Fussy Microbe Holds Promise For Environmental Cleanup

In this week's issue of Science, researchers from MSU's Center for Microbial Ecology report the discovery of a microbe dredged from the bottom of the Hudson River that has an insatiable appetite to break down the environmental pollutant TCA.

"TCA was one of the remaining groundwater pollutants for which biodegradation had not been resolved," said James Tiedje, a University Distinguished Professor of microbiology and molecular genetics and of crop and soil sciences. "Till now, there wasn't good evidence there was a biodegradable solution."

That means the bacterium shows promise as the missing piece of the puzzle to clean up soil and groundwater that is contaminated by multiple chlorinated solvents. Microbes that munch other toxins have been isolated, but TCA-eating bugs have remained a mystery.

"For a while, people didn't think this bug existed," said postdoctoral student and co-author Baolin Sun. "Now we've solved it."

TCA – 1,1,1-Trichloroethane – is a common industrial solvent that's found in half of the U.S. Superfund sites. As a pollutant, it packs a double punch, contaminating groundwater as well as eroding the ozone layer when released into the atmosphere.

In the Science article "Microbial Dehalorespiration with 1,1,1-Trichloroethane," Tiedje's team identified TCA1, an anaerobic bacterium with a single-minded taste for TCA.

"This is the first bacterium that breathes the chlorinated solvent TCA," said MSU doctoral student Benjamin Griffin. "It breathes TCA, and the only way we know how to grow the bacteria is to feed it TCA."

The MSU group found TCA1 in the sediment of the upper Hudson River in New York. The bacterium also occurs naturally in Michigan's Kalamazoo River.

TCA1 handily chows on the toxin, converting it to chloroethane, a less toxic substance that can then be easily degraded by aerobic microbes in soil. The beauty of the newly discovered bacterium is that it does its work under water, preventing the toxin from escaping into the atmosphere and causing ozone depletion.

Finding TCA1 and understanding how to make it thrive is a first step in devising ways to put the bacterium to work cleaning up contaminated sites that until now were left with a piece of the puzzle unsolved.