Survival limits of yeasts and other extremophilic microorganisms with relevance for planetary protection of the icy moons

Investigating the survival limits of extremophilic microorganisms exposed to simulated space conditions can shed light on the ability of terrestrial microorganisms to survive and propagate on other planetary bodies. Although microbes can be found in all environmental niches on Earth, this study focuses mainly on psychrophilic and psychrotolerant microorganisms (prokaryotes and eukaryotes) which have been isolated from locations of interest such as icy moon analogue environments and cleanrooms, and which might be of concern for forward planetary protection. Our research aimed to reproduce conditions for microorganisms on spacecraft travelling to the outer solar system, which could contaminate the icy moon’s subsurface oceans. The microorganisms were grown under oligotrophic conditions in minimal media supplemented with only a single carbon source and exposed to extreme conditions, in terms of temperature and radiation, as they occur during space travel to the outer solar system. Our results, in combination with future metagenome data and phenotype prediction tools, will allow the identification of planetary protection-relevant microorganisms in spacecraft assembly cleanrooms and on spacecraft and support the development of target-oriented planetary protection constraints for missions to the icy moons.

Methods
Methods included growth of microorganisms in minimal media, exposure to desiccation, polychromatic UV, UV-C and X-ray radiation.