Optimization of Laccase-mediated Benzo[a]pyrene Oxidation and the Bioremedial Application in Aged Polycyclic Aromatic Hydrocarbons-contaminated Soil

Laccase is a polyphenol oxidase with the ability to oxidize a broad range of persistent organic pollutants, including benzo[a]pyrene, the most carcinogenic, mutagenic and teratogenic polycyclic aromatic hydrocarbons (PAHs). In this study, the reaction conditions for benzo[a]pyrene oxidation by laccase from Trametes versicolor were optimized in a liquid medium by a series of single factor experiments. The maximal benzo[a]pyrene oxidation rate was observed at 40°C, pH 4, 10% of acetonitrile and an incubation time of more than 24hr, and the benzo[a]pyrene oxidation was enhanced significantly by the addition of a mediator, 2,2-azino-bis-(3-ethylbenzothiazoline-6-sulfonicacid) (ABTS). Laccase was also applied to aged PAHs polluted soil to examine the efficiency of enzymatic bioremediation. The results showed that the enzyme was still effective in the degradation of anthracene, benzo[a]pyrene and benzo[a]anthracene in soil. Moreover, the degradation rate of most PAHs increased by the addition of ABTS. Our results indicated that the bioremediation of PAHs contaminated soil using laccase is feasible but a suboptimal pH might be a limiting factor in the enzymatic treatment of soil.