Lower viral evolutionary pressure under stable versus fluctuating conditions in subzero Arctic brines

Area of Science:

• * Environmental microbiology and virology.
• * Cryosphere and extreme ecosystem research.
• * Genomic and evolutionary biology.

Background:

• * Climate change impacts Earth's ice-based ecosystems, which harbor unique microbial life.
• * Arctic cryopeg brine and sea ice brine host distinct microbial communities adapted to subzero temperatures and high salinity.
• * Viral communities in these brines remain largely uncharacterized, particularly their interactions and evolutionary responses to environmental stability.

Discussion:

• * Long-read viromics significantly enhances viral genome recovery and discovery in extreme environments.
• * Viruses in cryopeg brine are marine-derived but distinct from sea ice and seawater viruses, while sea ice viruses largely overlap with seawater communities.
• * Identified virus-encoded genes, such as those for exopolysaccharide biosynthesis, suggest active roles in host metabolism and ecosystem function.

Key Insights:

• * Over 11,000 viral operational taxonomic units (vOTUs) were recovered, a 4.4-fold increase in known brine viruses, with long-read sequencing proving superior for genomic completeness.
• * Viruses actively infect dominant microbes (Marinobacter, Polaribacter) in both cryopeg and sea ice brines, influencing their metabolism.
• * Viral evolution differs significantly: stable cryopeg viruses show lower evolutionary pressure, while sea ice viruses exhibit positive selection on tail genes, indicating host-virus co-evolution.

Outlook:

• * Long-read viromics is crucial for exploring the virosphere, expanding viral discovery, and enabling biological inference.
• * Viral activity in subzero brines impacts remote extreme ecosystems, emphasizing their ecological significance.
• * Understanding viral adaptation strategies in stable versus fluctuating cryospheric conditions is vital for predicting ecosystem responses to climate change.