beta-1,2,3,4,5,6-Hexachlorocyclohexane (an/anerobic) Pathway Map

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This pathway was started by Peter Middeldorp, Wageningen Agricultural University, The Netherlands, and completed by Ryan McLeish, Meaghan Fitzgerald and Michael Turnbull, University of Minnesota.

During the production of the pesticide Lindane (gamma-hexachlorocyclohexane (HCH)), about 85% of the product consisted of isomers such as alpha-, beta- and delta-HCH. They were discarded into the environment, causing serious soil pollution. Aerobic biodegradation mineralizes alpha-, gamma-, and delta-HCH, whereas beta-HCH persists. Therefore, the degradation of beta-HCH and the other isomers was studied under anaerobic conditions by Peter Middeldorp (Environmental Science and Technology (1996) 30(7):2345-2349), in order to develop an anaerobic soil treatment process. beta-HCH was found to anaerobically biodegrade to benzene and chlorobenzene, both of which can undergo further degradation aerobically. The pathway from beta-HCH to benzene and chlorobenzene is the first anaerobic pathway in the EAWAG-BBD. This pathway can be carried out by a Dehalobacter sp. in coculture with a Sedimentibacter sp. (van Doesburg et al., 2005).

A second, aerobic, beta-HCH metabolic pathway is mediated by haloalkane dehalogenase LinB in Sphingomonas paucimobilis UT26. The stereochemistry of the 2,3,4,5,6-pentachlorocyclohexanol has not been determined; the stereoisomer shown is based on beta-HCH. The pentachlorocyclohexane is not further metabolized (Nagata et al., 2004).

The biodegradation pathway for gamma-hexachlorocyclohexane is found elsewhere.

The following is a text-format beta-1,2,3,4,5,6-hexachlorocyclohexane pathway map. Follow the links for more information on compounds or reactions. This map is also available in graphic (13k) format.

                            beta-1,2,3,4,5,6-Hexachlorocyclohexane                        beta-1,2,3,4,5,6-Hexachlorocyclohexane
                                      Dehalobacter sp.                                        Sphingomonas paucimobilis UT26
                                     Sedimentibacter sp.                                                     |
                                              |                                                              | haloalkane
                                              | A                                                            | dehalogenase
                                              |                                                              |
                                              v                                                              v
                        +--- delta-3,4,5,6-Tetrachlorocyclohexene ---+                       2,3,4,5,6-Pentachlorocyclohexanol
                        |                                            |
                        | B                                          | C
                        |                                            |
                        v                                            v                 
                  [5,6-Dichloro-                               [5,6-Dichloro-
	       1,3-cyclohexadiene]                          1,3-cyclohexadiene]        
                        |                                            |
                        |                                            |
    from the            v                                            v          
 Organomercury ----> Benzene                                   Chlorobenzene
      and               |                                            |           
  Triphenyltin          | benzene 1,2-dioxygenase                    |              
    Pathways            |                                            |   
                        |                                            v
                        v                                          to the
              cis-Dihydrobenzenediol                       Chlorobenzene Pathway
                        | cis-1,2-dihydrobenzene-
                        | 1,2-diol dehydrogenase
                     to the

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Page Author(s): Peter Middeldorp, Ryan McLeish, Meaghan Fitzgerald and Michael Turnbull

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