Biotransformation Process of Fluoroquinolones by the Ligninolytic Enzymes of Phanerochaete chrysosporium

The increasing presence of antibiotics such as fluoroquinolones in the environment, originating from hospital, agricultural, industrial, and domestic effluents, poses a major threat to ecosystems and public health. In this study, we investigated the potential of the secretome of the white-rot fungus Phanerochaete chrysosporium , which contains key oxidative enzymes such as lignin peroxidases and manganese peroxidases, to biotransform these antibiotics. Two fluoroquinolones were selected: levofloxacin, commonly used in human medicine, and danofloxacin, widely applied in veterinary practices. Both compounds were tested at concentrations ranging from 5 to 25 mg/L. To maximize efficiency, key physicochemical parameters were optimized, including H₂O₂ and MnSO₄ concentrations, enzymatic activity, and the addition of chelators and mediators. The residual antimicrobial activity of the biotransformed antibiotics was assessed according to EUCAST guidelines. Lignin peroxidases were identified as the most effective enzymes, achieving up to 100% biotransformation of both fluoroquinolones under optimal conditions: 0.3 mM H₂O₂, 10 U/mL enzymatic activity, and absence of MnSO₄. Moreover, the transformation products exhibited markedly lower toxicity than the parent compounds, as confirmed by a plant germination assay. The potential transformation pathways and resulting by-products were identified using LC–MS/MS analysis. These pathways involved dealkylation, hydroxylation, and oxidation (observed only for levofloxacin), yielding dealkylated, hydroxylated, and oxidized derivatives of the original fluoroquinolones.