Investigating the role of icy moon-relevant psychrotolerant microorganisms and the role of extremophilic yeasts

Kurzfassung

Extremophilic microorganisms play a key role in the identification of the habitability of celestial bodies. Excluding Mars, two other locations in the Solar System could support life, the icy moons of Jupiter and Saturn, Europa and Enceladus respectively. Space missions starting in the 1970s have already elucidated the environmental characteristics of these moons, however, with the launch of the Jupiter icy moons explorer (JUICE) and Europa clipper missions, our understanding of the environmental characteristics of these locations will be improved. On Earth, the analysis of the adaptation strategies of psychrotolerant microorganisms, isolated from analogue environments, such as Antarctic and high arctic ones, will elucidate how these celestial bodies could support life. To identify microbial organisms capable of tolerating icy moon conditions, we selected one psychrotolerant microorganism from each domain of life. Growth was performed under oligotrophic media conditions. To simulate space conditions, we exposed the organisms to the following: desiccation at different temperatures, UV-C (254 nm) and polychromatic UV (200-400 nm) radiation, X-ray radiation and freezing and thawing cycles without additional cryoprotectants to determine their survival. Our results revealed that the yeasts were more tolerant than the investigated bacteria and that the yeast Rhodotorula frigidalcoholis was the most tolerant under all exposure conditions. Therefore, in order to reflect more accurately the extreme conditions of the icy moons, we exposed R. frigidalcoholis to combined conditions. Remarkably the yeast can tolerate 7 days of desiccation combined with 7500 J/m² of polychromatic UV and 750 Gy of X-ray radiation at 200 kV and 15 mA. We then isolated the RNA of the yeast prior to, during, and after exposure we were able to identify a high number of differentially expressed genes. Undoubtedly the damage the yeast cells received during exposure to the icy moon conditions requires repair for survival. The transcriptomic analyses we performed revealed the capability of the yeast to perform metabolic functions under desiccated state. Furthermore, the analysis shows the yeast halts cell cycle progression to upregulate DNA repair genes and cell structure components. Our study reveals how important multifactorial studies are for astrobiology and the role fungal candidates play as extremophiles and for the forward planetary protection of the icy moons.