The (deep) continental subsurface is home to a great abundance and diversity of archaea and bacteria, yet little is known about the viruses that infect these organisms. Of particular interest are dominant primary producers as they jump-start the food chain in these oligotrophic ecosystems and could in theory be an important target for viruses. In this proposal we hypothesize that Altiarchaeota, an uncultivated group of autotrophic subsurface archaea that occur in hot spots across the globe, are frequent targets of novel viruses that consequently impact carbon cycling. Using a combination of several state-of-the-art approaches including genome-resolved metagenomics, metatranscriptomics, and genome-informed microscopy, this project will result in a comprehensive dataset of a uncultivated virus-host system in order to unravel the different infection stages of a virus in the actual ecosystem. The results of this proposal will shed new light on the diversity and function of deep subsurface viruses that infect autotropic archaea and thus alter carbon cycling in these environments.