White-rot Fungi Screening For Efficient Degradation Of Pahs-phenanthrene And Preliminary Study On The Degradation Mechanism

PAHs are large closely watched, persistent environmental pollutants, because of its strong teratogenic, carcinogenic and mutagenic effect in recent decades gradually attracted people’s attention. Phenanthrene is the smallest structural unit of carcinogenic PAHs and so often as a microbial degradation of PAHs research model. White rot fungi become a major microbial source of the remediation of the environmental pollution aspects due to its unique degradation mechanism, extracellular degradation characteristics. White rot fungi play an unparalleled role in the field of environmental protection. This paper attempted to screen one kind capable of degrading phenanthrene from10kinds of white-rot fungi. Study on phenanthrene degradation characteristics and degradation conditions optimization of the species. Finally, analysis of its phenanthrene degradation intermediates, speculated that species metabolic pathways.In this study, using liquid shake flask culture, screened one species from10kinds of white-rot fungi can effectively degradation of phenanthrene. Cultured16days, there were4kinds which phenanthrene degradation rate above50%, Pleurotus eryngii’s degradation rate reached80.11%. The results of the study on laccase activity and phenanthrene degradation rate of different species showed that the laccase activity secretion and the degradation rate are related. Study of impact of phenanthrene adding to medium showed that the right amount of added phenanthrene can promote laccase secretion, the peak activity increases, but also makes a certain degree of activity peaks after the extension. Research on biomass and medium residual concentration of phenanthrene showed that the Pleurotus eryngii biomass began to decline after12days, the phenanthrene residual concentration of the medium stabilized. At phenanthrene concentration of800mg/L, the Pleurotus eryngii’s growth was not affected, the cell of Pleurotus eryngii showed a higher ability to withstand phenanthrene.After the optimization of the conditions of the degradation of phenanthrene by the Pleurotus eryngii, we obtained better conditions were as follows:2%glucose,20%potatoes,0.5%yeast extract, inoculums at2pieces, liquid volume at30mL/100mL conical flask, the culture temperature at28℃, speed at140r/min, initially pH at6.0, inducer of CMC-Na0.5g/L, the number of degrading days at12days, adding to potato which impactting the degradation of the phenanthrene. According to Plackett-Burman experimental results, we found that potatoes concentration in the medium, liquid volume, and culture temperature had a significant effect on the degradation rate of phenanthrene. Using response surface methodology for optimizing potatoes concentration in the medium, liquid volume, and culture temperature to obtain the optimal combination of three conditions were as follows:potato concentration214g/L, liquid volume30.4mL/100mL conical flask, culture temperature at27℃. Under the conditions, the phenanthrene theory degradation rate reached80.68%.The study of the effects on laccase activity of removal of phenanthrene and metal ions showed that the degradation occupy major proportion, there are certain cells adsorption, Cu2+and lignin to promoting the Pleurotus eryngii’s laccase activity was more apparent. The study of the phenanthrene degradation mechanism showed that the laccase played a significant role in the degradation of the phenanthrene. Finally through GC-MS analysis, the Pleurotus eryngii middle metabolites were identified, the analysis of these metabolites suggestted that the intermediate metabolites of degradation phenanthrene were varietied, the degradation mechanism was very complex and there were several possible metabolic pathways.