20.500.12556/DiRROS-15699 Effects of desiccation and freezing on microbial ionizing radiation survivability considerations for Mars sample return Increasingly, national space agencies are expanding their goals to include Mars exploration with sample return. To better protect Earth and its biosphere from potential extraterrestrial sources of contamination, as set forth in the Outer Space Treaty of 1967, international efforts to develop planetary protection measures strive to understand the danger of cross-contamination processes in Mars sample return missions. We aim to better understand the impact of the martian surface on microbial dormancy and survivability. Radiation resistance of microbes is a key parameter in considering survivability of microbes over geologic times on the frigid, arid surface of Mars that is bombarded by solar and galactic cosmic radiation. We tested the influence of desiccation and freezing on the ionizing radiation survival of six model microorganisms: vegetative cells of two bacteria (Deinococcus radiodurans, Escherichia coli) and a strain of budding yeast (Saccharomyces cerevisiae); and vegetative cells and endospores of three Bacillus bacteria (B. subtilis, B. megaterium, B. thuringiensis). Desiccation and freezing greatly increased radiation survival of vegetative polyploid microorganisms when applied separately, and when combined, desiccation and freezing increased radiation survival even more so. Thus, the radiation survival threshold of polyploid D. radiodurans cells can be extended from the already high value of 25 kGy in liquid culture to an astonishing 140 kGy when the cells are both desiccated and frozen. However, such synergistic radioprotective effects of desiccation and freezing were not observed in monogenomic or digenomic Bacillus cells and endospores, which are generally sterilized by 12 kGy. This difference is associated with a critical requirement for survivability under radiation, that is, repair of genome damage caused by radiation. Deinococcus radiodurans and S. cerevisiae accumulate similarly high levels of the Mn antioxidants that are required for extreme radiation resistance, as do endospores, though they greatly exceed spores in radioresistance because they contain multiple identical genome copies, which in D. radiodurans are joined by persistent Holliday junctions. We estimate ionizing radiation survival limits of polyploid DNA-based life-forms to be hundreds of millions of years of background radiation while buried in the martian subsurface. Our findings imply that forward contamination of Mars will essentially be permanent, and backward contamination is a possibility if life ever existed on Mars. ionizing radiation life on Mars astrobiology radiation fungi bacteria radiotolerance ekstremotoleranca ionizirajoče sevanje bakterije glive radiacija astrobiologija Mars življenje na drugih planetih življenje na Marsu true false true Angleški jezik Slovenski jezik Neznano 2022-11-03 07:49:29 2022-11-03 07:49:32 2022-11-04 03:34:49 0000-00-00 00:00:00 2022 0 0 str. 1337-1350 no. 11 Vol. 22 2022 0000-00-00 Zaloznikova Objavljeno NiDoloceno 0000-00-00 0000-00-00 2022-01-01 579:523.43 1531-1074 10.1089/ast.2022.0065 127593987 https://www.liebertpub.com/doi/10.1089/ast.2022.0065 1 0ad7e163-5b33-11ed-bea5-001a4af901a5 https://dirros.openscience.si/Dokument.php?lang=slv&id=20773 RAZ_Horne_William_H._2022.pdf RAZ_Horne_William_H._2022.pdf 1 49620760C9F60896644466FA840C161F ae790a3e183c3a67d6e4894dc0bc1a77fefbfcfe7048e55905296313fa4bf21b 246fe32d-5b33-11ed-bea5-001a4af901a5 https://dirros.openscience.si/Dokument.php?lang=slv&id=20774 Gozdarski inštitut Slovenije 0 0 0