1.7. ORIGIN AND EVOLUTION OF LIFE, EXTREMOPHILES 69 OLE-8 Desert strains of Chroococcidiopsis under extreme conditions: lessons for the next Expose-R2 mis- sion on the ISS Mickael Baqu´ e 1 , Lisa Caflisch 1 , Giuliano Scalzi 1 , Daniela Billi 1 , Jean-Pierre Paul de Vera 2 , Elke Rabbow 3 , Petra Rettberg 3 1 University of Rome ”Tor Vergata”, via della ricerca scientifica, Italy (mickael.baque@gmail.com) 2 German Aerospace Center (DLR), Institute of Planetary Research, Berlin, Germany 3 German Aerospace Center (DLR), Institute of Aerospace Medicine, Radiation Biology Department, Germany Background: Desert strains of Chroococcidiopsis are astrobiological model sys- tems which have been used in several ground-based simulations and space ex- posures by using the Biopan and Expose facilities. In their natural environment they thrive at the dry limit of life in extremely arid hot and cold deserts, such as the Dry Valleys in Antarctica and the Atacama Desert in Chile. In these extreme environments Chroococcidiopsis cells survive in a dry, ametabolic state for pro- longed periods and restore active metabolism upon rewetting, a phenomenon known as anhydrobiosis (life without water). In addition to avoid and/or limit desiccation induced damage to sub-cellular components (Billi 2009), desert strains of Chroococcidiopsis withstand environmental stressors not currently met in nature, like ionizing-radiations as high as 15 kGy (Billi et al. 2000) and UVC radiation up to 13 kJ/m 2 (Baqu´ e et al. 2013). When dried and overlain by 3mm of grounded sandstone Chroococcidiopsis survived space and Mars sim- ulation (Billi et al. 2011). Currently, in the frame of two ESA experiments, Biofilm Organisms Surfing Space (BOSS) and BIOlogy and Mars Experiment (BIOMEX), selected for the next EXPOSE-R2 mission, Chroococcidiopsis have been exposed to ground-based simulations. In BOSS the hypothesis is tested if biofilm lifestyle is better suited to support long-term survival under space and Martian conditions than planktonic growth. While in BIOMEX the endurance of selected extremophiles mixed with lunar and Martian regolith analogues is tested (de Vera et al. 2012). Materials and Methods: Chroococcidiopsis sp. strain CCMEE 057 (Sinai Desert) and strain CCMEE 029 (Negev Desert) were