Distinct associations between polycyclic aromatic hydrocarbons with different molecular weights and antibiotic resistance gene distribution in river sediments of the Loess Plateau, China

Although polycyclic aromatic hydrocarbons (PAHs) are widely recognized to influence the distribution of antibiotic resistance genes (ARGs), the roles of PAHs with different molecular weights in shaping ARG patterns remain underexplored. It is hypothesized that different molecular weight PAHs can influence ARGs dissemination through shifts in microbial diversity. Here, the spatial distribution and concentrations of PAHs in Beiluo River sediments were evaluated, followed by an assessment of their relationships with ARG distribution and microbial community structure across 18 sampling sites. Metagenomic sequencing was used to characterize the distribution patterns of ARGs, mobile genetic elements (MGEs), and microbial communities. The partial least squares path model (PLS-PM) suggested that PAH molecular weight was differentially associated with microbial community structure and ARG distribution. Low- and medium-molecular-weight PAHs (PHE and ANT) were positively associated with the dominating phylum Pseudomonadota, which may act as potential ARG hosts and promote the transmission of dominant ARGs, especially bacitracin- and multidrug resistance genes. In contrast, the α-diversity indices of Acidobacteriota, which exhibited relatively low abundance, were negatively correlated with high-molecular-weight PAHs (BbF). The co-occurrence network analysis further suggested that this phylum may serve as a potential host for MLS- and tetracycline resistance genes. Overall, these results contribute to the understanding of interactions among persistent organic pollutants, microbiota, and ARGs in human-disturbed rivers and support the ecological risk evaluation and management of PAH-contaminated aquatic systems.