Plastiome in seagrass meadows: higher health risk of plastisphere beneath leaf canopy than that in root sediment.

Microplastics (MPs) act as vectors for disseminating antibiotic resistance genes (ARGs) across ecosystems, posing potential threats to environmental and public health. Seagrass meadows serve as vital ecotones between land and sea, where MPs pollution is widely recognized. However, plastisphere resistome (plastiome) in this ecosystem and its modulation by native phyllosphere and rhizosphere microbiomes remain poorly understood. Herein, MPs were in-situ exposed to seagrass meadows to investigate differences in resistome profiles of phyllosphere-associated (SL-MPs) vs. rhizosphere-associated plastisphere (SR-MPs). The potential health risk was evaluated by profiling ARGs, virulence factor genes (VFGs)-associated pathogenicity and mobile genetic elements (MGEs)-mediated motility. Results showed that SL‑MPs harbored more abundant putative pathogens, ARGs and VFGs than SR-MPs. Specifically, SL-MPs were dominated by WHO critical-priority pathogens Pseudomonas aeruginosa and Klebsiella pneumoniae, and enriched ARGs conferring multidrug resistance. Additionally, SL‑MPs exhibited greater potential health risks and more abundant high-risk ARGs (e.g., bacA and floR). These traits appeared to be primarily associated with the dense biofilms, high cell motility, pronounced reactive oxygen species response, DNA recombination and distinct membrane features of plastisphere beneath leaf canopy. Since phyllosphere-associated plastisphere can be readily dispersed by waves to other coastal ecosystems, it is necessary to integrate ecological connectivity into "One Health" frameworks.