Pleurotus ostreatus and Lentinus sajor-caju laccases for sulfamethoxazole biotransformation: Enzymatic degradation, toxicity and cost analysis

Abstract

Sulfamethoxazole (SMX) is an antibiotic commonly used to treat human and animal infections. Therefore, it is one of the most identified pharmaceuticals worldwide in surface water and wastewater treatment plants. This work exploited Pleurotus ostreatus and Lentinus sajor-caju to produce laccase by using agricultural and food residues as substrates, specifically vine pruning and brewer's spent grains. The fungal laccases produced were then tested in the degradation of SMX in a water-based environment, both in the absence and presence of natural redox mediators. Both laccases with 0.5 mmol L−1 syringaldehyde (SYR) completely biotransformed SMX at 5 mg L−1 in <1 h using a low enzymatic concentration of 50 U L−1. Laccase from L. sajor-caju showed a higher capacity for SMX transformation, i.e., approximately 100 % of SMX degradation was attained in 30 min. The probable main metabolite was identified as the cross-coupling product resulting from the adductive reaction of 2,6-dimethoxy-1,4-benzoquinone phenoxy radical and the antibiotic SMX. The results of the comprehensive cost assessment suggest an economically feasible approach for the complete biotransformation of SMX from aquatic media using laccase. This manuscript presents a practical and efficient sustainable solution for addressing water pollution, offering a viable way to manage the issue.