Investigating the impact of landfill age and season on the occurrence and dissemination of antibiotic resistance genes in leachate and the underlying mechanisms using metagenomics

AIMS: Antibiotic resistance genes (ARGs) pose a critical public health concern, with landfill leachate serving as a significant environmental reservoir. While ARG dynamics in leachate have been investigated in various contexts, their occurrence and influence factors in semi-arid regions remain poorly understood. This study investigated the occurrence and influence factors of ARG profiles, their potential hosts, and underlying mechanisms driving their proliferation. METHODS AND RESULTS: Comprehensive metagenomic analysis of leachate samples collected from landfills of varying landfill ages (5, 10, and 20 years) in Hohhot, Inner Mongolia-a representative semi-arid region of northern China-across three seasons (autumn, spring, and summer). Metagenomic analysis revealed distinct patterns in core ARG abundances modulated by both landfill age and seasonal variations. Notably, landfill age predominantly influenced tetracycline- and glycopeptide-ARGs, while seasonal fluctuations primarily affected glycopeptide- and multidrug-ARGs. Taxonomic analysis identified Pseudomonas aeruginosa and P. fluorescens as the predominant resistant pathogens, with elevated prevalence during spring and winter compared to summer. Network analysis and metabolic pathway reconstruction demonstrated that landfill age maybe impacted ARG dissemination through modulation of carbohydrate and nitrogen metabolic pathways. This novel finding suggests a previously unrecognized mechanism linking waste decomposition stages to ARG proliferation. CONCLUSIONS: Our study provides the first systematic characterization of ARG dynamics in semi-arid landfill leachate, offering crucial insights for developing targeted strategies to mitigate ARG dissemination in these distinct ecological contexts. These findings establish a theoretical framework for understanding ARG transmission in semi-arid environments, while providing empirical evidence to inform environmental management practices.