Metabolism of phenanthrene by the white rot fungus Pleurotus ostreatus

The white rot fungus Pleurotus ostreatus, grown for 11 days in basidiomycetes rich medium containing [¹⁴C] phenanthrene, metabolized 94% of the phenanthrene added. Of the total radioactivity, 3% was oxidized to CO₂. Approximately 52% of phenanthrene was metabolized to trans-9,10- dihydroxy-9,10-dihydrophenanthrene (phenanthrene trans-9,10-dihydrodiol) (28%), 2,2'-diphenic acid (17%), and unidentified metabolites (7%). Nonextractable metabolites accounted for 35% of the total radioactivity. The metabolites were extracted with ethyl acetate, separated by reversed-phase high-performance liquid chromatography, and characterized by ¹H nuclear magnetic resonance, mass spectrometry, and UV spectroscopy analyses. ¹⁸O₂- labeling experiments indicated that one atom of oxygen was incorporated into the phenanthrene trans-9,10-dihydrodiol. Circular dichroism spectra of the phenanthrene trans-9,10-dihydrodiol indicated that the absolute configuration of the predominant enantiomer was 9R,10R, which is different from that of the principal enantiomer produced by Phanerochaete chrysosporium. Significantly less phenanthrene trans-9,10-dihydrodiol was observed in incubations with the cytochrome P-450 inhibitor SKF 525-A (77% decrease), 1-aminobenzotriazole (83% decrease), or fluoxetine (63% decrease). These experiments with cytochrome P-450 inhibitors and ¹⁸O₂ labeling and the formation of phenanthrene trans-9R,10R-dihydrodiol as the predominant metabolite suggest that P. ostreatus initially oxidizes phenanthrene stereoselectively by a cytochrome P-450 monoxygenase and that this is followed by epoxide hydrolase- catalyzed hydration reactions.