Laccase inducer Mn2+ inhibited the intracellular degradation of norfloxacin by Phanerochaete chrysosporium

The effect of extracellular enzyme inducers such as Mn2+ on the intracellular degradation system of white-rot fungi is still unknown. In this study, the effect of Mn2+ on the degradation of norfloxacin (NOR) by Phanerochaete chrysosporium (P. chrysosporium) and its mechanisms were investigated. A higher concentration of Mn2+ led to higher adsorption of NOR but weaker degradation of NOR and, ultimately, lower removal efficiency of NOR by P. chrysosporium. The addition of Mn2+ increased the activities of both laccase (Lac) and manganese peroxidase (MnP), but only Lac played a role in the degradation of NOR, indicating that Mn2+ probably induced a greater contribution of extracellular Lac to NOR degradation by P. chrysosporium. Further investigation demonstrated that Mn2+ displayed a similar inhibitory effect on NOR degradation as the cytochrome P-450 inhibitor 1-aminobenzotriazole (ABT). Mn2+ inhibited the oxidation of the piperazine ring of NOR by P. chrysosporium, which resulted in similar changes in degradation products to those in the ABT-added group. These findings demonstrated that Mn2+ inhibited the intracellular degradation of NOR by cytochrome P-450. [Display omitted] •Mn2+ induced higher Lac activity, but inhibited the overall biodegradation of NOR.•The degradation pathways of NOR were proposed.•Mn2+ inhibited the oxidation of piperazine substituents in NOR.•Mn2+ inhibited the conversion of N2 to N3 and the early accumulation of N4 and N5.