Effects of Nutrient Level and Growth Rate on the Conjugation Process That Transfers Mobile Antibiotic Resistance Genes in Continuous Cultures
Effects of Nutrient Level and Growth Rate on the Conjugation Process That Transfers Mobile Antibiotic Resistance Genes in Continuous Cultures
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DOI：
10.1128/aem.01121-22
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发表时间：
2022-09
影响因子：
4.4
通讯作者：
Mohammadreza Shafieifini;Yuepeng Sun;Zachery R. Staley;Jean‐Jack Riethoven;Xu Li
中科院分区：
文献类型：
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作者：
Mohammadreza Shafieifini;Yuepeng Sun;Zachery R. Staley;Jean‐Jack Riethoven;Xu Li
污水处理厂已被视为ARG的一个重要热点。污水处理厂出水的排放点是人类主导的生态系统与自然环境之间的重要界面，在此，ARGs可以从处理废水的细菌水平转移到接收水的细菌。摘要污水处理厂（WWTPs）出水中的细菌可以通过接合将抗生素抗性基因（ARGs）转移到受纳水中的细菌中，然而，在连续培养中缺乏对这种现象的定量评估。我们的目的是确定河流水体中的背景营养水平和细菌的生长速率对从流出物细菌到河流细菌的ARG接合频率以及对所得抗性水平（即，河水中的细菌。恒化器被用来模拟污水处理厂排入河流的排放点，在那里，流出物细菌（供体细胞）与河流细菌（受体细胞）相遇。供体细胞和受体细胞均为大肠杆菌细胞，供体细胞通过与当地污水处理厂出水中的细菌过滤交配而构建。结果表明，较高的细菌生长速率（0.45 h−1对0.15 h−1）导致较高的接合频率（每个受体10−4对10−6个接合子）。营养水平也显着影响接合频率，虽然在较小程度上比生长速率。对四环素的MIC从受体的2 mg/L增加到接合子的64 ~ 128 mg/L。相比之下，在突变体中MIC仅增加至高达8 mg/L。全基因组测序结果表明，在供体和接合子细胞中的tet质粒也存在于其他粪便细菌属中。从这项研究中获得的定量信息可以为与地表水中与废水相关的汞化合物扩散有关的危险识别提供信息。重要性污水处理厂已被视为ARG的一个重要热点。污水处理厂出水的排放点是人类主导的生态系统与自然环境之间的重要界面，在此，ARGs可以从处理废水的细菌水平转移到接收水的细菌。在以前的研究中使用的分批培养不能充分模拟营养条件和生长速度在接收水。在这项研究中，恒化器被用来模拟细菌在受纳水中的连续生长。此外，实验设置允许对营养水平的影响进行单独的研究（即，模拟河水中的背景营养物）和细菌生长速率对接合频率和产生的抗性水平的影响。该研究产生了统计上合理的生态数据，可用于估计作为“一个健康”框架一部分的废水来源的ARG的风险。
WWTPs have been regarded as an important hot spot of ARGs. The discharge point of WWTP effluent, where ARGs may be horizontally transferred from bacteria of treated wastewater to bacteria of receiving water, is an important interface between the human-dominated ecosystem and the natural environment. ABSTRACT Bacteria in the effluent of wastewater treatment plants (WWTPs) can transfer antibiotic resistance genes (ARGs) to the bacteria in receiving water through conjugation; however, there is a lack of quantitative assessment of this phenomenon in continuous cultures. Our objective was to determine the effects of background nutrient levels in river water column and growth rates of bacteria on the conjugation frequency of ARGs from effluent bacteria to river bacteria, as well as on the resulting resistance level (i.e., MICs) of the river bacteria. Chemostats were employed to simulate the discharge points of WWTPs into rivers, where effluent bacteria (donor cells) meet river bacteria (recipient cells). Both donor and recipient cells were Escherichia coli cells, and the donor cells were constructed by filter mating with bacteria in the effluent of a local WWTP. Results showed that higher bacterial growth rate (0.45 h−1 versus 0.15 h−1) led to higher conjugation frequencies (10−4 versus 10−6 transconjugant per recipient). The nutrient level also significantly affected the conjugation frequency, albeit to a lesser extent than the growth rate. The MIC against tetracycline increased from 2 mg/L in the recipient to 64 to 128 mg/L in transconjugants. In comparison, the MIC only increased to as high as 8 mg/L in mutants. Whole-genome sequencing showed that the tet-containing plasmid in both the donor and the transconjugant cells also occur in other fecal bacterial genera. The quantitative information obtained from this study can inform hazard identification related to the proliferation of wastewater-associated ARGs in surface water. IMPORTANCE WWTPs have been regarded as an important hot spot of ARGs. The discharge point of WWTP effluent, where ARGs may be horizontally transferred from bacteria of treated wastewater to bacteria of receiving water, is an important interface between the human-dominated ecosystem and the natural environment. The use of batch cultures in previous studies cannot adequately simulate the nutrient conditions and growth rates in receiving water. In this study, chemostats were employed to simulate the continuous growth of bacteria in receiving water. Furthermore, the experimental setup allowed for separate investigations on the effects of nutrient levels (i.e., simulating background nutrients in river water) and bacterial growth rates on conjugation frequencies and resulting resistance levels. The study generates statistically sound ecological data that can be used to estimate the risk of wastewater-originated ARGs as part of the One Health framework.