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Applied and Environmental Microbiology, July 2003, p. 3957-3964, Vol. 69, No. 7
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.7.3957-3964.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

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

Kari T. Steffen,1* Annele Hatakka,1 and Martin Hofrichter2

Division of Microbiology, Department of Applied Chemistry and Microbiology, University of Helsinki, FIN-00014 Helsinki, Finland,1 Unit of Environmental Biotechnology, International Graduate School Zittau, D-02763 Zittau, Germany2

Received 23 December 2002/ Accepted 28 April 2003

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 (Mn2+) 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 Mn2+ 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 Mn2+. 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).

* Corresponding author. Mailing address: Department of Applied Chemistry and Microbiology, P.O. Box 56, Biocenter 1, Viikinkaari 9, FIN-00014 Helsinki, Finland. Phone: 358 9 191 59321. Fax: 358 9 191 59322. E-mail: kari.steffen{at}helsinki.fi.

Applied and Environmental Microbiology, July 2003, p. 3957-3964, Vol. 69, No. 7
0099-2240/03/$08.00+0     DOI: 10.1128/AEM.69.7.3957-3964.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.





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