Polycyclic aromatic hydrocarbon metabolism by the white-rot fungus Bjerkandera adusta and oxidation by manganese peroxidase

Polycyclic aromatic hydrocarbons are typically found in creosote, oils, tars and sites contaminated with theses products: they are produced by incomplete combustion of organic carbon compounds. They are toxic pollutants and the research project was to investigate their metabolism as a means of bioremediation. White-rot fungi and their extracellular enzymes, which have the ability to degrade the naturally occurring polymer lignin, have been evaluated for their potential to degrade polycyclic aromatic hydrocarbons. We have shown that two Bjerkandera adusta strains from the University of Alberta Microfungus Collection and Herbarium (UAMH) 8258 and 7308 are active in polycyclic aromatic hydrocarbon degradation.;Grown under ligninolytic conditions, B. adusta UAMH 8258 and 7308 produce only manganese peroxidase, and under optimal conditions, B. adusta UAMH 8258 and 7308 can produce high levels of manganese peroxidase in both shake flasks and stirred tank reactors, indicating that these two strains are good candidates for large scale enzyme production.;Manganese peroxidase from B. adusta 8258 was purified and characterized. The enzyme exhibited both Mn(II)-dependent and Mn(II)-independent activity, different from manganese peroxidase from Phanerochaete chrysosporium . The purified enzyme was modified with cyanuric chloride-activated methoxypolyethylene glycol and the modified enzyme showed greater resistance to denaturation by hydrogen peroxide, presence of organic solvents, high temperature and low pH.;Polycyclic aromatic hydrocarbon oxidation was studied using whole cells and purified manganese peroxidase from B. adusta UAMH 8258. Polycyclic aromatic hydrocarbon oxidation by the purified enzyme was reduced by the presence of Mn(II) and the inhibition kinetics were shown to be partially noncompetitive. The substrates oxidized by manganese peroxidase were anthracene, and its methyl derivatives, pyrene, and benzo[a]pyrene: polycyclic aromatic hydrocarbons with ionization potentials of 7.43 eV or lower. The polycyclic aromatic hydrocarbon metabolites of the Mn(II)-independent reaction were identified as the corresponding quinones. The chemically modified enzyme had an enhanced oxidation rate compared with the native enzyme. Polycyclic aromatic hydrocarbon metabolism by cultures of B. adusta UAMH 8258 showed no clear differences between ligninolytic and nonligninolytic conditions, indicating the involvement of both intracellular and extracellular enzymes. Although B. adusta UAMH 8258 was able to cometabolize all the tested polycyclic aromatic hydrocarbons, only limited mineralization occurred.