Diversity of Antarctic sea ice and under-ice seawater RNA viruses.

UNLABELLED: Sea ice is vital to polar ecosystems and serves as a natural laboratory for studying microbial adaptations in extreme environments. Nevertheless, the diversity and ecology of Antarctic marine RNA viruses have not been sufficiently explored. Here, 11 metatranscriptomes from Antarctic sea ice and ice-associated environments were analyzed to characterize RNA viral communities and their ecological differentiation between sea ice and seawater. Diverse RNA viral lineages were identified, of which Cryppavirales and Picornavirales were dominant. Lenarviricota was predominant in sea ice, highlighting the differential distribution between the two ecosystems. Evolutionary analyses showed lower Ka/Ks values in sea ice-associated RNA viruses, suggesting stronger purifying constraints and a more conserved evolutionary pattern compared with under-ice seawater. More than half of the viral operational taxonomic units (vOTUs) could be assigned to hosts, primarily fungi and algae, suggesting a potential role for viruses in fungal-algal symbiotic/parasitic systems. This study provides new insights into the diversity and distinctiveness of RNA viruses in Antarctic sea ice-seawater systems. IMPORTANCE: Polar sea ice is a vital component of Antarctic ecosystems and plays an important role in climate regulation, yet the diversity and ecological roles of its viral communities remain largely unknown. This study documents the diversity and complexity of RNA viruses in Antarctic sea ice-seawater systems. The potential host lineages of RNA viruses in Antarctic sea ice were explored, shedding light on the cryptic RNA viral communities in these extreme environments. These findings provide important insights into the diversity and ecology of RNA viruses in these habitats, enhancing the understanding of polar viral ecology.