The decolourization and detoxification of the triarylmethane dye Malachite green (MG) by laccase from Trametes sp. were investigated. The laccase decolorized efficiently the dye down to 97% of 50 mg L-1 initial concentration of MG when only 0.1 U mL(-1) of laccase was used in the reaction mixture. The effects of different physicochemical parameters were tested and optimal decolourization rates occurred at pH 6 and at temperatures between 50 and 60 degrees C. Decolourization of MG occurred in the presence of metal ions which could be found in textile industry effluent. 1-hydroxybenzotriazole (HBT) affected positively the decolourization of MG. The presence of some phenolic compounds namely ferulic, coumaric, gallic, and tannic acids was found to be inhibiting for the decolourization at a concentration of 10 mM.
The effect of laccase inhibitors in the decolourization of MG was tested with L-cysteine, and ethylene diamine tetra-acetic acid (EDTA) at concentrations of 0.1, 1 and 10 mM. It was demonstrated that L-cysteine and EDTA inhibited the decolourization starting from 1 mM concentration. However, for NaCl a concentration of 100 mM was needed for the inhibition of laccase. The decolourization of MG resulted in the removal of its toxicity against Phanerochaete chrysosporium.
The stability of the laccase toward temperature and HBT free radicals was also assessed during MG decolourization. It was shown that laccase was stable at 50 degrees C but in the presence of the laccase mediator HBT, the stability of the enzyme was severely affected resulting in a loss of 50% of the activity after 3 h incubation. (C) 2009 Elsevier Ltd. All rights reserved.
- malachite green
- white-rot fungi
- textile dyes