A Desert Cyanobacterium under Simulated Mars-like Conditions in Low Earth Orbit: Implications for the Habitability of Mars

Abstract

In the ESA space experiment BIOMEX (BIOlogy and Mars EXperiment), dried Chroococcidiopsis cells were exposed to Mars-like conditions during the EXPOSE-R2 mission on the International Space Station. The samples were exposed to UV radiation for 469 days and to a Mars-like atmosphere for 722 days, approaching the conditions that could be faced on the surface of Mars. Once back on Earth, cell survival was tested by growth-dependent assays, while confocal laser scanning microscopy and PCR-based assay were used to analyze the accumulated damage in photosynthetic pigments (chlorophyll a and phycobiliproteins) and genomic DNA, respectively. Survival occurred only for dried cells (4-5 cell layers thick) mixed with the martian soil simulants P-MRS (phyllosilicatic martian regolith simulant) and S-MRS (sulfatic martian regolith simulant), and viability was only maintained for a few hours after space exposure to a total UV (wavelength from 200 to 400 nm) radiation dose of 492 MJ/m 2 (attenuated by 0.1% neutral density filters) and 0.5 Gy of ionizing radiation. These results have implications for the hypothesis that, during Mars's climatic history, desiccation-and radiationtolerant life-forms could have survived in habitable niches and protected niches while transported.

Limits of Life and the Habitability of Mars: The ESA Space Experiment BIOMEX on the ISS

“…(Huwe et al, 2019). Results obtained after space exposure are shown from a series of analyses on the biofilm kombucha (Podolich et al, 2019), the cyanobacterium Chroococcidiopsis (Billi et al, 2019), the cryptoendolithic Antarctic fungus Cryomyces antarcticus (Onofri et al, 2019), and the lichens Buellia frigida (Backhaus et al , this issue) and Circinaria gyrosa (de la Torre et al , not part of this issue). A rough summary of the different studies is given in Table 5, and more details are shown in Table 6.…”

Viroids-First—A Model for Life on Earth, Mars and Exoplanets

“…Another approach is taken by mimicking space-or Mars-like conditions in the laboratory [118][119][120]. Silicified sediments are analyzed for early signatures of life [121].…”

Carotenoid Raman Signatures Are Better Preserved in Dried Cells of the Desert Cyanobacterium Chroococcidiopsis than in Hydrated Counterparts after High-Dose Gamma Irradiation

“…Biomarker stability/degradation have, for instance, been evaluated in desert cyanobacteria of the genus Chroococcidiopsis exposed to different types of ionizing radiation [14] and Mars conditions simulated by using the EXPOSE facility installed outside the International Space Station [15].…”

“…During the EXPOSE-R2 space mission, in the contest of the BIOlogy and Mars Experiment (BIOMEX), dried cyanobacteria were mixed with Martian mineral analogues to mimic Martian subsurface radiation conditions reached by a reduced amount of UV radiation [21], such as it could be the case within potential subsurface or endolithic habitable niches. Dried Chroococcidiopsis cells mixed with Martian mineral analogues were exposed to a total dose of 2.19 × 10 2 kJ/m and 1.94 × 10 2 kJ/m UV radiation (200-400 nm), depending on the position inside the facility and presence of a 0.1% neutral filter [15], and 0.5 Gy of cosmic ionizing radiation [22]. Exposed cells with minerals showed a reduction in the photosynthetic pigments autofluorescence to about 20% of control while DNA could not be amplified in exposed cells not mixed with minerals [15].…”

“…Dried Chroococcidiopsis cells mixed with Martian mineral analogues were exposed to a total dose of 2.19 × 10 2 kJ/m and 1.94 × 10 2 kJ/m UV radiation (200-400 nm), depending on the position inside the facility and presence of a 0.1% neutral filter [15], and 0.5 Gy of cosmic ionizing radiation [22]. Exposed cells with minerals showed a reduction in the photosynthetic pigments autofluorescence to about 20% of control while DNA could not be amplified in exposed cells not mixed with minerals [15].…”