Simulated Discharge of Ballast Water Reveals Potential Contribution to Spread of Antibiotic Resistance Genes in Geographically Isolated Receiving Waters

<b>Background/Objectives:</b> The propagation of antibiotic resistance genes (ARGs) poses a huge threat to environmental and human health. The ballast water from ships has been recognized as an important vector of ARGs. However, little is known about how ballast water from geographically isolated water affects ARGs in receiving waters. <b>Methods:</b> Herein, we investigated the changes in ARGs in receiving water by microcosm experiments simulating the discharge of ballast water. <b>Results:</b> The simulated discharge of ballast water increased the abundances of target ARGs, which were 1.3-5.6-fold higher in the mixture of ballast water and receiving water (microcosm M) than in receiving water at the end of the experiment. The enrichment of target ARGs was significantly associated with MGEs. Moreover, the discharge of ballast water changed the microbial communities in receiving water. Further network analysis identified potential ARG hosts, such as <i>Pseudohongiella</i>a and <i>Amphritea</i>, with the abundance in microcosm M (0.23% and 0.036%) being higher than in receiving water (0.09% and 0.006%), the changes of which might be responsible for ARG variations. <b>Conclusions:</b> Overall, our findings suggest the discharge of ballast water might promote the spread of ARGs in different geographical waters and the corresponding ecological risks should not be ignored.