Revealing the anaerobic biodegradation pathway and mechanism of sulfamethoxazole by a novel Cupidesulfovibrio sp. strain SA-9

The widespread use of sulfamethoxazole (SMX) has raised significant concerns regarding environmental residue pollution and the emergence of bacterial antibiotic resistance. Anaerobes play crucial roles in the biogeochemical element cycle and the degradation of organic pollutants; however, the pure-cultured anaerobes involved in SMX anaerobic degradation and their underlying mechanisms remain largely unknown. In this study, a novel anaerobic bacterium, Cupidesulfovibrio sp. strain SA-9, was isolated and characterized for its ability to degrade SMX. Strain SA-9 preferentially utilized lactate or pyruvate as electron donors and sulfate, nitrate, or carbonate as electron acceptors to drive SMX degradation. The degradation T 1/2 values of SMX at concentrations ranging from 10 to 800 μM were between 6.0 and 17.2 d under optimal conditions which included pH 7.0-8.0, 30–37°C, sulfate as the electron acceptor, and pyruvate as the electron donor. Strain SA-9 degraded SMX via isoxazole ring cleavage, acetylation, and hydroxylation, and the ECOSAR-predicted results and bacterial growth inhibition assays indicated that these pathways was detoxifying. Multi-omics analysis and heterologous expression revealed that strain SA-9 degraded SMX via a reductive transformation pathway fueled by electron donors oxidized through the TCA cycle, with electrons transferred through a chain involving flavin-dependent thymidylate synthase (FDTS) and ferredoxin (Fd) to reduce electron acceptors that provide reducing power for SMX degradation. Furthermore, the degradation half-life ( T 1/2 ) values of SMX at 10 and 50 μM were 1.7 and 1.8 d in actual wastewater. Strain SA-9 significantly enhanced SMX removal and mitigated the dissemination risk of ARGs sul1 and sul2 in actual wastewater. This study elucidates the anaerobic microbial resistance mechanism to SMX and highlights the potential of strain SA-9 for the bioremediation of SMX-contaminated water.