The ablation cycle drives glacier microbiome dynamics and downstream dissemination risk of the resistome.

Glacial ecosystems on the Tibetan Plateau undergo pronounced hydrological shifts across the glacial ablation cycle, driven by the onset and retreat of the Indian summer monsoon. To elucidate how transitions between four distinct hydrological ablation stages (pre-ablation, early ablation, late ablation, and frozen) shape microbial community structures and antibiotic resistance gene (ARG) profiles, we analyzed 112 samples collected across four stages from multiple glacier catchments on the southeastern Tibetan Plateau using metagenomic sequencing. Our results indicated that warmer stages favored thermotolerant Proteobacteria and reduced overall community diversity and evenness. ARG abundances exhibited ablation-dependent fluctuations, with Betaproteobacteria identified as predominant potential hosts. Furthermore, ARGs and virulence factors associated with mobile genetic elements were enriched during early and late ablation stages relative to the frozen stage, suggesting elevated potential for horizontal gene transfer coinciding with peak meltwater discharge. Notably, while upstream meltwaters generally exhibited higher ARG abundances, the upstream-downstream disparity tended to diminish from the pre-ablation to the late ablation stage, likely reflecting enhanced microbial mixing driven by glacier melt. Together, these findings reveal that glacier meltwater microbiomes are primarily shaped by ablation dynamics rather than spatial heterogeneity. More importantly, dynamics across the glacial ablation cycle drive shifts in meltwater hydrology that facilitate the downstream environmental mobility of glacial resistomes, posing growing antimicrobial resistance risks within the One Health framework.