Dehalococcoides mccartyi BAV1

SEM images by the late Dr. Robert P. Apkarian and Jeanette Taylor, at the Integrated Microscopy & Microanalytical Facility (IM&MF), Department of Chemistry, Emory University, Atlanta, GA

Dehalococcoides sp. strain BAV1 performs reductive dechlorination and transforms chlorinated ethenes, including vinyl chloride, to innocuous products (i.e., ethene and inorganic chloride); has been successfully employed in bioremediation at chlorinated solvent sites.

Basic Facts of Dehalococcoides sp. strain BAV1, including why it is important and motivation behind sequencing:

(i) Dehalococcoides sp. strain BAV1 detoxifies chlorinated ethenes.   Widespread groundwater contamination with chlorinated solvents, particularly chlorinated ethenes, poses environmental and health concerns.   Many organisms dechlorinate tetrachloroethene (PCE) to trichloroethene (TCE) and cis -1,2-dichloroethene ( cis -DCE), and recent study demonstrated that trans -DCE can also be a major product of microbial PCE/TCE metabolism (3) .   All chlorinated ethenes are toxic, and only complete dechlorination results in detoxification.   Prior to isolation of strain BAV1, only two bacterial populations were described as capable of dechlorinating PCE to ethene; Dehalococcoides ethenogenes strain 195 uses PCE, TCE and cis -DCE as metabolic electron acceptors (15) , and Dehalococcoides sp. strain FL2 grows with TCE, cis -DCE, and trans -DCE (9) .   Unfortunately, neither of these two populations grow with VC and the final dechlorination step, VC to ethene, proved to be cometabolic and slow, resulting in VC formation (9, 14, 16-18) .   VC accumulation is particularly troublesome because VC is a human carcinogen.   Overcoming the DCE and VC stall is a major obstacle in bioremediation of chlorinated solvent sites.

Dehalococcoides sp. strain BAV1 was isolated from PCE-to-ethene-dechlorinating microcosms established with aquifer material collected at the contaminated Bachman Road site in Oscoda, Michigan (6-8, 13) .   Strain BAV1 grows using all DCE isomers and VC as electron acceptors and cometabolizes PCE and TCE, thus efficiently converting these toxic compounds to environmentally benign ethene and inorganic chloride (5, 7) .

Isolating strain BAV1 demonstrated the existence of organisms that efficiently detoxify chlorinated ethenes, including VC, to environmentally benign products (i.e., ethene and inorganic chloride), and represented a milestone for bioremediation applications at chlorinated solvent sites.   The genome sequence of strain BAV1 will provide information on the evolution of reductive dehalogenation and the environmentally relevant Dehalococcoides group.   The genome will serve as a blueprint for the design of molecular tools to assess and manipulate dechlorination activity at contaminated sites.

(ii) Dehalococcoides spp. dechlorinate a range of chlorinated pollutants including chlorinated benzenes and polychlorinated biphenyls (1, 2, 4, 10, 11, 16, 19) .   Chlorinated compounds are abundant environmental pollutants, and innovative, affordable and effective bioremediation approaches are needed.   Dehalococcoides sp. strain BAV1 is recognized for its ability to detoxify chlorinated ethenes; however, genome analysis is revealing the presence of numerous reductive dehalogenase genes.   Similar to what has been learned from the genomes of Dehalococcoides ethenogenes strain 195 (20) and Dehalococcoides sp. strain CBDB1 (12) , strain BAV1 appears to dechlorinate a broad range of chloroorganic compounds.   Comparative genome analysis combined with culture-based experimentation and expression analysis will denote the range of chloroorganic chemicals Dehalococcoides uses for growth and contribute to the fundamental understanding of the ecology and biology of this environmentally relevant bacterial group.


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