Searching new extremophilic microbial model systems for space exploration studies – data from a large-scale transect study in the Atacama Desert

Abstract

The search for new model organisms for space exploration missions in the Atacama Desert is traditionally limited to a rather narrow strip (Yungay, Chile) which is believed to have the most arid conditions on Earth (McKay et al., 2003) thus harboring the most desiccation-resistant microorganisms. However, it is not clear whether Yungay is indeed the driest place in the Atacama, as this should be the one with the lowest soil organic carbon (SOC) stock and soil water (SW) content. Therefore we tested different soil samples from an aridity-gradient transect with comparable sites (inclination, position in the rain shadow of the coastal mountain range, approx. 100 km distance between the sites) spanning roughly 600 km in the Atacama Desert for SOC stocks and SW content. We found, that SOC stocks decreased with aridity from 25.5 to 2.1 kg m-2 cm-1, while the SW contents decreased at 5 of our sites and increased in the hyper-arid zone. To our surprise, we identified one site located 100 km north of Yungay which had substantially lower SOC stocks (1.92 kg m-2 cm-1 ± 0.73) than Yungay (2.21 kg m-2 cm-1 ± 0.75), but with 0.043 g of water per 1 g of soil ± 0.03 comparable SW contents, while Yungay has 0.043 g ± 0.06. Thus we consider this site to display different growth conditions and ecological niches as compared to Yungay and therefore as promising candidate site for the identification of new species of radiation-resistant microorganisms, as the resistance against desiccation is paired with a distinct resistance to ionizing radiation due to efficient microbial DNA repair mechanisms (Mattimore et al., 1995). Soil samples were irradiated with high doses of gamma radiation up to 25 000 Gy. Surviving colonies were cultivated on a medium favoring the growth of Deinococcus-like species and their affiliation was determined using 16sRNA-Next Generation Sequencing. Here, we evaluate the hypothesis of ecological niching even at the most hyper-arid places of our planet on grounds of our recently identified site – with implications for the search for life in hyper-arid Martian regolith in future robotic space exploration missions such as ExoMars.