Degradation of isoproturon by the white rot fungus Phanerochaete chrysosporium

The ability of the white rot fungus Phanerochaete chrysosporium to degrade isoproturon was tested in solid substrate fermentation (SSF) cultures using straw as substrate/carrier material. The role of the lignin degrading enzymes, lignin peroxidase (LiP) and manganese peroxidase (MnP), in the degradation of the herbicide was also studied. Isoproturon concentration and LiP and MnP activities were followed in sterile straw cultures of the fungus. In vitro degradation tests with pure LiP and MnP were performed. P. chrysosporium in straw cultures was able to degrade 91% of the herbicide isoproturon in 14 days of incubation. A sharp decrease of isoproturon coincided with the largest MnP activity. Although LiP activity was also present, its role in SSF is unclear. The in vitro tests showed a strong isoproturon oxidation by LiP and a slower oxidation by MnP in the presence of Tween 80 probably by a lipid peroxidation process. Two N-demethylated metabolites were identified in pure enzyme tests and in SSF cultures. Several unidentified isoproturon derivatives, most likely hydroxylated, were also formed in both systems. The different pattern of derivatives detected in pure LiP and MnP tests showed a completely different metabolism by these two enzymes.