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Bacteria May Be Star Player in Toxic Cleanup

Anna Brendle
for National Geographic News
November 4, 2002
 
Scientists have discovered a strain of bacteria at the bottom of New York's Hudson River that might prove useful as an agent for cleaning up a common pollutant.

The microbe "breathes" a synthetic chemical known as TCA (1,1,1-trichloroethane), transforming it into a cleaner substance.

TCA is used as a solvent in many common products such as glue, paint, industrial degreasers, and aerosol sprays. It can also be created in landfills and hazardous waste sites when substances decompose and their chemical components interact.


The newly discovered bacteria remove chlorines from TCA to make chloroethane, a less toxic substance that can be more easily degraded by aerobic microbes in the soil, according to the researchers, who are based at Michigan State University's Center for Microbial Ecology.

Baolin Sun was the main author of a paper on the findings published in last week's issue of the journal Science. He and his colleagues, principal investigator James Tiedje and doctoral student Ben Griffin, named the anaerobic (oxygen-lacking) bacterium TCA1.

The bacterium "uses TCA in the same manner that people use oxygen," said Griffin. "This is the first [known] bacterium that breathes the chlorinated solvent TCA. It breathes TCA, and the only way we know how to grow the bacteria is to feed them TCA."

Common Pollutant

TCA is among the pollutants found at more than half of the so-called Superfund sites designated as priority areas for chemical cleanup by the U.S. Environmental Protection Agency (EPA).

TCA often leeches into groundwater and soil, contaminating supplies of drinking water. As TCA evaporates, it breaks down into chemicals that are released into the atmosphere, destroying Earth's protective ozone layer.

Federal government agencies such as the Agency for Toxic Substances and Disease Registry (ATSDR) and the EPA regulate TCA levels in groundwater and in the atmosphere. The manufacture of TCA has been banned in the United States since 1996, but the substance still exists in some industrial products.

Sun said the TCA-degrading bacteria may provide "a good opportunity to clean TCA from drinking water before it's released into the atmosphere."

The researchers initially discovered the bacterium in sediment dredged from the bottom of the upper Hudson River in New York, a Superfund site. Later they also found it growing naturally in Michigan's Kalamazoo River.

Boost for Bioremediation?

In the lab, the bacterium thrived as long as the researchers kept feeding it TCA. "We have not recreated the bacterium in the lab but enriched its activity and isolated a pure culture from the sediment source," said Sun.

TCA1 is "a naturally occurring bug—it's like we captured a wild animal and brought it into a zoo," Griffin added.

The researchers are now conducting physiological studies of the bacterium.

They hope it will prove useful in the growing field of bioremediation, the process of using microbes to clean up harmful chemicals from the environment.

Tiedje said the bacterium "is ready to be used in a field test. We have, with our environmental engineering team members, implemented other field remediation tests and feel we can apply the same technologies for this microbe."

It is not yet clear whether TCA1 is a microbe that has adapted locally as a result of the pollutants in the Hudson and Kalamazoo Rivers or occurs independently of pollutants.

"At this stage, we don't know," said Tiedje. "But we do know that the Hudson River has been our best site to find dechlorinating microbes, which may mean that there has been some natural adaptation."

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