| High molecular weight (MW) polycyclic aromatic hydrocarbons (PAHs) are byproducts of the incomplete combustion of fossil fuels. Many high MW PAHs are genotoxic and can persist in contaminated soils for years, posing a hazard to ecosystem health. Microbial degradation processes are the major mechanism of PAH removal from soils, therefore understanding these pathways is a prerequisite for bioremediation of contaminated soils.;Fungi were isolated from petroleum-contaminated soils and pure cultures were screened for pyrene-oxidizing ability using chromatographic analyses of ethyl acetate culture extracts. Approximately 50% of the isolates, including deuteromycetes, zygomycetes and ascomycetes, were capable of oxidizing pyrene, primarily by the following pathway: pyrene → 1-pyrenol → 1,6- +1,8-dihydroxypyrene → 1,6- +1,8-pyrenequinone. Half of the pyrene-oxidizing fungi also oxidized benzo[a]pyrene to 9-hydroxybenzo[a]pyrene. This suggests that a common enzyme system, probably a cytochrome P450 monooxygenase, oxidizes both PAHs.;The conversion of pyrene to pyrenequinones (PQs) by pure cultures of the selected isolate P. janthinellum SFU403 (ATCC;Mass balance studies using 14C-pyrene demonstrated that PQs are not terminal metabolites in cultures of P. janthinellum SFU403. After two weeks of incubation, approximately 100% of 14C-pyrene formed inextractable cell-associated products (ICAP); 21--44% was related to PQ formation and the remainder was due to sorption of unreacted pyrene to the fungal biomass. To determine whether PQs could form ICAP via a pyrene semiquinone (PSQ) anion radical intermediate, electron paramagnetic resonance spectroscopy was used to detect the formation of PSQs in vitro. Under anaerobic conditions, physiological concentrations of NADPH reduced both pyrene 1,8- and 1,6-quinones to the corresponding PSQs. Furthermore, oxygen consumption was enhanced when PQs were incubated with NADPH or glutathione in vitro, indicating that PSQs can redox cycle with O2. The importance of PSQ formation in vivo remains to be established. These studies represent one of the first characterizations of high MW PAH-degradation by a Penicillium sp. |
