Genomic adaptation of giant viruses in polar oceans

Abstract

Despite being perennially frigid, polar oceans form an ecosystem hosting high and unique biodiversity. Various organisms show different adaptive strategies in this habitat, but how viruses adapt to this environment is largely unknown. Viruses of phyla Nucleocytoviricota and Mirusviricota are groups of eukaryote-infecting large and giant DNA viruses with genomes encoding a variety of functions. Here, by leveraging the Global Ocean Eukaryotic Viral database, we investigate the biogeography and functional repertoire of these viruses at a global scale. We first confirm the existence of an ecological barrier that clearly separates polar and nonpolar viral communities, and then demonstrate that temperature drives dramatic changes in the virus–host network at the polar–nonpolar boundary. Ancestral niche reconstruction suggests that adaptation of these viruses to polar conditions has occurred repeatedly over the course of evolution, with polar-adapted viruses in the modern ocean being scattered across their phylogeny. Numerous viral genes are specifically associated with polar adaptation, although most of their homologues are not identified as polar-adaptive genes in eukaryotes. These results suggest that giant viruses adapt to cold environments by changing their functional repertoire, and this viral evolutionary strategy is distinct from the polar adaptation strategy of their hosts.

Distinct and rich assemblages of giant viruses in Arctic and Antarctic lakes

“…2A and B ). This implies the existence of other intrinsic factors that contribute to the unique characteristics of polar communities and suggests the existence of an ecological barrier separating temperate and polar lakes similar to the one recently shown in marine ecosystems [ 68 ]. In their study, Meng et al .…”

“…The greater proximity of Ace Lake to the ocean and its lack of ice cover could explain why more GVMAGs are shared with Milne Lake than with Lake A, which is ice-covered and not directly connected to the ocean. Further investigations should be led in this direction, and the recently generated polar/non-polar marine GVMAGs would be a relevant comparison point to search for overlap with marine data and potential role of oceans in interactions between polar lakes [ 68 ].…”

“…In their study, Meng et al . [ 68 ] identified numerous viral genes associated with polar adaptation and notably to cold environments by changing their functional repertoire. They noted that most of the homologues of these viral genes were not identified as polar-adaptive genes in their eukaryotic hosts, suggesting that viral evolutionary strategy was independent of the polar adaptation of their potential hosts.…”

Expansion of the genomic and functional diversity of global ocean giant viruses

“…A large number of these novel functions coming from polar or Baltic Sea GVMAGs could be further evidence of environmentally specific infection strategies or functional repertoires as is seen in other nutrient and light regimes [72,73]. Previous analysis of polar giant viruses also found high levels of adaptation and unique gene content compared to temperate and tropical counterparts [74], showing these colder environments could be reservoirs of novel encoded virus functions.…”

Extracellular rRNA profiling reveals the sinking and cell lysis dynamics of marine microeukaryotes

“…According to field experiments, viral infection eliminates 20-40% of plankton populations daily [7][8][9] . Recent studies have uncovered a remarkable heterogeneity of eukaryotic viruses in marine environments, implying that plankton species suffer from environmental viral infections [10][11][12] . However, utilizing viral abundance and distribution profiles to assess the cell death of each plankton species is currently infeasible as most viruses detected in the environment lack host information.…”