In the ocean, viruses impact microbial mortality, regulate biogeochemical cycling, and alter the metabolic potential of microbial lineages. At deep-sea hydrothermal vents, abundant viruses infect a wide range of hosts among the archaea and bacteria that inhabit these dynamic habitats. However, little is known about viral diversity, host range, and biogeography across different vent ecosystems, which has important implications for how viruses manipulate microbial function and evolution. Here, we

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... examined viral diversity, viral and host distribution, and viral-host interactions in venting fluids from two geographically distant hydrothermal systems, the Mid-Cayman Rise in the Caribbean Sea and Axial Seamount in the Pacific Ocean. Analysis of viral sequences and CRISPR spacers revealed highly diverse viral assemblages and abundant lysogenic viruses, with 40% of metagenome-assembled genomes encoding a putative prophage. Network analysis revealed that viral host range was relatively narrow, with very few viruses infecting multiple microbial lineages. Viruses were largely endemic to individual vent sites, indicating restricted dispersal, and in some cases viral assemblages persisted over time. Thus, while the viruses at deep-sea hydrothermal systems play an important role in driving the evolution and ecology of resident vent microbial communities, their influence is highly localized to specific regions and taxa.