Virus-host interactions in iron-oxidizing mats of the East Pacific Rise.

Iron-oxidizing microbial mats are commonly encountered features at low-temperature (<100˚C) hydrothermal vents found along the seafloor at tectonically active settings. The microbial communities in these mats are uniquely adapted to exploit the specific ecological niches within the physical and chemical gradients of their environment. A vital component for these adaptations is viral infections, although their impacts are poorly constrained. While the microbial communities of iron-oxidizing mats at seafloor hydrothermal vents have been well studied, the role of viruses in affecting these communities with respect to biogeochemical cycling, diversity, and/or population control remains unclear. The goal of this study was to assess the role and impact of viruses within iron-oxidizing mats of the well-studied 9˚N East Pacific Rise (EPR) segment. We found unique viral assemblages at each site, with 41% of the viral operational taxonomic units (vOTUs) shared across all sites, but with differing relative abundances. The virally-encoded auxiliary metabolic genes (AMGs) were also differentially abundant among the sites and included processes related to carbon and sulfur cycling. Virus-host linkages showed that the viral assemblages infect different members of the microbial communities within each mat, as well as the potential to affect ecological shifts in the metabolisms of various hosts due to viral infection, which could affect the rates of microbial processes. In these iron-oxidizing mats, viruses are therefore likely playing a role in the diversity and evolution of the microbial taxa through lysis and the potential to alter host metabolisms. Exploration of virus-host dynamics within iron-oxidizing mats in hydrothermal vent systems like the EPR aid in constraining a vital component of the deep ocean food webs and give critical insight to the ecology of these productive microbial communities.