4-Chlorobiphenyl has been used as a model substrate to investigate polychlorinated biphenyl (PCB) degradation by aerobic bacteria. PCBs are a class of very stable synthetic organic compounds composed of a biphenyl nucleus with 1-10 chlorine substituents. There are 209 different PCB congeners, of which 132 have been identified in different commercial mixtures. PCBs are environmentally persistent, bioaccumulate in food chains and are potentially toxic, prompting efforts to clean up contaminated sites. Bioremediation is being considered as a cheaper, less disruptive and more publicly acceptable alternative to current remediation technologies such as incineration. The EAWAG-BBD also contains the Biphenyl Pathway, which is considered as the degradation model for various PCBs.
4-Chlorobiphenyl is degraded similarly to biphenyl, with 2,3-dioxygenation at the unsubstituted biphenyl ring, followed by rearomatization, and cleavage of this catachol-like ring (Fukuda et al., 1994).
The following is a text-format 4-Chlorobiphenyl 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 (13k) format.
4-Chlorobiphenyl
Pseudomonas sp. strain LB400
Pseudomonas pseudoalcaligenes KF707
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| biphenyl dioxygenase
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v
cis-2,3-Dihydro-2,3-dihydroxy-4'-chlorobiphenyl
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| cis-2,3-dihydro-2,3-dihydroxybiphenyl dehydrogenase
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v
2,3-Dihydroxy-4'-chlorobiphenyl
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| 2,3-dihydroxybiphenyl-1,2-dioxygenase
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v
2-Hydroxy-6-oxo-6-(4'-chlorophenyl)-hexa-2,4-dienoate
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| 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoate hydrolase
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v
4-Chlorobenzoate + 2-Hydroxypenta-2,4-dienoate <---- from the
| | p-Cymene, Biphenyl, and
| | Fluorene Pathways
| | 2-hydroxy-
| | 2,4-pentadienoate
| | hydratase
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v v
to the 4-Hydroxy-2-oxovalerate
2,4-Dichlorobenzoate |
Pathway |
| 4-hydroxy-2-
| oxovalerate
| aldolase
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v
Acetaldehyde + Pyruvate
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v v
Intermediary Intermediary
Metabolism Metabolism
(KEGG) (KEGG)
Page Author(s): Shou-Lin Chang and Dong Jun Oh
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