摘要
      细胞外抗生素抗性基因（eARGs）是污水处理厂（WWTP）中新出现的重要环境污染物。由于每年的维护、水质波动和污泥储存，污水处理厂经常出现营养基质缺乏（即饥饿）；并且它可以极大地改变细菌的抗生素耐药性和细胞外DNA含量。然而，在饥饿胁迫下，活性污泥中eARGs的命运和相应的传播风险在很大程度上仍然未知。在此，我们使用宏基因组测序来探索饥饿情景（碳、氮和/或磷缺乏）和环境条件（厌氧-好氧、厌氧、缺氧和好氧交替）对活性污泥中eARGs的分布、迁移和宿主的影响。结果显示，30天的饥饿使eARGs的绝对丰度降低了40.9%-88.2%，但高风险的双耐药和多药耐药基因仍然存在。饥饿，特别是在有氧条件下同时缺乏碳、氮和磷，通过降低细胞外可移动遗传元素（eMGEs）的丰度，有效缓解了eARGs。饥饿还改变了eARGs的细菌宿主和细菌群落组成，后者通过改变eMGE对eARGs产生间接的积极影响。我们的研究结果揭示了饥饿条件下活性污泥中eARGs的反应模式和机制，并强调饥饿是减轻WWTP中先前被忽视的eARGs风险的一种潜在策略。
Abstract
Extracellular antibiotic resistance genes (eARGs) are important emerging environmental pollutants in wastewater treatment plants (WWTPs). Nutritional substrate deficiency (i.e., starvation) frequently occurs in WWTPs owing to annual maintenance, water quality fluctuation, and sludge storage; and it can greatly alter the antibiotic resistance and extracellular DNA content of bacteria. However, the fate and corresponding transmission risk of eARGs in activated sludge under starvation stress remain largely unknown. Herein, we used metagenomic sequencing to explore the effects of starvation scenarios (carbon, nitrogen, and/or phosphorus deficiency) and environmental conditions (alternating anaerobic-aerobic, anaerobic, anoxic, and aerobic) on the distribution, mobility, and hosts of eARGs in activated sludge. The results showed that 30 days of starvation reduced the absolute abundances of eARGs by 40.9%–88.2%, but high-risk dual and multidrug resistance genes persisted. Starvation, particularly the simultaneous lack of carbon, nitrogen, and phosphorus under aerobic conditions, effectively alleviated eARGs by reducing the abundance of extracellular mobile genetic elements (eMGEs). Starvation also altered the profile of bacterial hosts of eARGs and the bacterial community composition, the latter of which had an indirect positive effect on eARGs via changing eMGEs. Our findings shed light on the response patterns and mechanisms of eARGs in activated sludge under starvation conditions and highlight starvation as a potential strategy to mitigate the risk of previously neglected eARGs in WWTPs.

https://www.sciencedirect.com/science/article/abs/pii/S0043135423003895