Purification and characterization of the laccase produced by the Lysinibacillus boronitolerans and its role in the decolourization of synthetic dyes.

Synthetic dyes released by the textile industry pose a significant environmental concern due to their complex structure, persistence, and hazardous effects on ecosystems and human health. In this study, laccase enzyme produced by Lysinibacillus boronitolerans was isolated, characterized, and tested for its capacity to break down synthetic dyes. The extracellular enzyme was purified using ammonium sulphate precipitation, dialysis, and Sephadex-75 gel filtration chromatography, yielding a 12.19-fold purification with a recovery rate of 63.86%. SDS-PAGE analysis confirmed the enzyme's purity, revealing a single protein band with a molecular weight of approximately 45 kDa. The purified laccase demonstrated the highest activity at pH 5 and 40 °C while remaining rather stable throughout a moderate temperature range. Cu²⁺ ions significantly increased enzyme activity, while inhibitors, including sodium azide, inhibited it. Kinetic studies utilizing ABTS as a substrate revealed high substrate affinity (Km = 6.237 mM, Vmax = 0.795 µmol min⁻¹). The crude laccase successfully decolorized numerous textile dyes, with Congo red showing the greatest degradation (61%). Further optimization with Response Surface Methodology increased Congo red decolorization to 84.5% under ideal conditions. These findings highlight L. boronitolerans laccase's significant potential as an environmentally benign and efficient biocatalyst for the remediation of textile dye effluent.