Application parameters of laccase–mediator systems for treatment of sulfonamide antibiotics

This is the first study to examine the application parameters for oxidation of two sulfonamide antibiotics (SAs), sulfadimethoxine (SDM) and sulfamonomethoxine (SMM), using a novel laccase and mediators. The optimal conditions in the laccase–mediator system (LMS) were pH 4, 50–60 °C, and 1 mM for 2,2′-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS); pH 4, 40–60 °C, and 1 mM for violuric acid (VLA); pH 6, 50 °C, and 2 mM for syringaldehyde (SIR). Additionally, the conditions of the 4-hydroxybenzyl alcohol (HBA) mediator were pH 4, 30 °C, and 2 mM in the oxidation of SDM; and the temperature increased to 60 °C for SMM. The laccase coupled with VLA and HBA resulted in the lowest toxicity of the SA solutions during processing, whereas treatments with ABTS and SIR resulted in higher toxicities. Furthermore, the laccase used in this study was stable and resistant to dialysis, thus can be reused for oxidation process.

► This study showed optimal conditions for laccase with mediators to oxidize SAs.
► Toxicities of SA solutions were lower in LMS with VLA and HBA than ABTS and SIR.
► The laccase was resistant to dialysis, and can be used repeatedly for oxidation process.
► VLA is a better mediator considering rates, pH, temperature, and concentration.