Oxidation of anthracene and benzo[a]pyrene by immobilized laccase from Trametes versicolor

Polycyclic aromatic hydrocarbons (PAHs) are known to be toxic, mutagenic and/or carcinogenic, and their contamination of soils and aquifer is of great environmental concern. Laccases (E.C. 1.10.3.2) are phenoloxidases that catalyze the oxidation of PAHs in the presence of mediator compounds that act as “electron shuttle” between the free enzyme and the substrate. However, the oxidative potential of immobilized laccase-mediator system for in vitro reaction with PAHs in contaminated waters has not been studied. Laccase from Trametes versicolor was immobilized on kaolinite, and its potential to oxidize anthracene and benzo[a]pyrene in a sole-substrate system in the presence of 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) was investigated. Results indicated that immobilization improved stability of laccase to temperature, pH, inhibitors and storage time compared with the free enzyme. The immobilized laccase-mediator system was as efficient as the free enzyme in oxidizing the PAHs tested. After 24 h of incubation, immobilized laccase–ABTS system oxidized more than 80% of the initial 70 μM of PAHs present. In the presence of ABTS, immobilized laccase oxidized PAHs on continuous basis with only a slight decrease in activity. In view of the pollution of soils, sediments and waste waters by PAHs, the results presented indicate a new opportunity for application of immobilized laccase in bioremediation.