Raman Spectroscopic and Microbial Analysis of Microbial Mat Hosted Gypsum from the Dohat Faishakh Sabkha in Qatar and its Astrobiological Implications

The discovery of gypsum (CaSO₄●2H₂O) on Mars by the NASA Mars Exploration Rover Opportunity has corroborated past models about the early composition of the Red Planet. In extreme environments, minerals, such as gypsum, which are formed through the evaporation of water, can act as a refuge for extremophilic microorganisms. After providing a refuge from desiccation, rapid temperature fluctuations, and elevated levels of UV-radiation, gypsum can preserve biomarkers by sealing them. To better understand the geobiological interactions of pigments and other biomarkers possibly encapsulated in a gypsum matrix, samples of gypsum collected from a depth of 25cm within microbial mats in the Dohat Faishakh sabkha in Qatar were examined. The Dohat Faishakh sabkha is considered an Earth analogue to past evaporitic environments on Mars due to its extremely high salinity, harsh desiccation, and intense levels of UV-radiation. The aim of this work was to holistically evaluate the buried microbial community and gypsum-hosted biomarkers to gain insight into the best practices for Raman signal detection. 16s rRNA analyses was employed to determine organisms present and their aptitude for producing biomarkers. Raman microscopic analysis was applied to prove whether any biomarkers were trapped within the gypsum matrix. We observed that gypsum formed in a layer heavily dominated by halophilic archaea (>50% total abundance) and organic matter produced by microorganisms was encapsulated resulting in distinct Raman spectra. Several types of organic molecules were identified including carotenoids, chlorophylls, scytonemin and phycobiliproteins suggesting that complex signatures were preserved in gypsum.