Freshwater plastisphere structure and succession on diverse polymer surfaces: Linking plastisphere ecology and surface alterations in a 210-day field experiment

Freshwater plastic debris provides novel hard substrata that can alter the aquatic microbial ecosystem and community assembly, raising significant issues on how different materials influence microbial succession and the long-term ecology of plastisphere on biodegradable and compostable polymers. In this study, we conducted a 210-day in situ exposure experiment in a temperate lake to evaluate plastisphere development, microbial succession, physicochemical and microstructural surface modifications, as well as the occurrence of antimicrobial resistance genes (ARGs) on different biodegradable polymers. Biodegradable polymers, including bio-based PLA and PHBV, fossil-based PBAT, and their commercial compostable derivatives (starch blends and disposable plastic items), were compared to non-degradable polypropylene as a reference material. Microbial colonization patterns were assessed using high-throughput 16S rRNA gene sequencing and confocal laser scanning microscopy (CLSM) and microbial abundance and ARGs quantified via qPCR, while material changes were characterized by Fourier-transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and water contact angle measurements. All polymers and plastic surfaces were rapidly colonized, forming mature biofilms. Plastisphere succession was largely independent on polymer and plastic type, indicating a minor role of polymer chemistry in community structuring. Plastisphere development followed predictable ecological dynamics, with early colonizers occupying micro-niches and facilitating the establishment of structured, functionally diverse microbial communities primarily sustained by extracellular matrix and photosynthates. ARGs and potential opportunistic pathogenic genera occurred at low relative abundances, comparable to surrounding water. Overall, these results demonstrate that compostable and biodegradable polymers provide stable surfaces for microbial colonization in freshwater environments, offering mechanistic insight into microorganism-polymer interactions and highlighting plastisphere dynamics as a key factor shaping biofilm development and community structure.