The Microbial Communities of Sulfate-Rich Hypersaline Mars Analogue Environments

Early Mars’s surface is proposed to have hosted habitable environments with liquid water, energy sources, and bio-essential elements. The Mars Science Laboratory Curiosity rover has identified Gale crater as an ancient habitable environment that hosted a circumneutral hyposaline lake. Geological evidence suggests Gale was temporally and spatially heterogenous, with a deposition of sulfates under evapo-concentration conditions proposed across Gale’s history. In this thesis, four desiccated sulfate-rich hypersaline lagoons in the La Mancha region in Spain were studied as analogue environments to sulfate-rich deposits at Gale crater. Geochemical characterisation showed that the sediments and salt crusts of the four study sites (Laguna de las Yeguas, Laguna Grande (Quero), Laguna de Pena Hueca, and Laguna del Longar) were rich in sulfate minerals but with differences in their chemical composition. 16S rRNA gene amplicon sequencing showed that the microbiomes of the lagoons were rich in halophiles, with beta diversity analysis identifying inter-site compositional differences. The metabolic potential of the microbiomes was analysed via shotgun metagenome sequencing. Reconstruction of metagenome-assembled genomes (MAGs) and quality filtering yielded 37 high and medium quality MAGs. Screening for genes involved in biogeochemical cycling showed the potential for dissimilatory sulfur and nitrogen metabolisms, and the utilisation of hydrogen, and one carbon compounds as electron donors. The effect of physicochemical parameters on the microbial ecology of the lagoons was elucidated via statistical and ordination analysis and ecological null modelling, which revealed that the communities of Laguna de Pena Hueca were influenced by niche-imposed selection, whereas the microbiomes of the other sites were influenced by stochastic processes. The findings of this thesis significantly expand our knowledge of the geochemical environment and the microbial ecology of four lagoons in the La Mancha region in Spain, provide evidence that Laguna de Pena Hueca might be aridifying, and showcases the use of ecological modelling in astrobiology.