Evidence of selective enrichment of bacterial assemblages and antibiotic resistant genes by microplastics in urban rivers

The ubiquitous presence of microplastics in aquatic environments has recently drawn considerable attention due to their potential threat to the entire ecosystem. The colonization of bacterial communities on microplastics is an important ecological linkage for microplastics in aquatic ecosystems, which is yet poorly understood. In this study, microplastic particles were sampled in two urbanized rivers in Jiaxing, Zhejiang, China, and the differences between bacterial assemblages colonizing microplastics and planktonic bacteria were estimated. Results from high-throughput sequencing showed that the bacterial communities on microplastics were less rich and diverse compared to those from the freshwater samples, with a significantly distinct taxonomic composition. The predicted functional profiles also indicated significant differences between microplastic and water samples. The functions related to biofilm formation and human diseases were relatively higher for the bacterial communities on the microplastics. Network analyses suggested that microplastic bacterial communities possessed higher average path length, clustering coefficient, and modularity compared to those in water samples. Additionally, quantitative PCR results showed microplastics selectively enriched antibiotic resistant genes (ARGs), and a good-fit correlation between ARG profiles and bacterial community composition was observed. The relative abundances of integron-integrase gene classes 1 and 2 were greater on microplastics, potentially suggesting a higher level of horizontal gene transfer. Findings of this study suggested microplastics are a novel microbial niche and may serve as hotspots for microbial interaction, potentially increasing risks to freshwater ecosystems and human health.