Microplastic aging drives convergence of the plastisphere microbiome and resistome toward agricultural soils.

Abstract

The degree of microplastic (MP) aging varies substantially in agricultural soils; however, how this common aging gradient influences the plastisphere microbiome and resistome remains largely unknown. We therefore collected polyethylene MPs from long‑term mulched farmlands and classified them into low‑aged plastispheres (LAPs) and high‑aged plastispheres (HAPs). Bacterial community dissimilarity to soil decreased progressively from LAPs to HAPs, accompanied by broadening niche breadth, increasing bacterial diversity, and a shift toward more stochastic community assembly. The diversity and abundance of antibiotic resistance genes (ARGs) declined significantly along the aging gradient, with clinically relevant high-risk ARGs (e.g., vanR, ugd, and aac(6')-I) decreasing by 53.34-84.01%. Furthermore, the ARG hosts shifted from Actinomycetota in LAPs to Pseudomonadota in soils. Variance partitioning showed that the carbonyl index uniquely explained 57.03% of the variation in plastisphere ARG profile distance toward soil, identifying MP aging as the primary driver of resistome convergence. Collectively, these findings demonstrate that natural MP aging drives a progressive convergence of the plastisphere resistome toward that of the surrounding soil, indicating that aged MPs may pose a reduced risk of antibiotic resistance compared to newly formed MPs. This convergence underscores the need to incorporate plastic aging into future risk assessment frameworks for plastisphere-associated ARGs.