Investigating potential Martian habitats: survival of the halotolerant yeast Debaryomyces hansenii in deliquescence-driven brines

Abstract Mars, one of the most Earth-like celestial bodies in the Solar System, is a key focus in the search for extraterrestrial life. However, pure liquid water – essential for life as we know it – is unstable on its surface today due to low pressure and frigid conditions. Concentrated salt solutions (brines) may form through the deliquescence of hygroscopic salts like chlorates and perchlorates detected on Mars, offering a potential water source for hypothetical halotolerant organisms due to the brines’ lower freezing point and reduced vapour pressure. This study simulates brine formation on Mars using a methodical setup. Martian global regolith simulant MGS-1 was either supplemented with hygroscopic salts such as sodium chloride (NaCl), sodium chlorate (NaClO 3 ), sodium perchlorate (NaClO 4 ) or used without the addition of salts as a control. Samples were inoculated with the halotolerant yeast Debaryomyces hansenii , chosen for its high (per)chlorate tolerance. Desiccated samples were transferred to an environment with constant relative humidity (98%), allowing the salts to absorb water from the atmosphere through deliquescence. The study examined the survival of D. hansenii after desiccation and its ability to grow using water absorbed through deliquescence. The results revealed that D. hansenii survived the desiccation in samples containing NaClO 3 , NaCl or no additional salt and grew in the control samples as well as in the deliquescent-driven NaClO 3 and NaCl brines. No survival was observed in samples containing NaClO 4 after the desiccation step. These findings suggest that Mars could potentially harbour life in specific niches where deliquescent brines form, specifically in NaCl or NaClO 3 rich areas. NaClO 4 , at least for the yeast tested in this study, is too toxic to support survival or growth in deliquescene-driven habitats.