Biodegradation of benzo(a)pyrene by Marasmiellus troyanus and formulation for bioremediation
Description
Polyaromatic hydrocarbons and their various transformation products constitute a serious environmental and biological hazard. Benzo(a)pyrene, (B(a)P), a polycyclic aromatic hydrocarbon, is an acutely toxic, carcinogenic and recalcitrant industrial pollutant that enters the environment as a byproduct of petroleum refining and combustion. Traditionally, decontamination schemes have used chemical or physical methods, but during the last two decades, there has been an increasing interest in bioremediation Seventeen fungi were screened with tannic and gallic acid plate assays along with the polymeric dye R-478 decolorization assays for presumptive extracellular ligninase activity. Dye decolorization was correlated with B(a)P degradation for mycelia and extracellular filtrates. Marasmiellus troyanus, a litter rot fungus isolated from a petroleum contaminated Superfund site, and the well-studied white rot fungus, Phanerochaete chrysosporium, were chosen for further study Respectively, ELISA and mass balance analyses studies confirm the production of lignin peroxidases and manganese-dependent peroxidases by P. chrysosporium, and show this fungus is effective in metabolizing (12.9%) and mineralizing, (1.2%) B(a)P under ligninolytic conditions. Comparatively, M. troyanus metabolized (72.4%) and mineralized (8.4%) B(a)P more efficiently but without detectable peroxidases. M. troyanus degraded B(a)P in two phases. The first phase was associated with extracellular enzymatic activity and correlated to the degradation pattern of P P. chrysosporium, while the second phase was unique to M. troyanus. Furthermore, GC-MS analyses show that M. troyanus initially oxidizes B(a)P to form a phenol. We also detected the formation of a dihydrodiol and an unidentified metabolite conjugated with either glucuronic acids or sulfates The effective introduction of fungi into a bioremediation scenario is dependent upon the mass production of inoculum for application to the contaminated site. M. troyanus, encapsulated in alginate, remained viable for two years in refrigerated storage. Mass balance analyses showed that these alginate beads effectively metabolized B(a)P (64.4%) but no mineralization was detected. Nevertheless, this study indicates that the delivery of M. troyanus to soils and sludges contaminated with petroleum aromatic hydrocarbons using alginate encapsulation is a feasible and promising strategy