Effects of Long-Term Simulated Martian Conditions on a Freeze-Dried and Homogenized Bacterial Permafrost Community

Abstract

Indigenous bacteria and biomolecules (DNA and proteins) in a freeze-dried and homogenized Arctic permafrost were exposed to simulated martian conditions that correspond to about 80 days on the surface of Mars with respect to the accumulated UV dose. The simulation conditions included UV radiation, freeze-thaw cycles, the atmospheric gas composition, and pressure. The homogenized permafrost cores were subjected to repeated cycles of UV radiation for 3 h followed by 27 h without irradiation. The effects of the simulation conditions on the concentrations of biomolecules; numbers of viable, dead, and cultured bacteria; as well as the community structure were determined. Simulated martian conditions resulted in a significant reduction of the concentrations of DNA and amino acids in the uppermost 1.5 mm of the soil core. The total number of bacterial cells was reduced in the upper 9 mm of the soil core, while the number of viable cells was reduced in the upper 15 mm. The number of cultured aerobic bacteria was reduced in the upper 6 mm of the soil core, whereas the community structure of cultured anaerobic bacteria was relatively unaffected by the exposure conditions. As explanations for the observed changes, we propose three causes that might have been working on the biological material either individually or synergistically: (i) UV radiation, (ii) UV-generated reactive oxygen species, and (iii) freeze-thaw cycles. Currently, the production and action of reactive gases is only hypothetical and will be a central subject in future investigations. Overall, we conclude that in a stable environment (no wind-/pressure-induced mixing) biological material is efficiently shielded by a 2 cm thick layer of dust, while it is relatively rapidly destroyed in the surface layer, and that biomolecules like proteins and polynucleotides are more resistant to destruction than living biota.

Exposure of phototrophs to 548 days in low Earth orbit: microbial selection pressures in outer space and on early earth

“…Although organisms beneath the altered surface layer did not exhibit obvious alteration by bright-field microscopy, the data suggest that the detrimental effects of UV radiation can penetrate to the natural community covered by the augmented cyanobacteria. UV radiation damage could have been caused either directly to cell components such as DNA, which did not manifest itself as destruction of accessory pigments or carotenoids, or indirectly by the production of damaging radicals in the surface layer that subsequently destroyed the subsurface layers (Hansen et al, 2009).…”

On the edge of habitability and the extremes of liquidity

“…Other studies that expose micro-organisms to simulated Martian conditions do not focus on the role of brines. However, it is to be expected that both samples of Arctic permafrost (Hansen et al, 2009) and rocks with alpine lichen (de Vera et al, 2010) are subject to some brine formation in the interstices of the soil or in cracks of the rock. It is challenging to directly measure the amount of liquid brine in a biological sample mounted in a Mars simulation chamber.…”

Biological ultraviolet Dosimetry in Low Earth’s Orbit

“…On the EXPOSE-E facility during the1.5 years flight time at the samples from cosmic radiation a dose of 180 mGy was measured [34,35] Assuming a very similar cosmic radiation at the EXPOSE-R facility one can estimate for The maximal dose until saturation is less than 400 kJ/m 2 for 290 nm, while for 300 nm 1200 kJ/m 2 , thus the dimerization efficiency of the wavelength 290 nm is higher, while the wavelength 300 nm is less efficient [33]. 6 The selection was by interference band pass filters: 220BP10, 230BP10, 260BP10, 270BP10, 280BP10, 290BP10, 300BP10, 310BP10, 320BP10, where the first number denotes the wavelength of maximal transparency and the last one the band width. 2.…”

“…In the simulation experiments the dimerization and reversion efficiencies of the selected 6 short wavelength radiation were determined on uracil thin layers. In Figure 4 the effect induced by two selected wavelengths (290 nm and 300 nm) is demonstrated in dependence of the dose.…”

“…The theoretical one constructs mathematical or physical model which supports the life or analyzes the physical, chemical parameters of the planets in terms of the evolution or the interplanetary transport of life [1][2][3]. The experimental astrobiology uses possible terrestrial model of specific planets, like deserts, permafrost, simulation chambers etc [4][5][6][7][8][9]. These provide environmental parameters similar to the space and to the specific planet respectively, while the in situ measurements allow studying the life conditions directly in the specific environment [10][11][12].…”