Ecological Roles and Shared Microbes Differentiate the Plastisphere from Natural Particle-Associated Microbiomes in Urban Rivers

The "plastisphere," comprising microbes associated with microplastics (MPs), may have substantial ecological impacts on riverine ecosystems. However, little is known about how the microbiomes associated with anthropogenic MPs compare with those associated with natural particles (NPs) in urban rivers with varying MP pollution levels. We therefore conducted a comparative analysis of the metagenomes associated with MPs and NPs (100-5000 μm) and river water (RW) across 10 urban river systems. Although we found similarities in taxonomic and functional compositions between the microbiomes associated with MPs and NPs, the plastisphere exhibited distinct associations with specialized taxa and life-history strategies. These unique traits enhanced the potential of the plastisphere for complex carbohydrate and plastic degradation, nitrate and nitric oxide reduction, and antibiotic resistance and virulence compared with the NP or RW microbiomes. Furthermore, MPs supported the sharing of unique microbes with the surrounding RW; these shared microbes possessed enhanced horizontal gene transfer capabilities and potentially could disperse traits of the plastisphere into the broader RW microbiomes. This study highlights the distinct ecological roles and shared microbes of the plastisphere, indicating that MP pollution may substantially and uniquely impact the function and health of riverine ecosystems.