Viral diversity and activity in Arctic tundra soils in wintertime

Arctic soils store vast amounts of carbon and are warming faster than the rest of the globe. Still, little is known about microbe-mediated feedback responses to the ongoing environmental changes in the warming Arctic. Specifically, viral diversity, functions, and virus-host interactions remain largely unknown in northern soils outside the growing season. Here, we analyzed the diversity and activity of viruses in oroarctic tundra soils during wintertime using metatranscriptomics. Through de novo virus prediction as well as targeted searches, we identified 995 viral operational taxonomic units (vOTUs) in total. Most of these vOTUs, 93%, represented RNA viruses, part of which were presumably segments of multipartite genomes. RNA vOTUs were classified mainly within the phyla Lenarviricota (259), Kitrinoviricota (198), Pisuviricota (135), Ambiviricota (103), Negarnaviricota (79), and Duplornaviricota (42). Thirty-seven DNA vOTUs (mostly Caudoviricetes) were also detected, suggesting active viral infections. In total, 81% of all vOTUs were assigned with a putative host organism, mostly fungi (515 vOTUs). Viral communities were distinct across vegetation types, and pH and moisture contributed to the differences. Putative novel clades within Ambiviricota and Orpoviricetes were identified, expanding their known diversity. The study contributes to uncovering diverse RNA viruses and viroid-like elements in Arctic tundra soils and highlights that soil viruses remain active in wintertime.