SURVIVAL LIMITS OF TERRESTRIAL EXTREMOPHILES RELEVANT FOR ICY MOONS IN OUR SOLAR SYSTEM

Kurzfassung

Astrobiological space research has expanded beyond Mars to include exploration of icy moons, as evidenced by ongoing missions to the outer solar system like NASA’s Europa Clipper and ESA’s JUICE mission, along with other missions in preparation. Icy moons, particularly Jupiter’s Europa and Saturn’s Enceladus, hold promise for discovering complex organic chemistry and potentially even life due to the presence of liquid water beneath their icy surfaces and a rocky core in contact with the subsurface oceans. The environmental conditions within these oceans pose challenges for terrestrial microorganisms, yet they are akin to certain Earth environments where specialized extremophiles thrive. The key question is whether these organisms could inadvertently contaminate the subsurface oceans of icy moons, if transported there by spacecraft. Organisms with the potential to contaminate icy moons must endure prolonged desiccation and vacuum exposure during the lengthy space journey, withstand extended periods of exposure to cosmic radiation, and they must be able replicate in low temperatures under oligotrophic and anoxic conditions in the presence of salts within or beneath the ice. Our study investigates the survival limits of extremophilic microorganisms across the three domains of life under simulated space conditions to assess their viability and potential proliferation on other planetary bodies, specifically the icy moons. Concentrating on psychrophilic and psychrotolerant microorganisms from icy moon analog environments like the Canadian High Arctic and Antarctica, as well as cleanrooms, the research seeks to mimic the challenges faced by microorganisms during outer solar system travel on spacecraft, potentially impacting the subsurface oceans of icy moons. The microorganisms were cultured under oligotrophic conditions in minimal media with only a single carbon source, subjected to extreme temperature fluctuations, freeze-thaw cycles, and radiation comparable to the conditions encountered during voyages to the outer solar system. Interestingly, the resistance of the tested microorganisms to the environmental stressors varied among the different species, even if they originated fromsimilar habitats on Earth. Surprisingly, even yeasts from moderate environments and humanassociated species exhibited versatility and resistance to extreme environmental conditions like those encountered during a space mission to icy moons. The insights gained, together with forthcoming metagenome data and phenotype prediction tools, will help pinpoint planetary protection-relevant microorganisms within cleanrooms and spacecraft, aiding in the development of tailored planetary protection strategies for missions to icy moons.