Hydraulic conditions control the abundance of antibiotic resistance genes and their potential host microorganisms in a frequently regulated river–lake system

Antibiotic resistance genes (ARGs) are a growing problem that is widespread in river–lake ecosystems, where they pose a threat to the aquatic environment's health and public safety. These systems serve as critical nodes in water management, as they facilitate the equitable allocation of water resources through long-term and frequent water diversions. However, hydrological disturbances associated with water-regulation practices can influence the dynamics of their potential host microorganisms and associated resistance genes. Consequently, identifying the key ARGs and their resistance mechanisms in heavily regulated waters is vital for safeguarding human health and that of river–lake ecosystems. In this study, we examined the impact of water-regulation factors on ARGs and their hosts within a river–lake continuum using 16S rRNA and metagenomic sequencing. We found that a significant increase in ARG abundance during regulation periods (p < 0.05), especially in the aquatic environment. Key resistance genes were macB, tetA, evgS, novA, and msbA, with increased efflux pinpointed as their principal resistance mechanism. Network analysis identified Flavobacteriales, Acinetobacter, Pseudomonas, Burkholderiaceae, and Erythrobacter as key potential host microorganisms, which showed increased abundance within the water column during regulation periods (p < 0.05). Flow velocity and water depth both drove the host microorganisms and critical ARGs. Our findings underscore the importance of monitoring and mitigating the antibiotic resistance risk during water transfers in river–lake systems, thereby supporting informed management and conservation strategies.