Advanced Water Management Centre, The University of Queensland, St. Lucia, Brisbane, QLD, 4072, Australia.
School of Civil and Environmental Engineering, University of Technology Sydney, Ultimo, NSW, 2007, Australia.
Water Res. 2020 Apr 15;173:115592. doi: 10.1016/j.watres.2020.115592. Epub 2020 Feb 5.
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.
污水处理厂（WWTP）已被确定为抗生素的储存库之一。尽管硝化细菌已被报道能够降解各种抗生素，但很少有研究调查抗生素对硝化细菌的动力学和微生物响应的长期影响。在这项研究中，头孢氨苄（CFX）和磺胺嘧啶（SDZ）被选择用于评估两种独立生物反应器中浓度逐渐增加的硝化污泥的慢性影响。结果表明，CFX 和 SDZ 在初始浓度为 100μg/L 时可被富集硝化污泥有效去除，去除效率分别超过 88%和 85%。与异养菌和亚硝酸盐氧化菌的有限贡献相比，氨氧化菌（AOB）通过共代谢对 CFX 和 SDZ 的生物降解做出了主要贡献。与对照阶段（无 CFX 或 SDZ）相比，慢性暴露于 CFX（≥30μg/L）可刺激氨氧化活性，显著提高氨氧化速率（p<0.01）。相比之下，由于暴露于 30μg/L SDZ 而抑制了氨氧化活性（p<0.01），然后在暴露于 50 和 100μg/L SDZ 下长期适应后恢复。此外，16S rRNA 基因扩增子测序显示，在对照阶段（无 CFX 或 SDZ），AOB 的相对丰度从 23.8%下降至 14.2%和 10.8%，而在暴露于 100μg/L CFX 和 SDZ 时分别下降至 28.8%和 10.8%。然而，amoA 基因的表达水平上调以克服这种不利影响，并保持对铵和抗生素的稳定和高效去除。本研究结果阐明了抗生素暴露对 WWTP 中富集硝化污泥动力学和微生物响应的慢性影响。
