摘要

抗生素的应用与命运与人类健康和生态平衡密切相关，逐渐引起了全球的广泛关注。长期抗生素残留可在环境中容易诱导抗生素耐药和耐药基因（ARGs）。虽然许多研究都在实验室或控制条件下研究了土霉素（OTC）的生物合成或降解代谢途径及其影响因素，但对OTC降解途径及环境影响因素的了解还很差。本研究研究研究了不同碳源、金属离子、底物浓度、温度、pH值以及相对丰度随时间变化而变化的假单胞菌（T4）在OTC生物降解中的作用。结果表明，T4作为唯一碳源可降解OTC。与Cu2+相比，Fe3+的加入能显著促进T4的生长，并使OTC降解率提高到65.3%。OTC初始浓度、温度和pH值对OTC降解有显著影响。在初始OTC浓度为50 mg L−1时，在Fe3+存在下，T4降解OTC的百分比可达到81.0%，在40°C和pH＝7时，OTC降解率可达81.0%。本研究中，T4在OTC降解过程中未发现常见的四环素ARGs。用超高清晰度精密质量四极飞行时间串联质谱（QTOF/MS）对8种主要的OTC降解副产物进行了鉴定。提出了烯醇酮转化、羟基化、脱水、脱氨、脱甲基和脱羰基六种不同的反应类型和7种可能的降解途径。在最佳条件下，T4对池塘水、鱼废水和工业废水的OTC降解率分别达到88.2%、91.6%和92.0%。结果表明，T4在Fe3+存在下对水环境中OTC的生物降解有很高的促进作用，但不导致ARGs的发生。这对本研究提出的去除水生环境OTC具有重要意义。

The application and fate of antibiotics are closely related to human health and the ecological balance, which has gradually aroused the widespread global concerns. Long-term antibiotic residues can easily induce antibiotic resistance and antibiotic resistance genes (ARGs) in the environment. Although many studies have investigated the metabolic pathways of biosynthesis or degradation of oxytetracycline (OTC) and its influencing factors under laboratory or controlled conditions, the understanding of OTC degradation pathways and influencing factors in the environment is still poor. In the present study, the role of Pseudomonas (T4) in OTC biodegradation were investigated with different carbon sources, metal ions, substrate concentrations, temperatures, and pH values, as well as the temporal changes in the relative abundance of OTC ARGs. It was found that OTC could be degraded by T4 as a sole carbon source. Comparison with Cu2+, the addition of Fe3+ could significantly promote the growth of T4, and then increased the OTC degradation percentage to 65.3%. The initial concentration of OTC, temperature, and pH had significant impacts on OTC degradation. At the initial OTC concentration of 50 mg L−1, the percentage degradation of OTC by T4 could reach 81.0% at the presence of Fe3+, and at 40 °C and pH = 7. Common tetracycline ARGs were not found during the OTC degradation by T4 in the present study. The eight main putative OTC degradation byproducts were identified by ultra-high definition accurate-mass quadrupole time-of-flight tandem mass spectrometry (QTOF/MS). Six different reaction types and seven possible degradation pathways were proposed, including enol-ketone conversion, hydroxylation, dehydration, deamination, demethylation and decarbonylation. Under optimal conditions, the OTC degradation percentages by T4 could reach to 88.2%, 91.6% and 92.0% in pond water, fish wastewater and industrial wastewater, respectively. These results demonstrate the high effectiveness of T4 at the presence of Fe3+ for the enhanced biodegradation of OTC in water environment, without resulting in the occurrence of ARGs. This has important implications for the removal of OTC from aquatic environments by the technology proposed from this study.