Gvb. Reddy et Mh. Gold, Degradation of pentachlorophenol by Phanerochaete chrysosporium: intermediates and reactions involved, MICROBIO-UK, 146, 2000, pp. 405-413
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.