Opportunistic taxa promote the proliferation of antibiotic resistance genes in microplastic- and tetracycline-contaminated soils

Edaphic antibiotic resistance genes (ARGs) have garnered worldwide concern, yet mechanisms by which specific microbial taxa drive ARG variation under anthropogenic stress remain unclear. Here we show how opportunistic and sensitive taxa contribute to ARG propagation in soil microcosms exposed to conventional (polyethylene, PE) or biodegradable (polybutylene adipate terephthalate, PBAT) microplastics and four-generation tetracyclines. Compared with PBAT-only, the total abundance of ARGs increases progressively in soils co-exposed to PBAT and tetracyclines, ranging from 1.17-fold for the first-generation tetracycline to 2.87-fold for the fourth-generation tetracycline. Tetracycline and multidrug ARGs are markedly enriched under PBAT combined with high-generation tetracyclines, particularly fourth-generation omadacycline. This ARG proliferation coincides with generational enrichment of opportunistic taxa, whereas sensitive taxa exhibited weak or negative correlations. Molecular docking simulations reveal that enhanced resistance potential of opportunistic taxa stems from stronger binding affinities between resistance proteins and high-generation tetracyclines. These findings highlight the pivotal role of opportunistic microbes in ARG dissemination under biodegradable microplastics and newer antibiotic generations, advancing our mechanistic understanding of resistance proliferation in soil ecosystems. Strong binding of resistance proteins to high-generation tetracyclines exacerbates antibiotic resistance gene spread in soil exposed to biodegradable polybutylene adipate terephthalate and tetracyclines, based on soil microcosm experiments.