细胞外抗生素抗性基因(eARG)是污水处理厂(WWTP)中重要的新兴环境污染物。营养底物缺乏(即,饥饿)经常发生在污水处理厂,由于每年的维护,水质波动,和污泥储存;它可以极大地改变细菌的抗生素抗性和细胞外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仍然未知。在这里,我们使用宏基因组测序来探索饥饿情景的影响(碳,氮,和/或磷缺乏)和环境条件(厌氧-好氧交替,厌氧,缺氧,和有氧)在分布上,移动性,和活性污泥中的eARGs宿主。结果表明,30天的饥饿使eARGs的绝对丰度降低了40.9%-88.2%,但是高风险的双重和多重耐药基因仍然存在。饥饿,特别是同时缺乏碳,氮,和磷在有氧条件下,通过减少细胞外移动遗传元件(eMGEs)的丰度来有效缓解eARGs。饥饿还改变了eARGs细菌宿主的概况和细菌群落组成,后者通过改变eMGE对eARG产生间接的积极影响。我们的发现揭示了饥饿条件下活性污泥中eARGs的响应模式和机制,并强调了饥饿是减轻污水处理厂先前被忽视的eARGs风险的潜在策略。
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.