Plastisphere microbial succession and predicted functional responses: a 60-day temporal study in wastewater effluent

Abstract Although wastewater treatment plants (WWTPs) achieve high microplastic removal efficiency, substantial quantities are still discharged, and the long-term dynamics of plastisphere microorganisms on their surfaces and potential impacts on receiving waters remain poorly understood. Here, we conducted a 7-15-30-60-day in situ incubation of microbial communities on five polymers (PVC, PE, PP, PET, PLA) and two natural particles (sawdust, gravel) at a WWTP outfall, integrating absolute quantitative 16S rRNA amplicon sequencing, biofilm characterization, and multi-dimensional ecological analyses. Temporal water-quality variation showed stronger associations with community divergence than particle type, which showed subtler taxon-specific associations. Microplastic-associated communities resembled those on gravel but diverged from sawdust, which exhibited long-term selective microbial enrichment due to higher bioavailability. Dominant taxa governed overall traits (e.g., biofilm formation, diversity, stability, assembly), whereas specialized taxa underpinned specific functions. Although microbial communities initially stabilized by day 15, those associated with recalcitrant microplastics (PE, PP, and PET) continued to differentiate through day 60, suggesting that 30-day incubations may not accurately capture microplastic-associated microbial ecological risks in flowing waters. This study advances understanding of the long-term ecological behavior of microplastics as microbial vectors in natural waters and supports ecological risk assessment and management of microplastics in WWTP effluents.