Decolorization of Bromophenol Blue by Free and Immobilized Crude Extracellular Laccase Preparation from Bjerkandera adusta TMF1 Produced on Agro-Industrial Residues

Abstract

Abstract

Synthetic dyes released from industrial effluents represent an important environmental challenge due to their persistence and toxicity. In this study, for the first time, a crude extracellular laccase preparation from Bjerkandera adusta TMF1 produced by solid-state fermentation on a wheat/barley bran mixture was immobilized onto glutaraldehyde-activated alginate beads and applied for mediator-free Bromophenol Blue (BPB) decolorization. The produced laccase showed high activity (51.51 IU/mL; 128.77 IU/g dry substrate), while immobilization efficiency reached 98.84% with 88.39% residual activity under optimal immobilization conditions. FTIR and SEM analyses indicated successful enzyme immobilization and structural changes in the alginate matrix. Under optimal conditions (50 mg/L BPB, pH 5, 30 °C), free and immobilized crude extracellular laccase preparation achieved 73.02% and 78.12% decolorization within 1 h, respectively, without the addition of synthetic redox mediators. The immobilized preparation retained decolorization ability during repeated use, maintaining more than 50% decolorization efficiency after the third cycle. HPLC analysis indicated changes in the chromatographic profile of BPB after enzymatic treatment, while phytotoxicity and antimicrobial assays suggested reduced toxicity of the treated samples toward the tested organisms. These results demonstrate that a crude extracellular laccase preparation produced by B. adusta TMF1 can serve as an efficient immobilized biocatalyst for Bromophenol Blue decolorization while supporting the sustainable valorization of agro-industrial residues for low-cost enzyme production.