Comparative detoxification of Remazol Rrilliant Blue R by free and immobilized laccase of Oudemansiella canarii

A laccase from Oudemansiella canarii was immobilized using the crosslinked enzyme aggregate (CLEA) methodology and applied in the degradation of the anthraquinonic dye Remazol Brilliant Blue R (RBBR). The immobilized laccase was superior to the free laccase in both thermal and storage stabilities. Both immobilized and free laccase decolourized 100mg/L RBBR within 24 h at 30 degrees C and pH 5.0, but the former was still efficient in degrading the dye after at least 6 cycles. The relationship between the decolorization rate and the RBBR concentration obeyed Michaelis-Menten kinetics, with KM of 0.126 +/- 0.044mmol/L and Vmax of 1.412 +/- 0.295 mmol/min for free laccase and KM of 0.159 +/- 0.050mmol/L and Vmax of 1.214 +/- 0.242 mmol/min for immobilized laccase. Fourier transform infra-red spectroscopy (FTIR) and mass spectrometry allowed to conclude that the O. canarii laccase acts not only on the chromophore group of the dye, but that it also cleaves other covalent bonds, causing an effective fragmentation of the molecule. The Microtox assay detected a significant diminution in toxicity, a finding corroborated by the phytotoxicity test performed with lettuce seeds. Our results indicate that the immobilized laccase from O. canarii could be useful in biological strategies aiming at degrading unwanted dyes in the environment.