Algae and Associated Viruses in a Marine-Derived Antarctic Lake

Over billions of years, the Ocean’s microbiome has evolved a plethora of lifestyles and adaptations. Viruses are an important force that can facilitate host resilience to a changing environment, influence community behavior, and participate in the cycles and fluxes of chemical elements. Here, we explore the ecophysiology of eukaryotic phytoplankton and their associated viruses in Ace Lake, a marine-derived lake in the Vestfold Hills region of Antarctica that has been isolated from the Southern Ocean for 5,000 years. Metagenomics analysis of microbial populations (>1TB shotgun data) within distinct layers of Ace Lake and across seasons revealed a microalgal community that included species in the orders Mamiellales, Chlorellales and Volvocales. A diverse dsDNA viral community, containing Nucleo-Cytoplasmic Large DNA Viruses (NCLDV), Polinton-like viruses (PLVs), and virophages, was found to be associated with these algae. Analysis of more than 15 million predicted proteins showed a seasonal variation of the viral community positively-correlated to the relative abundance of their inferred hosts. The metagenome-assembled genomes of 15 algae species contained homologs of NCLDV core genes involved in ATPase packaging, late transcription factors, sequence recognition, and insertion suggesting past host-virus interactions. Further examination of genomic data from viruses and eukaryotic single-celled organisms in the context of the local environmental conditions (e.g., low temperature, low light, hydrological and wind regime, low level of invasive species) opens new possibilities for assessing the impact of viral infection modes on productivity and community dynamics in Ace Lake.