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Polyvinyl chloride microplastic triggers bidirectional transmission of antibiotic resistance genes in soil-earthworm systems
Summary
This study found that PVC microplastics in soil trigger a two-way spread of antibiotic resistance genes between earthworm guts and the surrounding soil. The microplastics increased both the diversity and abundance of these resistance genes, with the transfer happening through bacteria sharing genetic material. This is concerning because earthworms are essential for soil health, and microplastics may be turning soil ecosystems into breeding grounds for antibiotic-resistant bacteria.
The diffusion and distribution of ubiquitous microplastics and antibiotic resistance genes (ARGs) in soil ecosystems are easily influenced by earthworm activity. However, minimal research exists on the bidirectional dissemination of ARGs in the soil-earthworm ecosystems under microplastic stress. Focusing on the typical microplastic polyvinyl chloride (PVC) microspheres in simulated soil-earthworm (Eisenia fetida) systems, we characterized the PVC-triggered interactive transmission of ARGs between earthworm guts and their dwelling soils using shotgun metagenomics and qPCR methodologies. PVC exposure did not alter the diversity and relative abundance of ARGs in earthworm-uninoculated soils but significantly increased those in earthworm-inoculated soils. Meanwhile, the abundance of ARGs increased in the earthworm gut under PVC stress. Source tracking analysis showed a higher source proportion of soil-borne ARGs into earthworm gut under PVC treatments. Mechanistically, PVC-triggered increasing prevalence of ARGs was significantly related to both the bacterial community and mobile genetic elements-mediated horizontal transfer in the soils, whereas the bacterial community predominated the process in the earthworm guts. Overall, our findings reveal a PVC-triggered bidirectional transmission pattern of ARGs between earthworm guts and their dwelling soils and highlight the overlooked ecotoxicological risk of microplastics in soil-earthworm systems.