Bacterial spores from cold and hot origins resistant to simulating space environment

Microorganisms able to tolerate environmental extremes, or extremophiles, are ideal candidates to extend our knowledge on the limitations for terrestrial life, including sporicidal treatments, and also on their ability to survive at conditions mimicking space environments. In this work, we screened spores of bacilli from cold (Antarctic permafrost active layer) and hot-acid (shallow hydrothermal vents of Eolian Islands, Italy) environments for resistance to conditions simulating those of extraterrestrial surfaces (UV-C, wet-heat, pH3 and pH10). Studied spores were obtained from i) psychrotolerant strains from Antarctic permafrost: A30, A34, A43, A45, B51 and B58, and ii) thermophilic strains from shallow hydrothermal vents: Geobacillus vulcanii DSM13174 (Gv), Bacillus licheniformis T14 (T14), and Bacillus sp. P82. Suspensions of spores were exposed to the following stresses: UV-C radiation, until 1000 J/m2; wet-heat, 90°C for 60 min, and pH3 and pH10 in comparison with spores of B.subtlis 168 as well-known as bio-dosimetry strain for astrobiological studies. Spores fromB.subtilis 168 were themost resistant to UV-C (192J/m2) followed by the thermophilic Eolian strain T14 spores(LD90=187J/m2). Spores from the thermophilic strain Gv were the most resistant to wet-heat (2.82%). Spores from A34 showed the highest resistance to pH3 (12.7%), whereas those from strain A43 were the most resistant to pH10 (31.8%). The studied spores were capable to tolerate exposure to UV-C radiation never encountered in.This suggests that they are not radiation-resistant per se, but the mechanisms that extremophilic strains possess to protect themselves from high and low temperatures and pH (e. g., DNA repair and stabilization of spore DNA with ?/? type small acid soluble proteins) could be also determinant in resisting to the effects of UV-C radiation. These spores could have a relevant impact in Astrobiology, as novel bacterial multi-resistant models in the space exploration missions.