UNLABELLED: Prokaryotes and mobile genetic elements (MGEs, such as viruses and plasmids) interact extensively, leading to horizontal gene transfer (HGT) and consequent microbial evolution and diversity. However, our knowledge of the interactions between MGEs in deep-sea hydrothermal ecosystems is limited. In this study, we adapted a phage-fluorescence IMPORTANCE: Deep-sea hydrothermal vents are hotspots for microbes. Several studies revealed that virus-mediated horizontal gene transfer (HGT) in deep-sea hydrothermal vent ecosystems may be crucial to the survival and stability of prokaryotes in these extreme environments. However, little is known about the interaction between viruses and other mobile genetic elements (MGEs, such as plasmids), and how their interactions influence virus-mediated HGT in these ecosystems. In this study, we adapted a phage-fluorescence