High diversity of the viral community from an Antarctic lake.

Viruses are the most abundant biological entities and can control microbial communities, but their identity in terrestrial and freshwater Antarctic ecosystems is unknown. The genetic structure of an Antarctic lake viral community revealed unexpected genetic richness distributed across the highest number of viral families that have been found to date in aquatic viral metagenomes. In contrast to other known aquatic viromes, which are dominated by bacteriophage sequences, this Antarctic virus assemblage had a large proportion of sequences related to eukaryotic viruses, including phycodnaviruses and single-stranded DNA (ssDNA) viruses not previously identified in aquatic environments. We also observed that the transition from an ice-covered lake in spring to an open-water lake in summer led to a change from a ssDNA- to a double-stranded DNA-virus-dominated assemblage, possibly reflecting a seasonal shift in host organisms.