PURIFICATION AND BIOTECHNOLOGICAL APPLICATIONS OF LACCASE PRODUCED BY ASPERGILLUS NIGER UNDER SURFACE FERMENTATION TECHNIQUE

Abstract

This study focuses on the production, purification, and biotechnological applications of laccase enzyme synthesized by Aspergillus niger under surface fermentation conditions. Laccases are multi-copper oxidases with wide substrate specificity, enabling their use in diverse industries such as textiles, food processing, and environmental remediation. A locally isolated strain of A. niger was cultivated, and fermentation parameters were systematically optimized using the one-factor-at-a-time (OFAT) approach. Carbon and nitrogen sources, pH, temperature, incubation period, and metal ion supplementation were evaluated to enhance enzyme yield. Sucrose (4 g/100 mL) and yeast extract (5 g/100 mL) were identified as optimal nutritional sources, while pH 6.0, incubation at 30 °C, and a 7-day fermentation period yielded maximum extracellular activity (0.416 ± 0.016 U/mL). Copper (0.5 g/100 mL) acted as a strong inducer, whereas higher concentrations of zinc and iron salts inhibited production. Biochemical characterization revealed maximum activity at 37 °C and pH 5.5, confirming the enzyme’s moderate thermostability and acidic optimum. Partial purification by TLC and ammonium sulfate precipitation enriched enzymatic activity. The crude laccase displayed strong bioremediation potential: textile effluents were decolorized up to 50.78% after 10 days, while tannery wastewater exhibited rapid decolorization of 66.6% within 24 hours. These findings highlight the industrial significance of A. niger laccase as an eco-friendly biocatalyst and establish optimized conditions for its scalable production and application in wastewater treatment.