DEGRADATION OF CHLOROPHENOXYACETIC ACIDS BY THE LIGNIN-DEGRADING FUNGUS DICHOMITUS SQUALENS

We have examined the degradation of C-14 ring- and side-chain-labelled 2,4,5-trichlorophenoxyacetic acid by Dichomitus squalens and Phaneroc haete chrysosporium. The effects of Mn2+ on the degradation of these r adiolabelled substrates by D. squalens and the effect of nitrogen limi tation on their degradation by P. chrysosporium suggested that in both fungi, side-chain cleavage was catalysed by a mechanism independent o f the lignin degradation system, whereas the degradation of the aromat ic ring was dependent on the lignin degradative system. Using unlabell ed substrates, a pathway for the degradation of chlorophenoxyacetic ac ids was elucidated in D. squalens. Time courses for the degradation of unlabelled chlorophenoxyacetic acids by D. squalens demonstrated that the corresponding chlorophenol was the initial product formed. The ch lorophenol intermediate was xylosylated to form the chlorophenolxylosi de. In turn, the chlorophenolxyloside could be hydrolysed by an intrac ellular beta-xylosidase to regenerate the chlorophenol. The chlorophen ol product of the xylosidase reaction was oxidatively dechlorinated to form 2-chloro-p-benzoquinone which could undergo subsequent further d echlorination and ring-opening reactions, as has been reported previou sly for P. chrysosporium.