Pomacea canaliculata alters the composition, diversity, function, and assembly of bacterial community in freshwater plastisphere, shifting it closer to gut microbiota

The freshwater plastisphere, a unique ecological habitat formed on plastic surfaces in aquatic environments, has garnered increasing attention. Recent studies have primarily focused on its formation, composition, and responses to abiotic factors. However, the influence of biotic factors on the plastisphere has received comparatively less attention, particularly regarding its fate after ingestion and excretion by aquatic animals. Here, we conducted a microcosm experiment to investigate the effects of invasive snail Pomacea canaliculata on plastispheres formed on conventional polyethylene (PE) and biodegradable polylactic acid (PLA) microplastics (MPs). In the absence of snails, significant differences were observed in the structure, composition, diversity, function, and assembly of bacterial communities between PE and PLA plastispheres. Notably, the PLA plastisphere was enriched with more human pathogens. We found that P. canaliculata could directly ingest MPs or employ a behavior termed "pedal surface collecting" (PSC) to capture PE MPs for feeding. The gut of each tested snail was found to contain approximately 80 PE MPs (1 mm) or 26 PLA MPs (1 mm). The presence of snails significantly altered the bacterial community structure, composition, and function in both PE and PLA plastispheres, reducing α-diversity, phylogenetic diversity, dispersal limitation, and microbial network complexity. Meanwhile, in both plastispheres, the proportion of bacteria carrying mobile genetic elements increased, while bacteria associated with biofilm formation, denitrification, and plastic degradation decreased. These findings provide evidence that the plastisphere can carry microorganisms transferred from the snail gut, and highlight the potential risks of MPs as carriers of human pathogens for transmission from gut-to-gut or gut-to-environment.