DEGRADATION OF 2,4,5-TRICHLOROPHENOL BY THE LIGNIN-DEGRADING BASIDIOMYCETE PHANEROCHAETE-CHRYSOSPORIUM

Under secondary metabolic conditions the white rot basidiomycete Phane rochaete chrysosporium rapidly mineralizes 2,4,5-trichlorophenol. The pathway for degradation of 2,4,5-trichlorophenol was elucidated by the characterization of fungal metabolites and oxidation products generat ed by purified lignin peroxidase (LiP) and manganese peroxidase (MnP). The multistep pathway involves cycles of peroxidase-catalyzed oxidati ve dechlorination reactions followed by quinone reduction reactions to yield the key intermediate 1,2,4,5-tetrahydroxybenzene, which is pres umably ring cleaved. In the first step of the pathway, 2,4,5-trichloro phenol is oxidized to 2,5-dichloro-1,4-benzoquinone by either MnP or L iP. 2,5-Dichloro-1,4-benzoquinone is then reduced to 2,5-dichloro-1,4- hydroquinone. The 2,5-dichloro-1,4-hydroquinone is oxidized by MnP to generate 5-chloro-4-hydroxy-1,2-benzoquinone. The orthoquinone is in t urn reduced to 5-chloro-1,2,4-trihydroxybenzene. Finally, the 5-chloro trihydroxybenzene undergoes another cycle of oxidative dechlorination and reduction reactions to generate 1,2,4,5-tetrahydroxybenzene. The l atter is presumably ring cleaved, with subsequent degradation to CO2. In this pathway, the substrate is oxidatively dechlorinated by LiP or MnP in a reaction which produces a quinone. The quinone intermediate i s recycled by a reduction reaction to regenerate an intermediate which is again a substrate for peroxidase-catalyzed oxidative dechlorinatio n. This pathway apparently results in the removal of all three chlorin e atoms before ring cleavage occurs.