Efficient immobilization of highly stable Bacillus amyloliquefaciens spore laccase for biodecolorization of textile dyes in water

Abstract

Abstract Globally, millions of cubic meters of dye-contaminated wastewater are generated annually from the textile industry. Discharging the dye-contaminated wastewater into natural water streams is detrimental to the ecosystem and human health. Wastewater bioremediation is considered a practical solution for converting wastewater into value-added water for safe reuse especially in irrigation. The present study investigated the immobilization of highly stable spore laccase enzyme of Bacillus amyloliquefaciens A1 by entrapment and adsorption techniques. Based on the results, agarose gel was the most efficient support with 94% immobilization yield. Optimum temperature of immobilized enzyme was at 60 ℃ with complete thermal stability for 120 min. The maximum activity of immobilized enzyme was at pH 6–7 and retained 91% of its activity after 24 h incubation. It showed 100% storage stability after 8 weeks which was higher than that of un-immobilized enzyme (4 weeks). The enzyme activity was nearly stable after 8 consecutive cycles of reuse. Decolorization of 8 textile dyes was studied using the immobilized enzyme. Crystal violet, direct red 81 and acid black 24 were efficiently decolorized (94.5, 77.4, and 68.8%, respectively) within 24 h in the first cycle. Reusability of immobilized enzyme showed 74.6, 53.5, and 51.8% decolorization of the same dyes in the same order after the second cycle. Immobilized spore laccase-treated dye water was used to irrigate lentil seeds and showed germination index about 73% compared to 10.8% for untreated one indicating very low toxicity of the treated dye water.

Keywords

• Spore laccase
• Immobilization
• Dye decolorization
• Phytotoxicity