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

• Published in: Microbiome
• Main Authors: Zhi-Ping Zhong, Dean Vik, Josephine Z. Rapp, Olivier Zablocki, Heather Maughan, Ben Temperton, Jody W. Deming, Matthew B. Sullivan
• Format: Article in Journal/Newspaper
• Language: English
• Published: BMC 2023
• Subjects: Arctic; Viruses; Subzero and hypersaline brines; Cryopeg brine; Sea ice brine; Long- and short-read viromics; Microbial ecology; QR100-130; Climate change; Ice; permafrost; Sea ice
• Online Access: https://doi.org/10.1186/s40168-023-01619-6; https://doaj.org/article/90bc24c2f46849efa3163e287a76892f

Abstract Background Climate change threatens Earth’s ice-based ecosystems which currently offer archives and eco-evolutionary experiments in the extreme. Arctic cryopeg brine (marine-derived, within permafrost) and sea ice brine, similar in subzero temperature and high salinity but different in temporal stability, are inhabited by microbes adapted to these extreme conditions. However, little is known about their viruses (community composition, diversity, interaction with hosts, or evolution) or how they might respond to geologically stable cryopeg versus fluctuating sea ice conditions. Results We used long- and short-read viromics and metatranscriptomics to study viruses in Arctic cryopeg brine, sea ice brine, and underlying seawater, recovering 11,088 vOTUs (~species-level taxonomic unit), a 4.4-fold increase of known viruses in these brines. More specifically, the long-read-powered viromes doubled the number of longer (≥25 kb) vOTUs generated and recovered more hypervariable regions by >5-fold compared to short-read viromes. Distribution assessment, by comparing to known viruses in public databases, supported that cryopeg brine viruses were of marine origin yet distinct from either sea ice brine or seawater viruses, while 94% of sea ice brine viruses were also present in seawater. A virus-encoded, ecologically important exopolysaccharide biosynthesis gene was identified, and many viruses (~half of metatranscriptome-inferred “active” vOTUs) were predicted as actively infecting the dominant microbial genera Marinobacter and Polaribacter in cryopeg and sea ice brines, respectively. Evolutionarily, microdiversity (intra-species genetic variations) analyses suggested that viruses within the stable cryopeg brine were under significantly lower evolutionary pressures than those in the fluctuating sea ice environment, while many sea ice brine virus-tail genes were under positive selection, indicating virus-host co-evolutionary arms races. Conclusions Our results confirmed the benefits of long-read-powered viromics ...