Exploring the Habitability of the Outer Solar System Icy Moons for the Extremotolerant Yeast Rhodotorula frigidalcoholis.

Psychrophilic and psychrotolerant microorganisms have the unique ability to grow below 0°C, which makes them ideal candidates for studying how life could survive on the icy moons of the solar system. The renewed interest, in view of the JUICE and Europe Clipper missions, to explore these locations has pushed for the identification of organisms which could survive on the icy moons. In this study we selected the extremophilic yeast Rhodotorula frigidalcoholis given its innate ability to grow between 30°C and -10°C and to survive a range of extreme conditions including x-ray, UV-C and polychromatic UV radiation, desiccation at different temperatures, and freeze-thaw cycles. We report the survival of R. frigidalcoholis under conditions analogous to those found on icy moons. Using transcriptomic approaches, we present novel insights into differential gene expression before, during, and after exposure to combined icy moon conditions. We also identified the rapid activation of genes involved in catalytic activity and DNA repair during exposure. Our results contribute to a better understanding of the survival mechanisms of psychrotolerant microorganisms in extreme environments and can inform future life-detection missions on moons such as Enceladus and Europa, also highlighting the need to consider yeasts in planetary protection efforts.