Soil microbial habitats in an extreme desert Mars-analogue environment

The Atacama Desert represents one of the closest terrestrial analogues to Mars9 surface and subsurface environments. Understanding the distribution and drivers of life in the soil may thus give critical clues on how to search for biosignatures in the Martian regolith with the upcoming Mars2020 and ExoMars missions. Here, we show the result of a field experiment that combined an autonomous rover-mounted drill with ground-truth from manual sample recovery to characterize the most extreme Atacama Desert soil habitats. Distinct habitability zones were identified in soil horizons to 800mm depth in two Mars-like terrains, an evaporite-rich playa and a gravel desert pavement. Highly specialised bacterial community assembly was depth-dependent and strongly influenced by soil geochemistry linked to moisture. Colonisation was also patchy and several putatively lifeless zones that correlated with high salt content were encountered. We demonstrate a clear linkage between geochemistry, moisture and biocomplexity in Mars analogue soils, and resident bacterial communities displayed putative traits that might allow survival in the Martian regolith. We discuss implication of the findings in extreme desert geobiological systems and their scientific and operational significance for upcoming Mars missions.