Performance And Degradation Mechanism Of Sulfamethoxazole By Shewanella-Mediated Fenton-Like Reaction

Sulfamethoxazole(SMX)is a broad-spectrum antibiotic widely used in the treatment of various infectious diseases.However,due to its potential ecological threats,it has attracted extensive attention from government and environmental researchers.Currently,antibiotic treatment processes often rely on high-energy or potentially secondary-polluting physical and chemical removal methods.Recent studies have found that microorganisms can produce extracellular reactive oxygen species(ROS)under aerobic conditions to efficiently remove recalcitrant organic pollutants.However,the degradation performance of SMX in this process and the mechanisms of ROS production and defense under oxidative stress are still unclear.In this study,a Shewanella-mediated Fenton-like reaction was designed to catalyze the selfgeneration of extracellular ROS for the degradation of sulfamethoxazole.The results showed that this system can efficiently degrade sulfamethoxazole within 48 hours and operate efficiently for 15 cycles.Three possible degradation pathways for SMX degradation were inferred based on quantum chemical calculations and LC-MS/MS test results:benzene amino group removal,S-N bond cleavage,and acetylation.The sites of benzene amino group removal and S-N bond cleavage were found to be the same as the active sites attacked by hydroxyl radicals,indicating that they were results of free radical attack.The acetylation reaction began with the cleavage of the isoxazole ring and may be the result of biodegradation of SMX by S.O.MR-1 strain.ECOSAR toxicity analysis results showed that the toxicity of most intermediate products generated during the degradation process was significantly reduced compared to sulfamethoxazole,but the generation of benzene derivatives still needs attention.Genome annotation results showed that S.O.MR-1 contains a large number of genes related to the production of ROS and antioxidant stress response genes.Transcriptome sequencing results showed that the nadB gene encoding L-amino acid oxidase was significantly up-regulated in the biological Fenton group among genes related to ROS production,and the genes encoding NADH oxidoreductases were generally expressed in both the microbially driven Fenton group and Fe(III)-free control groups,indicating that the extracellular production of ROS by S.O.MR1 is the result of the joint action of NADH oxidoreductases and L-amino acid oxidase.KEGG enrichment analysis showed that S.O.MR-1 first secretes extracellular polymeric substances as the first line of defense to protect the cell membrane from oxidative damage by ROS,while using enzymatic antioxidants and non-enzymatic antioxidants to resist oxidative stress.The high extracellular ROS concentration also triggers the activation of ROS resistance mechanisms in S.O.MR-1.This study explored the degradation performance of microbe-driven Fenton-like reactions on SMX antibiotics,analyzed the mechanisms of extracellular ROS production and antioxidant stress response,and provided technical support and theoretical basis for the development of microbial-enhanced degradation processes for recalcitrant organic pollutants.