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Degradation of pentachlorophenol by Phanerochaete chrysosporium: intermediates and reactions involved

Department of Biochemistry and Molecular Biology, Oregon Graduate Institute of Science and Technology, 20000 NW Walker Road, Beaverton, OR 97006-8921, USA¹

Author for correspondence: Michael H. Gold. Tel: +1 503 748 1076. Fax: +1 503 748 1464. e-mail: mgold{at}bmb.ogi.edu

Under nitrogen-limiting, secondary metabolic conditions, the lignin-degrading basidiomycete Phanerochaete chrysosporium rapidly degrades pentachlorophenol. The pathway for the degradation of pentachlorophenol has been elucidated by the characterization of fungal metabolites and oxidation products generated by purified lignin peroxidase (LiP) and manganese peroxidase (MnP). The multi-step pathway is initiated by a LiP- or MnP-catalysed oxidative dechlorination reaction to produce tetrachloro-1,4-benzoquinone. Under primary or secondary metabolic conditions, the quinone is further degraded by two parallel pathways with cross-links. The quinone is reduced to tetrachlorodihydroxybenzene, which can undergo four successive reductive dechlorinations to produce 1,4-hydroquinone, and the latter is o-hydroxylated to form the final aromatic metabolite, 1,2,4-trihydroxybenzene. Alternatively, the tetrachloro-1,4-benzoquinone is converted, either enzymically or nonenzymically, to 2,3,5-trichlorotrihydroxybenzene, which undergoes successive reductive dechlorinations to produce 1,2,4-trihydroxybenzene. Finally, at several points, hydroxylation reactions convert chlorinated dihydroxybenzenes to chlorinated trihydroxybenzenes, linking the two pathways at each of these steps. Presumably, the 1,2,4-trihydroxybenzene produced in each pathway is ring-cleaved with subsequent degradation to CO₂. In contrast to the oxidative dechlorination step, the reductive dechlorinations and hydroxylations occur during both primary and secondary metabolic growth. Apparently, all five chlorine atoms are removed from the substrate prior to ring cleavage.

Keywords: pentachlorophenol, reductive dechlorination, hydroxylation, Phanerochaete chrysosporium, lignin and manganese peroxidases

Abbreviations: HC/HN, high carbon/high nitrogen; HC/LN, high carbon/low nitrogen; LiP, lignin peroxidase; MnP, manganese peroxidase; PCP, pentachlorophenol

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