Extremophiles exhibit extraordinary tolerance to extremes of, for example, temperature, pH, or salinity. Astrobiology 15, 1076–1090.Į xtremophiles are organisms surviving in environments considered to be physically or chemically extreme (Rothschild and Mancinelli, 2001). Key Words: Extremophiles- Halomonas sp.-Antarctica-Mars-Ionizing radiation-Cosmic rays. Consequently, the survival of the cold-, desiccation-, and radiation-resistant organisms isolated here has implications for the potential habitability of dormant or cryopreserved life on Mars. Irradiation at −79☌ (representative of average martian surface temperatures) increases the microbial radiation resistance 9-fold. A strong correlation was found between desiccation and radiation resistance, indicating that an increase in the desiccation resistance of 5 days corresponds to an increase in the room-temperature irradiation survival of 1 kGy. Thus, a meta-analysis of scientific literature was conducted to gather a larger data set. In addition, the association between desiccation and radiation resistance has not been investigated quantitatively before for a broad diversity of microorganisms. They were studied here for the first time for both their desiccation and irradiation survival characteristics. Halomonads, identified by 16S rRNA gene sequencing, were the most numerous survivors of the highest irradiation exposures. This is the first study to isolate radiation-resistant microbes by using gamma-ray exposure preselection from the extreme cold desert of the Antarctic Dry Valleys (a martian surface analogue). Desert soils are, therefore, promising targets to prospect for new radiation-resistant strains. Radiation resistance is believed to be an incidental adaptation to desiccation resistance, as both hazards cause similar cellular damage. Extreme radiation–resistant microorganisms can survive doses of ionizing radiation far greater than are present in the natural environment.
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