Degradation of Benzo[ a ]pyrene by the Litter-Decomposing Basidiomycete Stropharia coronilla : Role of Manganese Peroxidase

Abstract

ABSTRACT The litter-decomposing basidiomycete Stropharia coronilla , which preferably colonizes grasslands, was found to be capable of metabolizing and mineralizing benzo[ a ]pyrene (BaP) in liquid culture. Manganese(II) ions (Mn 2+ ) supplied at a concentration of 200 μM stimulated considerably both the conversion and the mineralization of BaP; the fungus metabolized and mineralized about four and twelve times, respectively, more of the BaP in the presence of supplemental Mn 2+ than in the basal medium. This stimulating effect could be attributed to the ligninolytic enzyme manganese peroxidase (MnP), whose activity increased after the addition of Mn 2+ . Crude and purified MnP from S. coronilla oxidized BaP efficiently in a cell-free reaction mixture (in vitro), a process which was enhanced by the surfactant Tween 80. Thus, 100 mg of BaP liter −1 was converted in an in vitro reaction solution containing 1 U of MnP ml −1 within 24 h. A clear indication was found that BaP-1,6-quinone was formed as a transient metabolite, which disappeared over the further course of the reaction. The treatment of a mixture of 16 different polycyclic aromatic hydrocarbons (PAHs) selected by the U.S. Environmental Protection Agency as model standards for PAH analysis (total concentration, 320 mg liter −1 ) with MnP resulted in concentration decreases of 10 to 100% for the individual compounds, and again the stimulating effect of Tween 80 was observed. Probably due to their lower ionization potentials, poorly bioavailable, high-molecular-mass PAHs such as BaP, benzo( g , h , i )perylene, and indeno(1,2,3- c , d )pyrene were converted to larger extents than low-molecular-mass ones (e.g., phenanthrene and fluoranthene).