ITHACA, N.Y. -- "The born-to-dechlorinate bug" is what Cornell University researchers called Dehalococcoides ethenogenes Strain 195 when they found the bacterium obligingly detoxifying the pollutant PCE, or perchloroethylene (a chlorinated solvent used for dry cleaning), in sludge from an Ithaca, N.Y., sewage treatment plant. Their discovery led to two questions: Might cultures of the naturally occurring microorganism serve as bioremediation agents to clean up sites where solvents such as PCE and TCE (trichloroethylene) -- used to clean metal parts -- had been dumped or spilled? And what on earth had the bug been eating before synthetic chlorinated compounds were invented some 50 years ago?

Sequencing of the Strain 195 genome at the Institute for Genomic Research (TIGR), Rockville, Md., which is reported in the latest issue of the journal Science (Jan. 7, 2005), helps resolve the second question. An up-and-coming bioremediation industry, based on Strain 195, answers the first.

"Strain 195 has a relatively small genome, only about a third the size of E. coli's in base pairs, but it's a highly adaptable one with clusters of genes called mobile genetic elements," says Cornell professor of microbiology Stephen H. Zinder. He named and studied Strain 195 after James M. Gossett, Cornell professor of civil and environmental engineering, found the enterprising organism in sewage sludge.

"Just by picking up these mobile genetic elements from other bacteria, Dehalococcoides strains seem able to adapt and to take advantage of opportunities as they present themselves," Zinder notes.

The genomic analysis showed how various Dehalococcoides strains are able to make enzymes called reductive dehalogenases to dechlorinate chlorobenzenes, chloronapthalenes, polychlorinated biphenyls and dibenzodioxins -- by turning the genes on and off as the organism detects something appetizing. Since Strain 195 requires diverse nutrient
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Contact: Bill Steele
ws21@cornell.edu
607-255-7164
Cornell University News Service
6-Jan-2005

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