Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen, China.
University of Chinese Academy of Sciences, Beijing, China.
Appl Environ Microbiol. 2018 Apr 16;84(9). doi: 10.1128/AEM.02766-17. Print 2018 May 1.
The integron platform allows the acquisition, expression, and dissemination of antibiotic resistance genes within gene cassettes. Wastewater treatment plants (WWTPs) contain abundant resistance genes; however, knowledge about the impacts of wastewater treatment on integrons and their gene cassettes is limited. In this study, by using clone library analysis and high-throughput sequencing, we investigated the abundance of class 1, 2, and 3 integrons and their corresponding gene cassettes in three urban WWTPs. Our results showed that class 1 integrons were most abundant in WWTPs and that wastewater treatment significantly reduced the abundance of all integrons. The WWTP influents harbored the highest diversity of class 1 integron gene cassettes, whereas class 3 integron gene cassettes exhibited highest diversity in activated sludge. Most of the gene cassette arrays detected in class 1 integrons were novel. Aminoglycoside, beta-lactam, and trimethoprim resistance genes were highly prevalent in class 1 integron gene cassettes, while class 3 integrons mainly carried beta-lactam resistance gene cassettes. A core class 1 integron resistance gene cassette pool persisted during wastewater treatment, implying that these resistance genes could have high potential to spread into environments through WWTPs. These data provide new insights into the impact of wastewater treatment on integron pools and highlight the need for surveillance of resistance genes within both class 1 and 3 integrons. Wastewater treatment plants represent a significant sink and transport medium for antibiotic resistance bacteria and genes spreading into environments. Integrons are important genetic elements involved in the evolution of antibiotic resistance. To better understand the impact of wastewater treatment on integrons and their gene cassette contexts, we conducted clone library construction and high-throughput sequencing to analyze gene cassette contexts for class 1 and class 3 integrons during the wastewater treatment process. This study comprehensively profiled the distribution of integrons and their gene cassettes (especially class 3 integrons) in influents, activated sludge, and effluents of conventional municipal wastewater treatment plants. We further demonstrated that while wastewater treatment significantly reduced the abundance of integrons and the diversity of associated gene cassettes, a large fraction of integrons persisted in wastewater effluents and were consequentially discharged into downstream natural environments.
整合子平台允许在基因盒中获取、表达和传播抗生素耐药基因。废水处理厂 (WWTP) 中含有丰富的耐药基因；然而，关于废水处理对整合子及其基因盒的影响的知识有限。在这项研究中，我们通过克隆文库分析和高通量测序，研究了三种城市 WWTP 中 1 类、2 类和 3 类整合子及其相应基因盒的丰度。结果表明，WWTP 中 1 类整合子最为丰富，废水处理显著降低了所有整合子的丰度。WWTP 进水含有最高多样性的 1 类整合子基因盒，而 3 类整合子基因盒在活性污泥中表现出最高的多样性。在 1 类整合子中检测到的大多数基因盒阵列是新的。氨基糖苷类、β-内酰胺类和甲氧苄啶耐药基因在 1 类整合子基因盒中高度流行，而 3 类整合子主要携带β-内酰胺类耐药基因盒。在废水处理过程中，一个核心的 1 类整合子耐药基因盒库得以维持，这表明这些耐药基因有可能通过 WWTP 传播到环境中。这些数据为废水处理对整合子库的影响提供了新的见解，并强调需要监测 1 类和 3 类整合子中的耐药基因。废水处理厂是抗生素耐药细菌和基因传播到环境中的重要汇和运输介质。整合子是参与抗生素耐药性进化的重要遗传元件。为了更好地了解废水处理对整合子及其基因盒结构的影响，我们在废水处理过程中构建了克隆文库并进行了高通量测序，以分析 1 类和 3 类整合子的基因盒结构。本研究全面描述了常规城市废水处理厂进水、活性污泥和出水的整合子及其基因盒（尤其是 3 类整合子）的分布情况。我们进一步证明，尽管废水处理显著降低了整合子的丰度和相关基因盒的多样性，但很大一部分整合子在废水处理厂的出水中得以维持，并因此被排放到下游自然环境中。
