Antimicrobial resistance gene diversity, prevalence, and mobility within four landfills

Antibiotics in landfills create selection pressures on the microorganisms present, selecting for antibiotic resistance genes (ARGs) and antibiotic resistant organisms (ARO). The aim of this study was to assess whether landfills are hot-spots of antimicrobial resistance and whether landfills may contribute to global ARO diversity through ARG lateral gene transfer. Genome resolved metagenomic sequencing combined with sequence-search-based and deep learning tools were used to determine ARG diversity and prevalence from four active municipal landfills and their adjacent ground or surface water systems. Comparison to pristine and anthropogenic environments highlighted that landfill microbial communities contain distinct ARG signatures, including a broader diversity of ARGs. Plasmids made up 4.1%-8.4% of assembled scaffolds and carried 5.4%-12.0% of the identified ARGs in assembled data, depending on the sample type. Enriched ARG resistance mechanisms on mobile elements included multidrug resistance and antibiotic inactivation. The results indicate that landfills house a high diversity of antimicrobial resistance mechanisms and drug classes, with a moderate fraction encoded on mobile elements. Landfills are thus likely mixing grounds for ARG transfer and evolution of novel or augmented ARO lineages.