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

摘要

In the ESA space experiment BIOMEX (BIOlogy and Mars EXperiment), dried iChroococcidiopsis 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 ia 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 radiation-tolerant life-forms could have survived in habitable niches and protected niches while transported.