Deciphering the pathogenic risks of microplastics as emerging particulate organic matter in aquatic ecosystem

Microplastics are accumulating rapidly in aquatic ecosystems, providing habitats for pathogens and vectors for antibiotic resistance genes (ARGs), potentially increasing pathogenic risks. However, few studies have considered microplastics as particulate organic matter (POM) to elucidate their pathogenic risks and underlying mechanisms. Here, we performed microcosm experiments with microplastics and natural POM (leaves, algae, soil), thoroughly investigating their distinct effects on the community compositions, functional profiles, opportunistic pathogens, and ARGs in Particle-Associated (PA) and Free-Living (FL) bacterial communities. We found that both microplastics and leaves have comparable impacts on microbial community structures and functions, enriching opportunistic pathogens and ARGs, which may pose potential environmental risks. These effects are likely driven by their influences on water properties, including dissolved organic carbon, nitrate, DO, and pH. However, microplastics uniquely promoted pathogens as keystone species and further amplified their capacity as hosts for ARGs, potentially posing a higher pathogenic risk than natural POM. Our research also emphasized the importance of considering both PA and FL bacteria when assessing microplastic impacts, as they exhibited different responses. Overall, our study elucidates the role and underlying mechanism of microplastics as an emerging POM in intensifying pathogenic risks of aquatic ecosystems in comparison with conventional natural POM. The rapid accumulation of microplastics in aquatic ecosystems and its associated pathogenic risks are becoming increasingly concerning. However, there remains limited research treating microplastics as POM to explore their pathogenic risks and underlying mechanisms. Here, our study demonstrates that both microplastics and leaves, owing to their substantial organic carbon leaching, markedly enrich pathogens and ARGs. Distinctively, microplastics promote pathogens as keystone species within bacterial communities and act as reservoirs for ARGs, leading to higher pathogenic threats. This study contributes to our understanding of the realistic environmental hazards posed by microplastics and the underlying mechanisms driving these risks.