Halophilic archaea as prime candidates for astrobiological research.

Introduction: The quest of exploring and looking for life in unusual or extreme places has been a human desire since centuries. Nowadays, our endeavors start to focus on the exploration of nearby planets in our solar system and the fascinating possibility to find extant life on one of these planets. Recent studies have increased our confidence that liquid water exists in form of high saline brines on the surface of Mars. Such brines may be similar to high salinity environments here on Earth such as solar salterns or salt lakes in Antarctica. The predominant inhabitants of these environments on Earth are halophilic Archaea. These or-ganisms are not only adapted to high osmotic condi-tions, but also to high radiation and fluctuations in temperature. Numerous studies have shown that differ-ent representatives of this family can cope with a wide variety of stress factors such as changes in osmotic pressure, ionizing radiation, different regimes of UV, exposure to simulated microgravity, exposure to Low Earth Orbit (LEO) and a high resistance to prolonged desiccation. Here we report on the resistance of halophilic archaea against bombardment with HZE-particles, their ability to survive in simulated Martian brines as well as the survival following exposure to outer space for 1.5 years during the EXPOSE-R2 mission