Microplastics selectively enrich potential plastic-degrading bacteria in estuaries

Being the transition zones between rivers and the ocean, estuaries are critical pathways for the transport of millions of tons of land-based microplastics (MPs) into the ocean. These dynamic systems facilitate significant transformation processes for MPs, particularly through their interactions with microbial communities. However, the dynamics of the Plastisphere, particularly how it varies across different types of estuaries and in response to seasonal environmental changes, remain poorly understood. To address this knowledge gap, comprehensive samples were collected from four major estuaries (Qiantangjiang, Jiaojiang, Oujiang, and Minjiang River Estuaries) in Southeast China during both spring and autumn. The diversity of microorganisms associated with water, sediment, MPs, and particulate organic matter (wood) surfaces was analyzed. Our results indicated that bacterial species on MPs varied across estuaries in spring but exhibited no significant variation in autumn. The bacterial diversity on MPs was significantly different from that in water or sediment samples, but exhibited a similar pattern to that on particulate organic matter, with dominant species being more abundant on MPs. Eukaryotic diversity on MPs closely mirrored that in water, although more specific fungal species were found in the water. Despite these similarities, bacteria on MP surfaces exhibited higher levels of xenobiotic biodegradation and metabolism compared to the other three matrices. Species classification and functional annotation revealed a higher proportion of potential plastic-degrading bacteria on MP surfaces, indicating that the enrichment of potential plastic-degrading bacteria on MPs was driven by their direct association with plastic degradation, rather than their planktonic state or surface attachment.