Diversity and biogeochemical roles of DNA viruses in Antarctic sea ice

Abstract

Abstract Background Polar sea ice is one of the largest ecosystems on Earth, harboring a vast and unexplored microbial diversity, which sustains the polar ecosystems during the long dark winters. Viruses are the most abundant “life forms” in the sea and are considered the main manipulators of microorganisms. However, little is known about the viral assemblages inhabiting Antarctic sea ice and under ice seawater or their biogeochemical roles. Results Here we establish an Antarctic sea ice and water DNA virome (ASIWV) dataset by analyzing 11 viral metagenomes derived from sea ice and seawater from below the melting ice in spring. A total of 28,169 viral contigs were identified and classified into 17,284 nonredundant viral Operational Taxonomic Units (vOTUs). Most of vOTUs could not be classified and so are considered probably endemic to Antarctic marine environments. Compared with those from sea water, viruses from within the sea ice preferentially adopted a lysogenic infection strategy, comprising more than 20% of viruses in multiple sea ice samples. The vOTUs in sea ice and sea water were quite similar, but there was still a distinction between their relative abundances. Potential hosts of 222 vOTUs were predicted, mainly linked to the dominant bacterial classes Gammaproteobacteria and Flavobacteriia. Notably, 220 virus-encoded auxiliary metabolic genes from 28 categories were identified, suggesting that viruses mediate microbial metabolism of carbon, sulfur, nitrogen, lipids and cold adaption. Conclusions This study is the first to reveal the unique taxonomic characteristics of viruses from polar sea ice and the under ice seawater, provides a baseline for sea ice DNA viral assemblages, highlights an unexplored hotspot of viral diversity and enhances our understanding of the viral contribution to the regulation microbial ecology and biogeochemistry.