Degradation of 2,4-dichlorophenol by the lignin-degrading fungus Phanerochaete chrysosporium

Abstract

Under secondary metabolic conditions the white rot basidiomycete Phanerochaete chrysosporium mineralizes 2,4-dichlorophenol (I). The pathway for the degradation of 2,4-dichlorophenol (I) was elucidated by the characterization of fungal metabolites and of oxidation products generated by purified lignin peroxidase and manganese peroxidase. The multistep pathway involves the oxidative dechlorination of 2,4-dichlorophenol (I) to yield 1,2,4,5-tetrahydroxybenzene (VIII). The intermediate 1,2,4,5-tetrahydroxybenzene (VIII) is ring cleaved to produce, after subsequent oxidation, malonic acid. In the first step of the pathway, 2,4-dichlorophenol (I) is oxidized to 2-chloro-1,4-benzoquinone (II) by either manganese peroxidase or lignin peroxidase. 2-Chloro-1,4-benzoquinone (II) is then reduced to 2-chloro-1,4-hydroquinone (III), and the latter is methylated to form the lignin peroxidase substrate 2-chloro-1,4-dimethoxybenzene (IV). 2-Chloro-1,4-dimethoxybenzene (IV) is oxidized by lignin peroxidase to generate 2,5-dimethoxy-1,4-benzoquinone (V), which is reduced to 2,5-dimethoxy-1,4-hydroquinone (VI). 2,5-Dimethoxy-1,4-hydroquinone (VI) is oxidized by either peroxidase to generate 2,5-dihydroxy-1,4-benzoquinone (VII) which is reduced to form the tetrahydroxy intermediate 1,2,4,5-tetrahydroxybenzene (VIII). In this pathway, the substrate is oxidatively dechlorinated by lignin peroxidase or manganese peroxidase in a reaction which produces a p-quinone. The p-quinone intermediate is then recycled by reduction and methylation reactions to regenerate an intermediate which is again a substrate for peroxidase-catalyzed oxidative dechlorination. This unique pathway apparently results in the removal of both chlorine atoms before ring cleavage occurs.

Degradation of chlorophenoxyacetic acids by the lignin-degrading fungus Dichomitus squalens

“…In contrast, with ring-labelled substrate, the degradation rate is considerably greater in cultures grown under nitrogen-limiting conditions, suggesting that the degradation of the ring-labelled chlorophenol intermediates occurs under conditions of nitrogen depletion. We have shown previously that 2,4-DCP and 2,4,5-TCP are degraded by P. chrysosporium under nitrogen-limiting conditions (Valli & Gold, 1991;Joshi & Gold, 1993). These results suggest the involvement of ligninolytic enzymes in the degradation of the chlorinated phenolic intermediates, in agreement with results reported by Ryan & Bumpus (1989).…”

“…However, this is the first report of the formation of a xyloside of a chlorophenol in a wood-rotting basidiomycete. In P. chrysosporium chlorinated phenols undergo methylation to form their respective anisoles under secondary metabolic conditions (Lamar & Dietrich, 1990;Valli & Gold, 1991 ;Joshi & Gold, 1993). These chlorinated anisoles would be expected to be metabolically more stable than the corresponding xylosides reported herein, and this may at least partially account for the comparatively slower rate of chlorophenoxyacetic acid metabolism exhibited by P. chrysosporium (Fig.…”

“…We also have shown that the xylosides are hydrolysed to regenerate chlorophenols. The latter undergo oxidative dechlorination, catalysed by manganese peroxidase, and subsequent ring cleavage (Valli & Gold, 1991 ;Joshi & Gold, 1993). We are attempting to…”

“…chrysosporium, the chlorophenols are methylated to form their corresponding anisoles (Lamar & Dietrich, 1990;Valli & Gold, 1991;Joshi & Gold, 1993). We also have shown that the xylosides are hydrolysed to regenerate chlorophenols.…”

“…Recent studies have demonstrated that P. chrysosporium is able to degrade many chlorinated aromatic pollutants, including di, tri-and pentachlorophenols, chlorinated dibenzodioxins and chlorinated phenoxyacetic acids, and that Lip and MnP are involved in the initial degradative steps (Bumpus & Aust, 1987;Hammel, 1989;Ryan & Bumpus, 1989;Valli & Gold, 1991;Valli et al, 1992;Yadav & Reddy, 1992Joshi & Gold, 1993). Several intracellular enzymes from P. chrysosporium mycelial extracts, including a quinone reductase and a ring-opening dioxygenase, have also been purified and characterized (Rieble et al, 1994;Brock et al, 1995;Brock & Gold, 1996).…”