Preservation of Biomarkers from Cyanobacteria Mixed with Mars­Like Regolith Under Simulated Martian Atmosphere and UV Flux

Abstract

The space mission EXPOSE-R2 launched on the 24th of July 2014 to the International Space Station is carrying the BIOMEX (BIOlogy and Mars EXperiment) experiment aimed at investigating the endurance of extremophiles and stability of biomolecules under space and Mars-like conditions. In order to prepare the analyses of the returned samples, ground-based simulations were carried out in Planetary and Space Simulation facilities. During the ground-based simulations, Chroococcidiopsis cells mixed with two Martian mineral analogues (phyllosilicatic and sulfatic Mars regolith simulants) were exposed to a Martian simulated atmosphere combined or not with UV irradiation corresponding to the dose received during a 1-year-exposure in low Earth orbit (or half a Martian year on Mars). Cell survival and preservation of potential biomarkers such as photosynthetic and photoprotective pigments or DNA were assessed by colony forming ability assays, confocal laser scanning microscopy, Raman spectroscopy and PCR-based assays. DNA and photoprotective pigments (carotenoids) were detectable after simulations of the space mission (570 MJ/m(2) of UV 200-400 nm irradiation and Martian simulated atmosphere), even though signals were attenuated by the treatment. The fluorescence signal from photosynthetic pigments was differently preserved after UV irradiation, depending on the thickness of the samples. UV irradiation caused a high background fluorescence of the Martian mineral analogues, as revealed by Raman spectroscopy. Further investigation will be needed to ensure unambiguous identification and operations of future Mars missions. However, a 3-month exposure to a Martian simulated atmosphere showed no significant damaging effect on the tested cyanobacterial biosignatures, pointing out the relevance of the latter for future investigations after the EXPOSE-R2 mission. Data gathered during the ground-based simulations will contribute to interpret results from space experiments and guide our search for life on Mars.

Survival, DNA Integrity, and Ultrastructural Damage in Antarctic Cryptoendolithic Eukaryotic Microorganisms Exposed to Ionizing Radiation

“…A great deal of interest in astrobiology has recently been devoted to different biomolecules, including DNA, to establish a suitable biosignature. Recent studies have proved the persistence of both carotenoids and DNA to polychromatic UV irradiation (Baqué et al, 2016), while eukaryotic DNA remained well detectable after both polychromatic UV irradiation and cosmic rays in real space conditions (Onofri et al, 2015;Pacelli et al, 2016). The STARLIFE project (Moeller et al, 2017, in this issue) aims to characterize the effect of ionizing radiation of astrobiological relevance on different microorganisms.…”

Attenuation of Ultraviolet Radiation in Rocks and Minerals: Implications for Mars Science

“…Numerous studies have shown that organic molecules are quickly degraded under simulated Mars UV conditions (Baqué et al, ; Dartnell & Patel, ; Hintze et al, ; Poch et al, ; Stoker & Bullock, ; ten Kate et al, ). The destruction of the parent molecules occurs through the breaking of functional bonds, which creates radicals that can further damage the parent molecule (Ehrenfreund et al, ).…”

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

“…Cells were pelleted (10,000g for 5 min), washed twice and resuspended in 20 mL of sterile double distilled water. DNA was extracted by performing 3 cycles of freeze-thawing (-80°C for 10 min and 60°C for 1 min) followed by 10 min boiling, as previously optimized (Baqué et al, 2016). After centrifugation (10,000g for 10 min), DNA concentrations were determined using the Qubit dsDNA HS Assay Kit and a Qubit 2.0 Fluorometer (Invitrogen).…”