Antibiotics can be biodegraded in activated sludge via co-metabolism and metabolism. In this study, we investigated the biodegradation pathways of sulfamethoxazole (SMX) and antibiotic resistant genes’ (ARGs) fate in different autotrophic and heterotrophic microorganisms, by employing aerobic sludge, mixed sludge, and nitrifying sludge. A threshold concentration of SMX activating the degradation pathways in the initial stage of antibiotics degradation was found and proved in different activated sludge systems. Heterotrophic bacteria played an important role in SMX biodegradation. However, ammonia-oxidizing bacteria (AOB) had a faster metabolic rate, which was about 15 times higher than heterotrophic bacteria, contributing much to SMX removal via co-metabolism. As SMX concentration increases, the amoA gene and AOB relative abundance decreased in aerobic sludge due to the enrichment of functional heterotrophic bacteria, while it increased in nitrifying sludge. Microbial community analysis showed that functional bacteria which possess the capacity of SMX removal and antibiotic resistance were selected by SMX pressure. Potential ARGs hosts could increase their resistance to the biotoxicity of SMX and maintain system performance. These findings are of practical significance to guide antibiotic biodegradation and ARGs control in wastewater treatment plants.

抗生素可以在活性污泥中通过共代谢和新陈代谢进行生物降解。在本研究中，我们采用好氧污泥、混合污泥和硝化污泥研究了不同自养和异养微生物中磺胺甲恶唑 (SMX) 和抗生素抗性基因 (ARG) 的生物降解途径。在不同的活性污泥系统中发现并证明了在抗生素降解初期激活降解途径的 SMX 阈值浓度。异养细菌在 SMX 生物降解中发挥了重要作用。然而，氨氧化细菌 (AOB) 的代谢速度更快，比异养细菌高约 15 倍，这对通过共代谢去除 SMX 有很大贡献。随着 SMX 浓度的增加，amoA由于功能性异养细菌的富集，好氧污泥中基因和AOB相对丰度降低，而硝化污泥中AOB相对丰度增加。微生物群落分析表明，通过SMX压力筛选出具有SMX去除能力和抗生素耐药性的功能菌。潜在的 ARGs 宿主可以增加它们对 SMX 生物毒性的抵抗力并保持系统性能。这些发现对于指导废水处理厂抗生素生物降解和ARGs控制具有实际意义。