Enzymatic degradation and detoxification of azo dye Congo red by a new laccase from Oudemansiella canarii

A single laccase with molecular weight of 41 kDa was produced by the white-rot fungus Oudemansiella canarii cultured on solid state fermentation using a mixture of sugarcane bagasse-wheat bran as substrate. The enzyme (5 U) was able to decolourize 80% of 50 mg/L Congo red within 24 h at 30 degrees C and pH 5.5. The relationship between the decolorization rate and dye concentration obeyed Michaelis-Menten kinetics, with K-M and V-max values of 46.180 +/- 6.245 mu M and 1.840 +/- 0.101 mu mol/min, respectively. Fourier transform infrared spectroscopy (FTIR) and mass spectrometry allowed to conclude that the laccase acts not only on the dye chromophore group, but also that it cleaves different covalent bonds, causing an effective fragmentation of the molecule. The action of the laccase caused a significant reduction in toxicity, as indicated by the Microtox test. In conclusion, O. canarii laccase could be useful in future biological strategies aiming at degrading azo dyes.