Metabolic pathways utilized by Phanerochaete chrysosporium for degradation of the cyclodiene pesticide endosulfan

Abstract

Recent studies have shown that cultures of white rot fungi not favoring the production of lignin and manganese peroxidases are effective in degrading certain xenobiotics. In this study we have used endosulfan as a model xenobiotic to assess the enzymatic mechanisms of pesticide metabolism under ligninolytic (nutrient-deficient) and nonligninolytic (nutrient-rich) culture conditions. Rapid metabolism of this chlorinated pesticide occurred under each nutrient condition tested. However, the extent of degradation and the nature of the metabolic products differed for nutrient-deficient and nutrient-rich media. The pathways for endosulfan metabolism were characterized by analysis of the fungal metabolites produced. The major endosulfan metabolites were identified by gas chromatography-electron capture detection and gas chromatography-mass spectrometry as endosulfan sulfate, endosulfan diol, endosulfan hydroxyether, and a unknown metabolite tentatively identified as endosulfan dialdehyde. The nature of the metabolites formed indicates that this organism utilizes both oxidative and hydrolytic pathways for metabolism of this pesticide. Piperonyl butoxide, a known cytochrome P-450 inhibitor, significantly inhibited the oxidation of endosulfan to endosulfan sulfate and enhanced hydrolysis of endosulfan to endosulfan diol. We suggest that the metabolism of endosulfan is mediated by two divergent pathways, one hydrolytic and the other oxidative. Judging by the inactivity of extracellular fluid and partially purified lignin peroxidase in metabolizing endosulfan, we conclude that metabolism of this compound does not involve the action of extracellular peroxidases.