The deep-ocean accounts for the majority of the water on our planet. While the cold deep-ocean is the dominant nutrient-challenged ecosystem, hydrothermal vents represent oases along tectonically active areas of the seafloor. Hydrothermal vents and the surrounding cold deep-ocean each support unique communities of microbes and viruses that have become highly adapted to local conditions. Through cycles of infection and host cell lysis, bacteriophages (viruses that specifically infect prokaryotes) have the potential to substantially influence the adaptation and population biology of their hosts. In order to investigate the community dynamics of microbes and viruses inhabiting two very different ecosystems, water samples were collected from a deep-ocean diffuse-flow hydrothermal vent and the surrounding cold bottom waters. Microbial communities were size-fractionated, in situ, by serial filtration onto membrane filters and viruses were concentrated via tangential flow filtration under ambient temperature and pressure. Metagenomic analysis of the organisms captured within the 0.1μm-0.8μm size fraction indicates that hydrothermal vent and cold deep-ocean ecosystems harbor taxonomically and functionally unique microbial communities; demonstrated by site-specific protein clusters and dominant microbial taxa. Preliminary analysis of sister viral metagenomic libraries indicate that viruses endemic to the deep-ocean contain a high frequency of novel genes and may play an important role in the adaptation of their microbial hosts to the very different, but equally challenging environmental conditions that characterize deep-ocean environments. Together, these observations suggest that microbial diversity and function in the deep-ocean is significantly influenced by the viruses that parasitize them.
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