Hawaiian geothermal fumaroles contain diverse and novel viruses.

Viral community structure is known to influence the evolution of microbes in diverse and complex environments. While the diversity of microbes and their viruses have been metagenomically explored in terrestrial hot springs and hydrothermal vent systems, other volcanic features remain remarkably understudied. Fumaroles (steam vents) are geothermal features that heat groundwater with magma, releasing heated water vapor and volcanic gases, such as CO IMPORTANCE: Geothermal environments serve as natural laboratories for studying adaptations to extreme conditions that challenge the limits of microbial life and offer insight into early life on Earth. Exploring microbial diversity in these systems reveals how ecological factors shape complex communities in extreme environments. Evidence increasingly shows that viruses influence microbial diversity in terrestrial hot springs and oceanic hydrothermal vents, yet the biogeography of viruses across these systems remains largely unexplored. We present the first metagenomic characterization of viral diversity and ecology in Hawaiian terrestrial volcanic fumaroles. Our results indicate extensive viral dispersal, in contrast to the typically more constrained dispersal observed in hot springs and hydrothermal vent systems. Furthermore, we observe a dominance of ssDNA viruses in fumarole viral communities, a pattern not previously reported in terrestrial systems. Our comprehensive analyses indicate that Hawaiian fumaroles are a valuable system for studying community patterns and the ecological determinants of viral biogeography.