g-Hexachlorocyclohexane (g-HCH, BHC, lindane) is a halogenated
organic insecticide that has been used worldwide for agriculture and public
Because of its high toxicity and persistence in soil, the use of g-HCH
has been prohibited in many countries. g-HCH is degraded rapidly under
anaerobic conditions, but is considered extremely persistent
in upland soil. Sphingomonas
(formerly Pseudomonas) paucimobilis SS86 was isolated
from an upland experimental field to which g-HCH was applied once a
year for twelve years. The mutant of the strain SS86, named UT26, has
nalidixic acid resistance as a genetic marker and utilizes g-HCH as a sole source
of carbon and energy under aerobic conditions. The genes and enzymes
involved in the g-HCH degradation pathway of S. paucimobilis UT26 have been investigated
(Imai et al., 1991; Nagata et al., 1999, J. Ind. Microbiol. Biotechnol. 23: 380-390).
The cyanobacteria Anabeana sp. PCC7120 and Nostoc ellipsosporum have also been shown to metabolize lindane. A mixture of 1,2,4- and 1,2,3-trichlorobenzenes is produced (Kuritz and Wolk, 1995).
The absolute configuration of 2,4,5-Trichloro-2,5-cyclohexadiene-1-ol and 2,5-Dichloro-2,5-cyclohexadiene-1,4-diol have not yet been determined. The biodegradation pathway for beta-hexachlorocyclohexane is found elsewhere.
The following is a text-format gamma-Hexachlorocyclohexane 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 (18K) format.
gamma-Hexachlorocyclohexane (g-HCH) Sphingomonas paucimobilis UT26 Anabaena sp. PCC7120 Nostoc ellipsosporum | | 1,2,3-Trichlorobenzene | g-HCH dehydrochlorinase ^ | | | | C v Anabaena sp. PCC7120 ^ 1,3(R),4(S),5(S),6(R)- Nostoc ellipsosporum | Pentachlorocyclohexene -----------------------------+ (g-PCCH) | | | | v D | g-HCH dehydrochlorinase | | | | | v A v 1,3(R),4,6(R)-Tetrachloro-1,4- ------> 1,2,4-Trichlorobenzene cyclohexadiene (1,4-TCDN) (1,2,4-TCB) | | | | | haloalkane dehalogenase v | to the 1,2,4-TCB Pathway | v B 2,4,5-Trichloro-2,5- ------> 2,5-Dichlorophenol cyclohexadiene-1-ol (2,4,5-DNOL) (2,5-DCP) | | | haloalkane dehalogenase | | v 2,5-Dichloro-2,5-cyclohexadiene -1,4-diol (2,5-DDOL) | | | 2,5-DDOL dehydrogenase | | v 2,5-Dichlorohydroquinone ------> to the 2,4,5-T Pathway (2,5-DCHQ) | | | 2,5-DCHQ reductive dehalogenase | | v Chlorohydroquinone (CHQ) | | | 2,5-DCHQ reductive dehalogenase | | v Hydroquinone (HQ) | | | | | v to the 4-Nitrophenol Pathway
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