Catalytic behavior and detoxifying ability of an atypical homotrimeric laccase from the thermophilic strain Scytalidium thermophilum on selected azo and triarylmethane dyes

Laccase catalyzed decolorization and detoxification was investigated for the azo dye Congo Red and three triarylmethane dyes: Malachite Green, Bromo-Cresol Green and Phenol Red, commonly found in textile industry effluents. In the present work, we studied various physico-chemical parameters such as pH, temperature, ionic strength and initial dye concentration to achieve maximum dye decolorization by Scytalidium thermophilum laccase. The enzyme efficiently decolorized dyes from 46% to 99% at 50 mg/l of initial dye concentration in the presence of 0.1 U/ml of laccase. Under optimized conditions, Km values of the enzyme were 0.25; 3.31; 5.61 and 172.1 mM toward Phenol Red, Congo Red, Malachite Green and Bromo-Cresol Green, respectively. Among these four dyes, Bromo-Cresol Green at a concentration of 10,000 mg/l showed the best decolorization reaching 83% within 6 h. Cytotoxicity and microtoxicity evaluation demonstrated a decreased toxicity of the final degraded products.