Differential patterns of antibiotic resistance, virulence, and dissemination risks in floating and sedimented plastispheres.

The plastisphere, a unique ecological niche on plastic surfaces, enriches microbial antibiotic resistance genes (ARGs) and virulence factors (VFs), posing environmental and health risks. Although aquatic sediment is a major sink for plastic contaminants, the resistance, virulence and dissemination potentials of sedimented plastispheres remain poorly characterized compared to floating plastics. Through investigation of metagenomes from two sites in the Pearl River in China, one of the world's plastic pollution hotspots, we report that water plastisphere showed 2.4 and 3.6 times more ARG and VF genes than those in sediment plastisphere and surrounding environments, together with higher mobile genetic element (MGE) abundances and a denser ARG-VF co-occurrence network (5,879 vs. 2,874 edges; density 0.043 vs. 0.025), indicating enhanced horizontal gene transfer potential. These differences coincide with contrasting ARG/VF assembly mechanisms, with deterministic and stochastic assembly processes dominating ARG/VF profiles in water and sediment plastispheres, respectively. Genome-resolved analyses further revealed that dominant plastisphere populations harbored multiple ARGs and VFs, with 41 MAGs predicted with pathogenicity capacities, most of which belonged to the families Mycobacteriaceae, Aeromonadaceae, Moraxellaceae, and Pseudomonadaceae. Notably, these taxa have been repeatedly reported as common plastisphere members across diverse ecosystems, suggesting that elevated resistance and virulence in floating plastispheres may be a widespread phenomenon across aquatic ecosystems. Together, our findings demonstrate that floating plastics act as dynamic vectors of antimicrobial resistance and pathogenicity, as well as their dissemination potentials, highlighting water-sediment transition may reduce these ecological risks within the plastisphere.