Fungal laccase-polycarboxylate functionalized magnetic nanoparticles enable highly efficient degradation of tetracycline antibiotics in marine aquaculture wastewater

Residues of tetracycline antibiotics (TCs) in aquaculture pose serious risks to environmental and human health. Although laccase-based enzymatic degradation offers a green and sustainable strategy for removing TCs from marine aquaculture wastewater, its application is often hindered by inefficient enzyme production and stability issues. In this study, we engineered Aspergillus oryzae , a Generally Recognized as Safe (GRAS) filamentous fungus with powerful secretory capabilities, for the homologous overexpression of laccase. After purification, the laccase was stably immobilized onto polycarboxylate-functionalized magnetic nanoparticles via covalent bonding. Compared with free laccase, the immobilized enzyme exhibited markedly enhanced performance under various conditions, including pH tolerance, thermostability, long-term storage stability, and reusability. This novel biocatalyst, exhibiting optimal activity under neutral to slightly alkaline conditions, was subsequently applied to degrade TCs in simulated aquaculture wastewater. The maximum removal efficiencies of tetracycline (TC) and oxytetracycline (OTC) (10 mg/L) by the immobilized laccase reached 82.9% and 87.84%, respectively. Based on the identification of intermediates, the pathways for TC removal involve dehydrogenation, demethylation, and ring-opening reactions, resulting in less toxic and readily biodegradable products. Overall, this system demonstrates strong potential for effective removal of TCs from aquaculture wastewater and for broader environmental remediation applications.