Immobilization of laccase from trametes versicolor on chitosan macrobeads for anthracene degradation

Anthracene bioconversion was achieved by immobilized enzyme technology. An oxidation yield of 0.7 mg/L of polycyclic aromatic hydrocarbons reached 60% following 24 h of incubation with laccase from Trametes versicolor covalently immobilized on glutaraldehyde-activated chitosan at the optimal pH of 5 in the presence of diammonium 2,2-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) as the radical mediator. High-performance liquid chromatography indicated that the main product of anthracene oxidation was 9,10-anthraquinone which is less toxic than its precursor. Highly porous 3 mm diameter chitosan macrobeads were synthesized by precipitation in alkaline solution. Support activation with glutaraldehyde was confirmed by elemental analysis, thermogravimetry, and infrared spectroscopy. The bioreactor system was characterized for kinetic parameters obtaining a Michaelis–Menten constant of 0.13 mM and a maximum rate of 0.0011 µmol/min/mg, thermal stability, and reuse. The protein and glutaraldehyde concentrations were optimized to enhance the efficiency of the bioreactor.