Physiological characterization of anaerobic cometabolic transformation of sulfamethoxazole by Nitratidesulfovibrio vulgaris Hildenborough

Sulfonamide antibiotics are widely used in medicine and farming and residual amounts end up in wastewater effluents and solids applied as fertilizers in agriculture. Residues could promote antibiotic resistance propagation, especially during activated sludge treatment. We previously reported that Nitratidesulfovibrio vulgaris Hildenborough (NvH) (formerly Desulfovibrio vulgaris Hildenborough), can transform the sulfonamide antibiotic sulfamethoxazole (SMX) anaerobically. Here we studied the influence of SMX on the physiology of NvH, the effect of different electron donors on SMX transformation and the stability of the transformation products (TPs) under anoxic and oxic conditions. SMX transformation was catalyzed by resting cells and no difference was observed between acclimated and non-acclimated cells. Higher SMX transformation activity was observed with higher initial SMX concentrations and with younger cultures in exponential phase. SMX transformation was supported in the presence of lactate, and slowed down when lactate was depleted. When lactate was replaced with H ₂ plus acetate, sulfate reduction, cell growth, and SMX transformation still took place. The expression pattern of key catabolic proteins was unaltered by the presence of SMX. SMX was transformed by NvH to two major TPs, TP253 and TP255. TP255 was identified as the reduced form of SMX and was abiotically decaying under oxic conditions to TP187, which no longer had an intact sulfonamide structure. Our results suggest that SMX can be transformed under sulfate-reducing conditions by a sequence of anaerobic microbial reduction and oxic abiotic decay, decreasing the persistence and resistance propagation potential of SMX.