Probing the habitability of sulfuric acid rich subsurface lakes in Europa's ice shell via Sulfolobus/STIV integrated biogeochemical models

Experimentally modeling the habitability of extreme ocean world conditions, such as those on Jupiter's moon: Europa, would benefit from integrated microbe-virus model studies to provide both a microbial model and a virus capable of nutrient cycling.This work experimentally probes the microbe/virus combination Saci/STIV as a potential microbial model system for habitability studies of Europa's ice-ocean interface in subsurface lakes with implications for habitats with extreme conditions and fluid mixing.This study experimentally modeled archaea/virus-integrated systems in one primary set of conditions that fall within the range of conditions currently proposed for subsurface lakes (melt pockets) in Europa's ice shell: 3.5% salinity, pH 3, rich in Na + /Fe 2+ /Mg 2+ /SO 4 2-/H + , fluctuating dissolved oxygen (D.O.), and 1-2 °C to explore habitability limits and possible biosignatures within Europa's ice.Planktonic Sulfolobus acidocaldarius (Saci) lysogens of Sulfolobus Turreted Icosahedral Virus (STIV) were included for the determination of potential habitability and biosignatures in both models.Extensive elemental sulfur encrusted biofilm formation, biosulfur detection by Raman spectroscopy, viral mRNA/protein detection by RT-qPCR and western blotting, and successful viability assays under these conditions promote the Europa ice-ocean interface as a potentially habitable ocean world for extreme microbes such as Saci.Cold-adapted Saci, selected for after months of passaging in near 0 ℃ conditions, proved to thrive in the extensive sulfur-encrusted biofilm.Finally, biosulfur and viral major capsid proteins (MCPs), with inter-domain conserved double jelly roll morphologies, were identified as potential biosignatures for life on acidic icy ocean worlds.Such cryotolerant strains and the viral proteins proliferated from them may have applications not just in astrobiology, but also biotechnology in space science and beyond.