Plastic materials, seasons and land use impact the microbial community composition in biofilms associated with microplastics in urban freshwater environments

Microplastics (MPs) in freshwater systems have emerged as great threats to natural environments and public health, yet the microbial community of biofilms formed on MPs remains understudied. This study investigated the microbial communities in biofilms developed on different non-biodegradable and biodegradable MPs across seasons and land uses after a 60-day in-situ incubation using 16S rRNA gene sequencing to explore the microbial community structures and their relationships with environmental factors. Results revealed that biofilm communities exhibited significantly higher alpha diversity than surrounding water (Shannon, p < 0.001), dominated by the phylum Proteobacteria (up to 79.25% in relative abundance). Seasonal variations in microbial community structure were observed (PERMDISP: F = 32.6, p < 0.0001; W_d∗ test: p = 0.001), with Nitrospira more abundant in summer and autumn, while Nitrosomonas was found more in winter. Specifically, in summer and autumn, unique microbial community was found in biofilms formed on biodegradable MPs compared to non-biodegradable materials. Although the influences of land use patterns were limited (2.13% of unique variation) compared with seasonal variations (62.55%) and plastic materials (5.93%), distinct microbial communities were detected in areas dominated by commercial land use (COM). Notably, Nitrospira exhibited special responses to industrial land with municipal utilities (INDW) and COM, suggesting that surrounding environmental conditions may be associated with specific taxa within biofilms developed on MPs. Consequently, seasonal changes, plastic materials, and certain land use patterns were identified to impact the microbial community structures in the biofilm on MPs, indicating the impactful role of MPs in freshwater systems.