BACKGROUND: Effluents from the dyeing process containing dyes are difficult to degrade biologically. Therefore enzymatic dye decolorisation has received considerable attention recently. In this study the dye decolorisation potential of crude laccase from the white rot fungus Rigidoporus lignosus W1 was demonstrated on an anthraquinone dye, Remazol Brilliant Blue R (RBBR), and a triphenylmethane dye, malachite green (MG). Effects of pH, temperature and ionic strength on laccase activity and decolorisation efficiency were investigated. RESULTS: Native polyacrylamide gel electrophoresis (PAGE) and sodium dodecyl sulfate PAGE confirmed the decolorisation ability of the crude enzyme on RBBR and MG. A single laccase with a molecular mass of about 40 kDa appeared to be involved in the process. Efficient enzymatic decolorisation without redox mediator was achieved, with 39 mg L-1 MG being removed within 2 h and 160 mg L-1 RBBR within 1 h at 60 degrees C and pH 4.5. Although the laccase activity was inhibited in the presence of NaCl, it was renatured gradually in low concentrations of NaCl (<0.8 mol L-1), resulting in unusual dye decolorisation kinetics. Surprisingly, unusual storage stability at alkaline pH was observed, with the laccase activity being enhanced 1.5-2-fold after 3 h of incubation. CONCLUSION: Crude laccase with unusual storage stability from the fungus R. lignosus W1 showed excellent decolorisation ability on RBBR and MG without redox mediator. This laccase would seem to be a good candidate for application in dye decolorisation and textile effluent biotreatment. (C) 2008 Society of Chemical Industry