Cornell microbiologist Stephen  H. Zinder, describing the reduction process that leaves little more than ethene, also known as ethylene, the natural gas that causes fruit to ripen.

Chlorinated solvents are the basis for cleaners used to remove dirt and oils from clothes, engines, machines, and electronic parts. Until recently, the used solvents routinely were dumped into landfills, stored in leaky disposal tanks or spilled on the ground. Prior to the discovery of Strain 195, the best available  bioremediation organisms could only reduce tetrachloroethene to vinyl chloride. This had the effect of changing a suspected carcinogen into a known carcinogen.

Much research is still needed before Strain 195 can be unleashed on unsuspecting PERC sludge. The bacterium is difficult to grow by itself; requring chemical collaboration with other bacteria. The bacterium also does not make its own vitamin B-12, a vitamin necessary for its survival. The team is now ready, thanks to funding from the U.S. Air Force, to begin experimental bioremediation protocols aimed at cleaning up military airbases with subterranean pollution problems.

Among the potential bioremediation test sites are a former B-52 airbase in Plattsburgh, N.Y., where planners hope to replace Air Force operations with an eco-industrial park, and a still-functioning base in Fallon, Nev., where the U.S. Navy's "Top Gun" fighter pilots train.  Like many other airbases,the New York and Nevada facilities harbor concentrations of toxins, especially around pits where crash-and-rescue personnel dumped jet fuel for firefighting practice -- and threw in leftover chlorinated solvents "to get rid of them."

Tetrachloroethene, trichlorothene and other related chemicals are the the number-two ground water pollutant (after petroleum hydrocarbons). The researchers think Strain 195 and other microorganisms may already be hard at work at some pollution sites, a possibility they will investigate.

"As we piece together the family tree for these organisms, we can develop gene probes and ask: 'Who's here?  Which dechlorinators are working here?' And that will tell us whether some enhancement would be helpful or whether the problem will take care of itself," said James M. Gossett, the Cornell professor of civil and environmental engineering.

The research appeared in the June 6, 1997, issue of Science.