An Extensive Assessment of Season Variations Induced by the Rainfall on Intracellular and Extracellular Args in the Urban River Replenished by Reclaimed Water

The health effect of antibiotic resistance genes (ARGs) remains to pose a major threat to the humans and environment, while little is known about the dynamic characteristics of different types of ARGs in the urban river systems, including intra- and extracellular ARGs (iARGs and eARGs). In this study, profiles of iARGs and eARGs and their associate MGEs were quantified using high-throughput quantitative PCR during dry and wet seasons in two typical reclaimed water replenishing urban rivers. Results showed that seasonal variations induced by rainfall significantly affect the absolute abundance and diversity of iARGs and eARGs (p < 0.01), in which absolute abundance of eDNA was approximately an order of magnitude greater than that of iDNA in the dry season. Conversely, rainfall demoted the diversity and absolute abundance of eARGs. Structural equation models (SEM) suggested MGEs, DOM, and pathogen were the predominant factor for eARG. Network analysis suggested tnp-04, tra-A, IS613, and tnpA-7 exhibited co-occurrence with eARGs in river and reservoir systems, regarded as molecular indicators to shape eARGs profiles. Given the findings that rainfall contributed the spread of eARGs, the risk triggered by DOM and pathogen in the river and reservoir system should be devoted more attention.