Microplastics in Motion: How Earthworm Guts Become Microbial Gateways through Plastic Surface Dynamics

Microplastics (MPs) pollution in terrestrial ecosystems poses significant ecological risks, particularly as carriers of microbial communities and potential pathogens. However, the mechanisms by which MPs interact with microbes during transit through soil animal digestive systems remain poorly understood. This study investigated the interactions between poly(ethylene terephthalate) (PET) and polystyrene (PS) MPs and gut-derived microbes using a biomimetic earthworm gut model. PET and PS MPs exhibited distinct microbial colonization patterns, driven by their physicochemical properties. PET MPs, with rougher surfaces, preferentially adsorbed cocci such as Paraclostridium, fostering high-density but low-activity bacterial populations. Conversely, PS MPs, with smoother surfaces, enriched bacilli such as Raoultella, supporting low-density but high-activity bacterial communities. PET MPs facilitated rapid bacterial proliferation but lacked long-term stability, whereas PS MPs created persistent microenvironments that increased the ecological risk of pathogen retention and spread. The oxidative degradation of MPs during gut transit enhanced bacterial adhesion by forming reactive surface functionalities. MPs significantly altered microbial diversity and served as selective vectors for microbial dissemination into soil ecosystems, disrupting the microbial dynamics. These findings underscore the dual role of MPs as microbial scaffolds and ecological disruptors, providing critical insights into their ecological impacts and guiding strategies to mitigate MP contamination and pathogenic risks.