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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.

References:

1. Adrian, L., U. Szewzyk, J. Wecke, and H. Görisch. 2000. Bacterial dehalorespiration with chlorinated benzenes. Nature 408: 580-583.
2. Cupples, A. M., A. M. Spormann, and P. L. McCarty. 2003. Growth of a Dehalococcoides -like microorganism on vinyl chloride and cis -dichloroethene as electron acceptors as determined by competitive PCR. Appl. Environ. Microbiol. 69: 953-959.
3. Griffin, B. M., J. M. Tiedje, and F. E. Löffler. 2004. Anaerobic microbial reductive dechlorination of tetrachloroethene (PCE) to predominately trans -1,2 dichloroethene. Environ. Sci. Technol. 38: 4300-4303.
4. He, J. 2003. Complete reductive dechlorination of chloroethenes to ethene and isolation of Dehalococcoides sp. strain BAV1. Ph.D. Thesis, Georgia Institute of Technology.
5. He, J., K. M. Ritalahti, M. R. Aiello, and F. E. Löffler. 2003. Complete detoxification of vinyl chloride (VC) by an anaerobic enrichment culture and identification of the reductively dechlorinating population as a Dehalococcoides species. Appl. Environ. Microbiol. 69: 996-1003.
6. He, J., K. M. Ritalahti, and F. E. Löffler. 2001. Characterization of a highly enriched culture that reductively dechlorinates vinyl chloride to ethene. Q-253, p. 634. In Abstracts of the 101st Annual Meeting of the American Society for Microbiology 2001. Orlando, FL.
7. He, J., K. M. Ritalahti, K.-L. Yang, S. S. Koenigsberg, and F. E. Löffler. 2003. Detoxification of vinyl chloride to ethene coupled to growth of an anaerobic bacterium. Nature 424: 62-65.
8. He, J., Y. Sung, M. E. Dollhopf, B. Z. Fathepure, J. M. Tiedje, and F. E. Löffler. 2002. Acetate versus hydrogen as direct electron donors to stimulate the microbial reductive dechlorination process at chloroethene-contaminated sites. Environ. Sci. Technol. 36: 2945-3952.
9. He, J., Y. Sung, R. Krajmalnik-Brown, K. M. Ritalahti, and F. E. Löffler. 2005. Isolation and characterization of Dehalococcoides sp. strain FL2, a trichloroethene (TCE)- and 1,2-dichloroethene-respiring anaerobe. Environ. Microbiol. 7: 1442-1450.
10. Hölscher, T., H. Görisch, and L. Adrian. 2003. Reductive dehalogenation of chlorobenzene congeners in cell extracts of Dehalococcoides sp. strain CBDB1. Appl. Environ. Microbiol. 69: 2999-3001.
11. Jayachandran, G., H. Gorisch, and L. Adrian. 2003. Dehalorespiration with hexachlorobenzene and pentachlorobenzene by Dehalococcoides sp strain CBDB1. Archives of Microbiology 180: 411-416.
12. Kube, M., A. Beck, S. H. Zinder, K. H., R. Reinhardt, and L. Adrian. 2005. Genome sequence of the chlorinated compound-respiring bacterium Dehalococcoides species strain CBDB1. Nat. Biotechnol. 23: 1269-1273.
13. Lendvay, J. M., F. E. Löffler, M. Dollhopf, M. R. Aiello, G. Daniels, B. Z. Fathepure, M. Gebhard, R. Heine, R. Helton, J. Shi, R. Krajmalnik-Brown, C. L. M. Jr., M. J. Barcelona, E. Petrovskis, J. M. Tiedje, and P. Adriaens. 2003. Bioreactive barriers: bioaugmentation and biostimulation for chlorinated solvent remediation. Environ. Sci. Technol. 37: 1422-1431.
14. Löffler, F. E., J. R. Cole, K. M. Ritalahti, and J. M. Tiedje. 2003. Diversity of dechlorinating bacteria, p. 53-87. In M. M. Häggblom and I. D. Bossert (ed.), Dehalogenation:   microbial processes and environmental applications. Kluwer Academic Press, New York, NY.
15. Major, D. W., M. L. McMaster, E. E. Cox, E. A. Edwards, S. M. Dworatzek, E. R. Hendrickson, M. G. Starr, J. A. Payne, and L. W. Buonamici. 2002. Field demonstration of successful bioaugmentation to achieve dechlorination of tetrachloroethene to ethene. Environ. Sci. Technol. 36: 5106-5116.
16. Maymó-Gatell, X., T. Anguish, and S. H. Zinder. 1999. Reductive dechlorination of chlorinated ethenes and 1,2-dichloroethane by ' Dehalococcoides ethenogenes ' 195. Appl. Environ. Microbiol. 65: 3108-3113.
17. Maymó-Gatell, X., Y.-T. Chien, J. M. Gossett, and S. H. Zinder. 1997. Isolation of a bacterium that reductively dechlorinates tetrachloroethene to ethene. Science 276: 1568-1571.
18. Maymó-Gatell, X., I. Nijenhuis, and S. H. Zinder. 2001. Reductive dechlorination of cis -dichloroethene and vinyl chloride by " Dehalococcoides ethenogenes ". Environ. Sci. Technol. 35: 516-521.
19. Ritalahti, K. M., and F. E. Löffler. 2004. Populations implicated in the anaerobic reductive dechlorination of 1,2-dichloropropane in highly enriched bacterial communities. Appl. Environ. Microbiol. 70: 4088-4095.
20. Seshadri, R., L. Adrian, D. E. Fouts, J. A. Eisen, A. M. Phillippy, B. A. Methe, N. L. Ward, W. C. Nelson, R. T. Deboy, H. M. Khouri, J. F. Kolonay, R. J. Dodson, S. C. Daugherty, L. M. Brinkac, S. A. Sullivan, R. Madupu, K. E. Nelson, K. H. Kang, M. Impraim, K. Tran, J. M. Robinson, H. A. Forberger, C. M. Fraser, S. H. Zinder, and J. F. Heidelberg. 2005. Genome sequence of the PCE-dechlorinating bacterium Dehalococcoides ethenogenes . Science 307: 105-108.