Effect of saltation and abraded silicates on the survival of bacteria on Mars
Kai Finster  1@  , Per Nørnberg  2  , Svend Knack-Jensen  3  , Ebbe Bak, Ralf Moeller  4  
1 : Stellar Astrophysics Centre [Aarhus]
Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark -  Denmark
2 : Aarhus University, Department of Bioscience
Ny Munkegade 116 8000 Aarhus C -  Denmark
3 : Aarhus University; Department of Chemistry
Langelandsgade 8000 Aarhus C -  Denmark
4 : DLR Institute of Aerospace Medicine
Köln -  Germany

The Martian surface is a hostile environment for life, as it is characterized by low water availability, low atmospheric pressure and high UV and ionizing radiation. Furthermore, the hostile surface conditions are amplified by processes as wind-driven saltation that leads to abrasion of silicates with a production or reactive surface sites and triboelectric charging, a release of electrical discharges with a concomitant production of reactive oxygen species. While the effects of low water availability, low pressure and radiation have been extensively studied in relation to the habitability of the Martian surface, the risk of forward contamination and the preservation of organic biosignatures, the effects or wind-driven saltation have hitherto been ignored. In this study, we have investigated the effect of exposure of bacteria to wind-abraded silicates and direct exposure to wind-driven saltation on Mars on their viability in controlled laboratory simulation experiments. Wind-driven saltation was simulated by tumbling mineral samples in a Mars-like atmosphere in sealed quartz ampoules. The effects on bacteria survival and structure were evaluated by colony forming unit counts in combination with scanning electron microscopy, quantitative PCR and life/dead-staining with flow cytometry. The viability of vegetative cells of P. putida, B. subtilis and D. radiodurans in aqueous suspension were reduced by more than 99% by exposure to abraded basalt, while survival of B. subtilis endospores was unaffected. Experiments with several B. subtilis mutants lacking different components of their spore coat were likewise highly resistant to the exposure to abraded basalt, which indicates that the resistance of spores is not associated with any specific spore coat component. We found a slightly reduced effect of abraded quartz and we suggest that the stress effect of abraded silicates is induced by a production of reactive oxygen species and hydroxyl radicals produced by Fenton-like reactions in the presence of transition metals. Direct exposure to simulated saltation had a dramatic effect on the survival of both D. radiodurans cells and B. subtilis spore with only about 10% survival after one hour of simulated saltation for B. subtilis spores. The high susceptibility of the usually multi-resistant D. radiodurans cells and B. sublitis spores to the effect of wind-driven saltation indicates that wind abraded silicates as well as direct exposure to saltation represent a considerably stress for microorganisms at the Martian surface, which may have limited the chance the origin of indigenous life, could limit the risk of forward contamination and may have degraded potential organic biosignatures.

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