Characterization of stress tolerance and metabolic capabilities of acidophilic iron-sulfur-transforming bacteria and their relevance to Mars

Abstract

In the last decades, our neighboring planet Mars has received much attention as one of the most promising targets close to Earth on which life may have developed in the past or might even exist at present. Recent NASA and ESA missions have provided detailed information on the physical and geochemical environment of Mars that can help to identify potential habitats and organisms that could be able to grow with the energy sources present on the planet. Due to the abundance of iron and sulfur minerals on Mars, iron-sulfur transforming microorganisms are considered likely models for putative Martian life forms (e.g. Amils et al. 2007; Fernández-Remolar et al. 2005; Nixon et al. 2012). For this study, two species of acidophilic iron-sulfur bacteria were chosen: the chemolithoautotrophic Acidithiobacillus ferrooxidans and the spore-forming Sulfobacillus thermosulfidooxidans. The goal of this thesis was to study their metabolic capacities, especially regarding the ability to grow with in situ resources that could be expected on Mars, and their tolerance to environmental stress conditions. A subsurface environment was assumed as the most likely habitat in these experiments, because it has a higher probability for liquid water, can provide different sources of energy for lithotrophic metabolism, and afford protection from the harsh surface physical conditions.