Degradation of pentachlorophenol by Phanerochaete chrysosporium: intermediates and reactions involved

Under nitrogen-limiting, secondary metabolic conditions, the lignin-degradi ng basidiomycete Phanerochaete chrysosporium rapidly degrades pentachloroph enol. The pathway for the degradation of pentachlorophenol has been elucida ted by the characterization of fungal metabolites and oxidation products ge nerated by purified lignin peroxidase (LiP) and manganese peroxidase (MnP). The multi-step pathway is initiated by a LiP- or MnP-catalysed oxidative d echlorination reaction to produce tetrachloro-1,4-benzoquinone. Under prima ry or secondary metabolic conditions, the quinone is further degraded by tw o parallel pathways with cross-links. The quinone is reduced to tetrachloro dihydroxybenzene. which can undergo four successive reductive dechlorinatio ns to produce 1,4-hydroquinone, and the latter is o-hydroxylated to form th e final aromatic metabolite, 1,2,4-trihydroxybenzene. Alternatively, the te trachloro-1,4-benzoquinone is converted, either enzymically or nonenzymical ly, to 2,3,5-trichlorotrihydroxybenzene, which undergoes successive reducti ve dechlorinations to produce 1,2,4-trihydroxybenzene. Finally, at several points, hydroxylation reactions convert chlorinated dihydroxybenzenes to ch lorinated trihydroxybenzenes, linking the two pathways at each of these ste ps. Presumably, the 1,2.4-trihydroxybenzene produced in each pathway is rin g-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 c hlorine atoms are removed from the substrate prior to ring cleavage.