Metagenomics of PM2.5 in smelting areas
Smelting is a major anthropogenic source of heavy metals, which can drive antibiotic resistance via co-selective mechanisms. However, resistance determinants in smelting-associated fine particulate matter (PM2.5) remain poorly characterized. Here, we performed metagenomic and comparative genomic analyses on PM2.5 samples collected from eight active smelting sites in China. We identified 320 antibiotic resistance gene (ARG) subtypes spanning 21 classes and 279 metal resistance genes (MRGs) spanning 123 subtypes, with multidrug and beta-lactam ARGs, alongside multimetal, arsenic, iron, and copper MRGs, being most prevalent. ARG and MRG profiles were highly concordant across sites, and co-localization on contigs and MAGs, including plasmid-borne determinants in enriched Rhodococcus, Achromobacter, and Pandorea taxa, suggested genetic linkage. Importantly, smelting-derived hosts carried more resistance determinants than their counterparts from other habitats, and total ARG and MRG abundance significantly exceeded those in 20 urban-air metagenomes. Our findings establish smelting-impacted PM2.5 as a previously underappreciated reservoir of resistance elements and underscore the critical need to include atmospheric monitoring in routine resistome surveillance under the One Health framework.