Abstract EANA2025-56

Understanding the formation and microbial habitability of brines on Mars remains a central question in astrobiology, not least because transient salty films formed by deliquescence may represent the most promising microhabitats for putative extant life on the Red Planet. Over the past decade, the Astrobiology Research Group at TU Berlin has systematically investigated how perchlorate and chloride brines could form under Mars-like conditions and whether microbes can adapt to their harsh physicochemical constraints. Using growth experiments (partly involving a Mars simulation chamber) and a range of analytical approaches such as scanning electron microscopy, proteomics, and metabolomics, we have tested microbial model organisms as well as species isolated from Mars-analogue environments such as Don Juan Pond, Antarctica, across varied brine chemistries and temperatures. In this presentation, I will summarize the main results of this research and provide an outlook on upcoming projects.

Our recent studies have demonstrated that the bacterial strain Planococcus halocryophilus, isolated from the Canadian High Arctic, and the halotolerant yeast Debaryomyces hansenii can tolerate perchlorate- and chloride-rich brines beyond previously known limits, effectively redefining the upper boundaries for microbial perchlorate tolerance on Mars [1-4]. Proteomic analyses of D. hansenii revealed chaotropic stress responses including cell wall remodeling and protein glycosylation [5], while Escherichia coli exposed to perchlorate-rich brines showed upregulation of DNA repair, RNA methylation, and de novo IMP biosynthesis pathways [6], indicating highly species-specific stress responses critical for survival under Mars-relevant conditions. Experiments simulating shallow subsurface environments in a Mars chamber indicated a clear microbial preference for chlorate over perchlorate brines due to lower toxicity [7]. Additionally, methanogenic archaea have been shown to produce methane in deliquescence-driven microenvironments, linking brine formation to potential methane sources detected on Mars [8]. Collectively, these findings refine the physicochemical boundaries for life under Mars-analog salt conditions, enhancing our ability to evaluate the actual habitability of transient brines.

However, open questions remain regarding the adaptive potential of microbes under multi-stress Mars conditions and the spatio-temporal availability of stable liquid brines within the Martian regolith. Looking ahead, the upcoming EXOSALT project (“Exploring non-NaCl Salts as Potential Habitats for Extraterrestrial Life”) at ZARM, University of Bremen, will take this research to the next level by including field campaigns in the Atacama Desert, Chile, where we aim to isolate halotolerant species associated with non-NaCl salts and investigate their potential to thrive under Mars-like conditions and to produce salt-specific biosignatures, facilitating life-detection experiments in future Mars missions, such as the – hopefully – upcoming ExoMars Rosalind Franklin rover.

References: [1] Heinz et al. (2018) doi:10.1089/ast.2017.1805; [2] Heinz et al. (2019) doi:10.1089/ast.2019.2069; [3] Heinz et al. (2020) doi:10.3390/life10050053; [4] Heinz et al. (2021) doi:10.3390/life11111194; [5] Heinz et al. (2022) doi:10.1111/1462-2920.16152; [6] Kloss et al. (2025) doi:10.1038/s41598-025-91562-3; [7] Fischer et al. (2024) doi:10.1038/s41598-024-62346-y; [8] Maus et al. (2020) doi:10.1038/s41598-019-56267-4.