Biodegradation and detoxification of malachite green dye by extracellular laccase expressed from Fusarium oxysporum

The present study evaluated the potential of biodegrading the toxic synthetic dye malachite green (MG) by an enzymatic approach. Extracellular laccase derived a fungal strain Fusarium oxysporum HUIB02 was used in the direct biodegradation of MG. Time-course study showed that the crude laccase successfully removed ≥ 80% MG after 20 h of treatment. The presence of Cu²⁺ ions enhanced MG degradation, while cation Fe²⁺ and anions including Cl⁻ and I⁻ reduced the degradation efficiency. The optimal temperature was 40 °C. Supplementation of mediators including syringaldehyde (SA), 1-hydroxybenzotriazole (HBT), and vanillin (VA) improved the MG degradation up to 99%. Under the optimal reaction conditions, the MG degradation efficiency of laccase reached ≥ 90% when MG concentration was ≤ 100 mg/L. At a higher concentration (1000 mg/L of MG), the enzyme still removed 88.1% the present dye. The detoxification evaluation confirmed the nullification of MG toxicity on microorganism after the enzymatic treatment. Hence, this enzymatic degradation approach is promising for the treatment of effluents containing MG.