Metagenomic analysis reveals Northwest Pacific Ocean as a reservoir and evolutionary hub of antibiotic resistance genes.

Antibiotic resistance genes (ARGs) were identified as a novel type of environmental contaminants. Ocean is thought to be one of the ultimate environments where ARGs gathered. Marine ecosystems represent vast reservoirs of ARGs, yet their dynamics in open-ocean environments remain poorly characterized. Through large-scale metagenomic profiling of the Kuroshio Extension, a hydrographically dynamic region in the Northwest Pacific, we identified a striking enrichment of ARGs (1.81 × 10-3 ratio) at a frontal zone site (S30). The ARG abundance at this site exceeded coastal levels by 90-fold. Notably, multidrug resistance genes dominated this hotspot, with efflux pumps contributing 62 % of the resistance mechanisms, a pattern distinct from the target-alteration strategies prevalent in other regions. The site exhibited unique microbial consortia, including pathogenic Acinetobacter (30.2 % abundance) carrying clinically critical determinants (msbA, adeJ). Co-occurrence networks revealed horizontal transfer risks, linking clinical pathogen and nature carrier to multiple ARGs. Crucially, we discovered three novel plasmid-borne resistance genes circulating in >15 % of microbial populations, demonstrating open-ocean ARG diversification independent of direct anthropogenic inputs. These findings redefine oceanic frontiers as crucibles of resistance evolution, demanding urgent integration into global antimicrobial stewardship strategies.