Wastewater treatment plants (WWTPs) have been identified as one of the reservoirs of antibiotics. Although nitrifying bacteria have been reported to be capable of degrading various antibiotics, there are very few studies investigating long-term effects of antibiotics on kinetic and microbial responses of nitrifying bacteria. In this study, cephalexin (CFX) and sulfadiazine (SDZ) were selected to assess chronic impacts on nitrifying sludge with stepwise increasing concentrations in two independent bioreactors. The results showed that CFX and SDZ at an initial concentration of 100 μg/L could be efficiently removed by enriched nitrifying sludge, as evidenced by removal efficiencies of more than 88% and 85%, respectively. Ammonia-oxidizing bacteria (AOB) made a major contribution to the biodegradation of CFX and SDZ via cometabolism, compared to limited contributions from heterotrophic bacteria and nitrite-oxidizing bacteria. Chronic exposure to CFX (≥30 μg/L) could stimulate ammonium oxidation activity in terms of a significant enhancement of ammonium oxidation rate (p < 0.01). In contrast, the ammonium oxidation activity was inhibited due to exposure to 30 μg/L SDZ (p < 0.01), then it recovered after long-term adaption under exposure to 50 and 100 μg/L SDZ. In addition, 16S rRNA gene amplicon sequencing revealed that the relative abundance of AOB decreased distinctly from 23.8% to 28.8% in the control phase (without CFX or SDZ) to 14.2% and 10.8% under exposure to 100 μg/L CFX and SDZ, respectively. However, the expression level of amoA gene was up-regulated to overcome this adverse impact and maintain a stable and efficient removal of both ammonium and antibiotics. The findings in this study shed a light on chronic effects of antibiotic exposure on kinetic and microbial responses of enriched nitrifying sludge in WWTPs.

中文翻译：

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长期暴露于头孢氨苄和磺胺嘧啶的富集硝化污泥的动力学和微生物响应研究。

废水处理厂（WWTP）已被确定为抗生素的储存库之一。尽管据报道硝化细菌能够降解各种抗生素，但很少有研究研究抗生素对硝化细菌动力学和微生物反应的长期影响。在这项研究中，选择头孢氨苄（CFX）和磺胺嘧啶（SDZ）来评估在两个独立的生物反应器中浓度逐步升高对硝化污泥的慢性影响。结果表明，富集硝化污泥可有效去除初始浓度为100μg/ L的CFX和SDZ，去除效率分别超过88％和85％。氨氧化细菌（AOB）通过代谢作用对CFX和SDZ的生物降解做出了重大贡献，相比之下，异养细菌和亚硝酸盐氧化细菌的贡献有限。长期暴露于CFX（≥30μg/ L）会刺激铵的氧化活性，从而显着提高铵的氧化速率（p <0.01）。相反，由于暴露于30μg/ L SDZ，铵的氧化活性受到抑制（p <0.01），然后在暴露于50和100μg/ L SDZ下长期适应后恢复。此外，通过16S rRNA基因扩增子测序发现，暴露于100μg/ L CFX和SDZ时，AOB的相对丰度从对照期（无CFX或SDZ）的23.8％降至28.8％分别降至14.2％和10.8％，分别。然而，amoA基因的表达水平被上调，以克服这种不利影响，并保持稳定和有效地去除铵和抗生素。