Decolorization of synthetic dyes by free and immobilized laccases from newly isolated strain Brevibacterium halotolerans N11 (KY883983)

Extracellular laccase produced from a novel soil bacterium Brevibacterium halotolerans N11 (KY883983) was purified with molecular weight of 55 kDa. Different carriers such as Ca-alginate, agarose-agar, agar-agar, alginate-gelatin mixed gel and polyacrylamide gel were utilized for laccase immobilization through this study. Kinetic properties of immobilized laccase showed that, Km value was slightly increased while Vmax was decreased compared to free counterpart. The optimum pH and temperature values were increased from 5 and 35 °C to 6 and 40 °C of free and immobilized laccases, respectively. Also, the thermal stability of immobilized laccase is more than the free one with Tm values of 58 °C and 26 °C, respectively. The immobilized laccase could be reused for seven continuous cycles with retained 65% of its initial activity. Thus, the immobilization process improved the enzyme thermal stability, reusability and reduced the enzyme cost. Due to synthetic dyes released to the environments and their low biodegradability, this study focused on the potential role of free and immobilized laccases as agents for biodegradation of synthetic dyes, especially: azo, triarylmethane and anthraquinone dyes under different conditions. Therefore, the biodegradation of different synthetic dyes by free and immobilized laccases was also studied. Both the free and the immobilized laccases exhibited high decolorization efficiency to congo red dye (50 mg L−1) at 40 °C for free enzyme and 50 °C for immobilized laccase after 24 h and pH 5.5. Our results confirm the role of B. halotolerans N11 laccase in dye decolorization and wastewater detoxification.