Deciphering the mechanisms shaping the plastisphere antibiotic resistome on riverine microplastics

Microplastics in urban rivers provide bacterial niches and serve as dispersal vectors for antibiotic resistant genes (ARGs) dissemination, which may exacerbate risks in the aquatic systems. However, whether MPs in the river would also selectively enrich ARGs and the underlying mechanisms shaping the resistome on MPs remains largely unknown. In this study, we explored the occurrence of ARGs, bacterial communities, and mobile genetic elements (MGEs) on MPs and in waters from the Huangpu River in China. Microplastics were widely distributed in the river (1.78 ± 0.84 items/L), with overwhelming percentages of polyethylene terephthalate fibers. Although reduced ARG abundances were observed on MPs than in waters, MPs selectively enriched the ARGs resistant to Rifamycin and Vancomycin. A clear variation for ARG profiles was elucidated between water and MPs samples. Network analysis suggested that MPs created a unique niche for the genus Afipia to colonize, potentially contributing to the vertical dissemination of ARGs. Additionally, the co-occurrence between ARGs and MGEs revealed that the MPs favor the propagation of some plasmid-associated ARGs mediated by horizontal gene transfer. The null model-based stochasticity ratio and the neutral community model suggested that the ARG assembly on MPs was dominantly driven by stochastic process. The results further indicated that microbial communities and MGEs played significant roles in shaping ARG profiles and dynamics on MPs. Our findings provided new insights into the ecological processes of antibiotic resistome of the aquatic plastisphere.