What triggers toxics fighter?


Researchers are a step closer to understanding a one-celled organism used to clean up industrial waste.

An international team of scientists announced today the sequencing of the genome for Dehalococcoides ethenogenes, a type of bacteria that gobbles up toxic waste.

Aimed at identifying what triggers the cleanup process, the project shows that the bacterium is a particularly efficient creature, feeding off hydrogen and chlorine for energy as it destroys toxics.

"It's been evolving itself so that it can take up these compounds and degrade them," said Rekha Seshadri, lead author and a researcher at The Institute for Genomic Research in Rockville. "It's because of its efficiency that we discovered it.

The study, published in today's issue of Science, was funded by the Department of Energy. Researchers from the Johns Hopkins University and the University of Maryland Biotechnology Institute contributed to the report.

The new genetic analysis showed that D. ethenogenes has 1,591 genes (humans by comparison, have 20,000 to 25,000).

Bacteria are the most abundant life form on Earth. The one-celled organisms exist almost everywhere and usually live off other organisms.

Like us, they also evolve -- and some are believed to be adjusting to toxic environments in beneficial ways. "There's been a theory that as humans have developed these pollutants ... that bacteria have evolved to degrade them, that there's this evolution going on," Seshadri said.

D. ethenogenes seems to fit that description. A free-living organism, it dies in the presence of oxygen and is hard to create in a lab. But in 1997, researchers plucked some from a New York sewage treatment plant and discovered that it was an effective weapon against two common industrial pollutants -- perchloroethylene (PCE) and trichloroethylene (TCE). The compounds were dumped for decades at about 50,000 industrial sites around the country.

"It's an extremely good bacterium because of its potential," said Kirsti Ritalahti, a bacteria researcher at Georgia Institute of Technology.

PCE and TCE are chemical byproducts of cleaners used by many industries, including dry cleaners and computer manufacturers, before federal mandates imposed strict disposal restrictions in the 1980s.

It was those compounds that caused injuries to neighbors in a community in Woburn, Mass., that prompted an environmental suit portrayed in the book and movie A Civil Action.

"It's illegal to dump anything like that anymore. It all has to be recycled or carted away," said Sam Fogel, a microbiologist and consultant whose firm uses D. ethenogenes to clean up groundwater at industrial sites.

Contractors have used bacteria for years to clean up water contaminated by arsenic, radioactive material, fuel oil and many of the solvents spilled at military bases, service stations and industrial sites.

Exxon used bacteria to help clean up the southeast coast of Alaska after the Exxon Valdez oil spill in 1989.

Researchers at the University of Illinois have found that injecting sulfate salts into groundwater promotes bacteria that remove arsenic, and the Department of Energy is studying whether a bacterium that shows potential as a fuel source can clean up radioactive material at a uranium waste storage facility in Colorado.

Fogel said understanding D. ethenogenes' genetic code could lead to a better understanding of how the organism evolved, how it survives and the genes that trigger its thirst for toxic compounds.

"They may be able to figure out the mechanism for it, how the whole process works," said Fogel.

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