1,4,1,- 1University of California San Diego (UCSD), Scripps Institution of Oceanography, United States of America (eskoog@ucsd.edu)
- 2Stanford University, Stanford, CA 94305, USA
- 3Georgia Institute of Technology, Atlanta, GA 30332, USA
- 4Cornell University, Ithaca, NY 14853, USA
- *A full list of authors appears at the end of the abstract
Viruses are the most abundant biological entities on Earth and exert powerful controls on ecosystem ecology, biogeochemical cycling, and microbial evolution. Hypersaline environments host the highest reported viral abundances of any aquatic system, yet little is known about how salinity and other environmental extremes influence viral ecology. In these systems, salinity alongside acidity strongly influence the isoelectric point (pI) of viral particles – the pH at which a virion carries no net surface charge – which affects viral particle electrostatic interactions and stability. When environmental pH approaches the pI of the viral structural proteome, virions lose surface charge, aggregate, and adsorb to particles, reducing viral infectivity. This, in turn, greatly influences microbial ecology and ecosystem-scale biogeochemical cycling. In this study, we use acidic and alkaline hypersaline lakes in Western Australia as a natural Earth-system laboratory to test how pH and salinity shape viral ecogenomics and microbial evolution. We analyzed metagenomes and viromes from 37 polyextreme lakes spanning pH 2.3-9.4 and 30-465 ppt salinity across wet and dry seasons, recovering 11,804 viral populations from 50 families along with 645 microbial metagenome-assembled genomes. We calculated the pI for viral structural proteomes and placed these data in a global context using viral genomes from environments spanning freshwater, soda lakes, acidic meromictic lakes, and deep-sea hydrothermal vents. Across all environments, viral structural pI distributions were strongly skewed toward more acidic values, with the most acidic capsids occurring in hypersaline and alkaline brines. Even modest shifts in viral structural pIs (~0.8 pH units) correspond to order-of-magnitude changes in proton concentration, suggesting physicochemical selection. Within cosmopolitan viral families, structural pI shifted systematically across pH-salinity regimes, demonstrating that structural traits are not fixed by phylogeny alone but respond to environmental geochemistry. Viruses infecting halophilic archaea exhibited the most acidic and most tightly constrained structural pI values, pointing to host envelope chemistry and host ecology as an additional filter on viral evolution. To understand how viruses may influence microbial adaptation to these environmental extremes, we also functionally characterized viral auxiliary metabolic genes (AMGs) and genes encoded on plasmids. Viral AMGs primarily supported host energy metabolism rather than stress tolerance, whereas plasmids encoded extensive osmotic and acid-stress pathways that were strongly structured across pH-salinity space, identifying plasmids as key agents of microbial adaptation in extreme brines. By linking viral and plasmid omics to geochemical gradients across a natural Earth-system laboratory, this work shows how molecular-scale traits scale up to shape ecosystem function and biogeochemical dynamics across the planet.
Emilie J. Skoog1, Benjamin Klempay1, Margaret M. Weng2, Steffen Beussecker3, Margaret A. Birmingham4, Peter T. Doran5, Luke A. Fisher1, Ellery D. Ingall6, Arthur Odenheimer5, Emily R. Paris3, Chad I. Pozarycki6, Taylor Plattner6, Hunter Jamison7, Nicole M. Fernandez8, Enrica Quartini7, Amina T. Schartup1, Cathryn D. Sephus1, Sanjoy M. Som9, Jessica M. Weber10, Britney E. Schmidt7, Jeff S. Bowman1, the Esperance Tjaltjraak Native Title Aboriginal Corporation, and the OAST Team 1Scripps Institution of Oceanography, UC San Diego, La Jolla, CA 92037, USA 2Georgetown University, Washington, DC 20057, USA 3Stanford University, Stanford, CA 94305, USA 4University of Kansas, Lawrence, KS 66045, USA 5Louisiana State University, Baton Rouge, LA 70803, USA 6Georgia Institute of Technology, Atlanta, GA 30332, USA 7Cornell University, Ithaca, NY 14853, USA 8Department of Earth and Planetary Sciences, ETH Zürich, 8092 Zürich, Switzerland 9Blue Marble Space Institute of Science, Seattle, WA 98104, USA 10NASA Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
How to cite: Skoog, E. J., Klempay, B., Weng, M. M., Fisher, L. A., Plattner, T., Schmidt, B. E., and Bowman, J. S. and the OAST Team: Acidity and salinity influence viral ecogenomics and microbial evolution in polyextreme lakes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19252, https://doi.org/10.5194/egusphere-egu26-19252, 2026.
