Unveiling the occurrence, hosts and mobility potential of antibiotic resistance genes in the deep ocean

As emerging microbial contaminants, antibiotic resistance genes (ARGs) are widely reported in the neritic zone. However, the profiles of ARGs in the deep ocean have not yet been fully resolved. In this study, the distribution, hosts, and mobility potential of ARGs at different water depths in the Western Pacific (WP) were investigated and compared to those in Bohai Sea (BH) waters using environmental parameter measurements, amplicon sequencing, metagenomic assembly and binning approaches. Our results showed that the top eight most abundant known ARG types in WP and BH waters were multidrug (39.85%), peptide (14.98%), aminoglycoside (11.33%), macrolide-lincosamide-streptogramin (MLS, 4.06%), tetracycline (3.74%), beta-lactam (3.12%), fluoroquinolone (1.79%) and rifamycin (1.24%). The ARGs observed in mesopelagic and bathypelagic waters were abundant and diverse as those observed in neritic waters, indicating that deep-sea water could be another environmental reservoir for ARGs. For deep-sea ARGs, members from classes Gammaproteobacteria (70%) and Alphaproteobacteria (21.1%) were the most important potential hosts. In addition, mobile genetic element analysis suggested that the ARG migration potential in dee sea water (> 1000 m) was relatively high. Overall, our findings expanded the understanding of ARGs in deep seawater and provided guidance for ARG pollution control and risk prediction.