Tetrachloroethene, also known industrially as perchloroethylene (PCE), is a good solvent used to clean machinery, electronic parts, and clothing. It and trichloroethene (TCE) are suspected carcinogens and some of the most abundant environmental pollutants of groundwater in the United States. In some groundwater, they undergo reductive dechlorination catalyzed by anaerobic bacteria that yields vinyl chloride, a potent human carcinogen. Removal by dumping or air stripping is now largely disallowed and this has focused efforts on biological methods of PCE and TCE remediation in soil and water. Aerobic TCE biodegradation pathways are found in the EAWAG-BBD.
Anaerobic pathways are less well-understood. Only the first enzyme in this pathway has been isolated; in Dehalospirillum multivorans it also catalyzes the reductive dehalogenation of trichloroethene to cis-1,2-dichloroethene (Neumann et al., 1996). Other organisms implicated in anerobic PCE biodegradation include Sporomusa ovata (Terzenbach & Blaut, 1994), and Dehalobacter restrictus TEA (Wild et al., 1996). Most organisms studied convert trichloroethene to cis-1,2-dichloroethene (DCE); Dehalococcoides ethenogenes 195 is reported to also produce the trans isomer. TCE can be reductively dehalogenated (through both cis and trans DCE) by the CO dehydrogenase from Methanosarcina thermophila (Jablonski & Ferry, 1992). All reactions in Dehalococcoides ethenogenes 195, as well as the name of this organism, are proposed (Maymo-Gatell et al., 1997).
The following is a text-format anerobic tetrachloroethene pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (9k) format.
Tetrachloroethene (PCE) Dehalococcoides ethenogenes 195 Dehalospirillum multivorans Sporomusa ovata Dehalobacter restrictus TEA Desulfitobacterium sp. PCE-S | | tetrachloroethene | reductive dehalogenase | v +----------------- TCE --------------------------+ | only D. ethenogenes 195 | | | | | trichloroethene | trichloroethene | | reductive | reductive | | dehalogenase | dehalogenase | | | | | | | v v | cis-1,2-Di- [trans-1,2-Di- | chloroethene chloroethene] | | | | | | | | dichloroethene | dichloroethene | trichloroethene | reductive | reductive | reductive | dehalogenase | dehalogenase | dehalogenase | | | | | | | v | +----> Vinyl chloride | | | | vinyl chloride | | reductive dehalogenase | | | v | Ethylene <-----------------------------+ | | v to the Acetylene Pathway
Page Author(s): Lynda Ellis and Sean Anderson
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