Oxidative degradation of polyaromatic hydrocarbons catalyzed by blue laccase from Pleurotus ostreatus D1 in the presence of synthetic mediators

The laccase produced by the white-rot fungus Pleurotus ostreatus D1 (BLPO) under submerged cultivation was purified to homogeneity. Its catalytic activity towards several phenolic compounds, including ABTS (2,2′-azino-bis-(3-ethylbenzthiazoline-6-sulphonic acid) diammonium salt), syringaldazine (4-hydroxy-3,5-dimethoxybenzaldehyde azine), 2,6-dimethoxyphenol and catechol was investigated. pH-optima and kinetic constants (Km and Vmax) of these reactions were determined. The enzyme was able to degrade the following polyaromatic hydrocarbons (PAHs): anthracene (91%), phenanthrene (72%), fluorene (53.5%), pyrene (65.5%), fluoranthene (69.7%), and perylene (73%) only in the presence of a synthetic mediator. The degradation of phenanthrene in the presence of detergents varied from 49% to 72%, whereas in the absence of any detergent it reached 10%. Investigating the effect of various mediators on PAHs degradation by the BLPO showed that ABTS was a better mediator of anthracene oxidation and HBT (1-hydroxybenzotriazole) was a better mediator of fluorene oxidation. Pyrene and anthracene were degraded more rapidly in a mixture than separately. The effect of different solvents on the activity of the BLPO towards anthracene and fluorene was investigated also. Finally, it was found that in a solution of 30% (v/v) acetonitrile, BLPO could degrade about 56% of the 600 μM initially added anthracene with the formation of anthraquinone.