Viral genetic diversity and functional potential in polar and subarctic sea ice.

Sea ice plays a critical role in regulating the global climate and serves as a unique habitat for diverse microbial communities. Still, our understanding of viruses in these communities remains limited. To further uncover the diversity and functional potential of viruses in polar and subarctic sea ice, we explored the viral component of Arctic, Baltic Sea, and Antarctic sea ice metagenomes. Altogether, 550 viral operational taxonomic units (vOTUs) were recovered, most of which were putatively classified within the class Caudoviricetes, which comprises bacterial and archaeal tailed double-stranded DNA viruses. Hosts were predicted for 187 vOTUs, with Gammaproteobacteria and Bacteroidia being the most prevalent viral host groups. Potential functions were assigned for 56% of predicted viral gene products, including putative auxiliary metabolic genes (AMGs) involved in oxidative metabolism, photosynthesis, and metabolism regulation under stress conditions. Related viral genomes carrying similar AMGs were detected in other Arctic and more geographically distant freshwater, marine, and ice environments. Genus- and/or family-level links between the studied vOTUs were detected across samples. Our results suggest diverse and complex virus-host interactions in sea ice and highlight the essential roles viruses may play in sea ice ecosystem dynamics across polar and subpolar environments.