Microplastic aging mediates bacterial and antibiotic resistance gene composition in plastisphere and the associated...

Microplastics (MPs) and antibiotic resistance genes (ARGs) are emerging contaminants that have garnered significant attention due to their prevalence in soil. Although many studies have already highlighted the effects of MPs on soil microbial communities and ARGs spread, their differential variation in both habitats (plastisphere and surrounding soil solution) and the effect of aging degree of MPs has not been clarified. Herein, we conducted a microcosm experiment to investigate the effects of aged-treated MPs on microbiome and antibiotic resistome of the plastisphere and the surrounding soil solution. The results showed that MPs with different aging degree altered bacterial community compositions. The plastisphere was enriched more unique bacterial species compared to its surrounding solution, particularly for 7d-aged MPs. MPs aging promoted certain ARGs dissemination, which depends on habitats, ARGs types and their aging degree. MPs always promoted the enrichment of Proteobacteria as the top host, especially aged MPs, which explained the enhanced ARGs dissemination after aged MPs addition. The primary hosts of most ARGs shifted from surrounding soil solution to the plastisphere. In addition to these individual host species, population hosts, including key taxa within co-occurrence network modules and functional bacterial populations, also contributed to ARGs dissemination. Unique bacteria from the plastisphere were included in network key modules and promoted ARGs dissemination, but not in the solution. Bacterial functions and pathways both played pivotal roles in ARGs dissemination. Interestingly, the influence of these population-level hosts, along with associated bacterial functions and metabolic pathways, on ARG spread was more pronounced in the surrounding soil solution than in the plastisphere. According to variance partitioning analysis, horizontal gene transfer via MGEs plays an important role in ARGs dissemination with 54-78 % contribution in two habitats. Overall, these findings provide the differential processes and driving mechanisms of ARGs dissemination between the plastisphere and surrounding soil solution.