The dissemination of a broad-host-range ARG-carrying plasmid to putative pathogens across agricultural soils

The spread of antibiotic resistance genes (ARGs) in agricultural soils poses a major global health challenge, yet the magnitude and directionality of ARG dissemination within complex soil microbial communities remain poorly characterized. Here, we systematically quantified and tracked the dissemination of a broad-host-range ARG-carrying plasmid across 52 agricultural soils. Plasmid transfer and transconjugant communities were characterized using quantitative PCR, fluorescence-activated cell sorting, and 16S rRNA gene sequencing. Our results demonstrate that substantial ARG transfer occurred in soil microbial communities, with the abundance of disseminated plasmids approximately 30 times higher than those retained by residual donor cells. Multivariate analyses indicated that the donor survival rate was most strongly associated with variation in ARG dissemination, while soil fertility and heavy metals were negatively associated with dissemination. ARG acquisition occurred preferentially in phylogenetically related lineages, with dispersal limitation and homogeneous selection shaping the assembly of the transconjugant community. Notably, approximately 77% of disseminated ARGs were acquired by putative pathogenic taxa, despite their low relative abundance in the original soils. Partial least squares path modeling further suggested that donor survival may serve as a key mediator through which edaphic and microbial factors influence ARG transfer to putative pathogens. Collectively, our findings indicate that plasmid-borne ARGs are preferentially acquired by putative pathogens, and the extent of this acquisition is strongly associated with donor viability.