Antibiotic resistance genes (ARGs) are increasingly recognized as ubiquitous environmental contaminants in urban aquatic systems. In a new study published in Water & Ecology , a research team led by Hanxiao Zhang from Beijing Normal University analyzed 30 metagenomes from 15 sites across four waterbody types in Beijing—SNWDP-MR receiving waters, urban lakes, urban rivers, and suburban rivers—sampled in summer and autumn 2025.
The results revealed a habitat-associated signature. Urban rivers displayed the highest ARG burden, averaging 0.536 copies per cell and harboring the greatest subtype richness. Urban lakes exhibited the lowest burden at 0.199 copies per cell. Receiving waters occupied an intermediate position at 0.328 copies per cell; however, they showed the strongest ARG–mobile genetic element (MGE) coupling (R 2 = 0.965), indicating an elevated potential for horizontal gene transfer at these hydrological interfaces.
Notably, ARG abundance dropped significantly from summer to autumn (from 0.441 to 0.227 copies per cell), yet the spatial ranking among waterbody types remained stable. Statistical modeling demonstrated that ARG variation was jointly shaped by microbial composition, MGEs, and environmental factors (R 2 = 0.91~0.97), with MGEs serving as the strongest direct predictor in summer (path coefficient = 0.76).
Genomic binning further showed that the resistome was phylogenetically concentrated within Pseudomonadota, with Enterobacter identified as a core high-risk host harboring co-localized ARGs and virulence factors. The mobilome was dominated by transposase-related elements, particularly tnpA, suggesting that ARG mobility is primarily driven by a shared transposase-centered mechanism rather than by distinct plasmid-mediated processes across habitats.
“Our findings demonstrate that urban water networks act as connected yet selective resistome environments,” says Zhang. “The receiving waters represent a unique hydrological interface where resistance traits are actively reorganized. The strong ARG–MGE coupling signals that inter-basin water transfer may increase opportunities for resistance exchange, even when overall ARG abundance appears moderate.”
The study provides a framework for distinguishing between high-burden habitats and high-mobilization interfaces, offering a nuanced perspective for risk-oriented water management in megacities. The authors acknowledge limited site replication and the lack of metatranscriptomic validation, calling for future work with expanded sampling and integrated functional monitoring.
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Contact the author:
Hanxiao Zhang
School of Environment, Beijing Normal University, Beijing 100875, China
zhanghanxiao0912@126.com
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Water & Ecology
Observational study
Not applicable
Distribution, host association, and spread of antibiotic resistance genes in the water-receiving area of the Middle Route of the South-to-North Water Diversion Project
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.