Sinking particles as repository of antimicrobial resistome diversity in the Sansha Yongle Blue Hole

The aquatic environment plays a central role in the selection and spread of antimicrobial resistance genes (ARGs). Using metagenomic approaches, several studies have provided a comprehensive view of the antimicrobial resistome across different aquatic ecosystems. However, unique aquatic systems, such as oceanic blue holes, remain largely unexplored. Free-living and particle-associated samples from the Sansha Yongle Blue Hole (South China Sea) were analyzed by shotgun metagenomics to characterize the antimicrobial resistome and the potential mobility of detected ARGs. The diversity of the antimicrobial resistome significantly decreased with increasing water depth. This trend was driven by the free-living bacterial community, whereas it remained stable in particle-associated communities. Additionally, the latter showed a higher frequency of co-occurring ARGs and mobile genetic elements on the same contigs, with a frequent plasmid localization of these genes. Overall, particle-associated bacteria proved essential for sustaining antimicrobial resistome diversity. Furthermore, these findings suggest that horizontal transfer of ARG may be more frequent within particle-associated communities along the water column of the blue holes, potentially contributing to the persistence of resistances in deep marine waters.