A salt-loving microorganism from Earth did more than endure a months-long experiment designed around possible conditions beneath Mars. It grew in concentrated brine under low pressure, using nitrate or perchlorate in place of oxygen during respiration. The result extends research on the resilience of Earth microbes. It also raises a question for Mars exploration: Which combinations of harsh conditions can still permit biological activity?
link to open access paper https://journals.asm.org/doi/10.1128/aem.01749-26
Conclusion: We have shown that H. volcanii can actively grow under environmental and chemical conditions relevant to the present-day shallow Martian subsurface. However, this study was not designed to replicate the full thermal variability of the Martian surface or shallow subsurface, including diurnal and seasonal freeze–thaw cycles, or the complete suite of chemical conditions presently understood to exist on Mars. Rather, the objective was to determine whether active metabolism is physically possible under Mars-relevant combinations of low atmospheric pressure, high salinity, and oxidizing chemistry, provided that liquid water is available in the form of brines. Moreover, the media used in many previous low-pressure Mars simulation studies, including those employed herein, are supplemented with carbon sources and nutrients that are not representative of the current understanding of biologically available organic compounds on Mars (83).
Our future studies will investigate the capacity of halophilic and psychrophilic microorganisms to grow under conditions that more closely approximate the Amazonian/present-day Martian environment by incorporating freeze–thaw cycles, defined Mars media (94) containing Mars-relevant organic compounds (e.g., acetate) (95), and Mars regolith simulants. Moreover, future experiments would benefit from incorporating additional analytical approaches, including direct cell counts and quantitative biomass measurements, to better characterize population growth and cell-division dynamics under low-pressure conditions. Integrating transcriptomic and proteomic analyses would further enable identification of the molecular pathways involved in hypobaric tolerance, anaerobic metabolism, and adaptation to combined Mars-relevant environmental stressors.
As experimental systems increasingly approximate present-day conditions on Mars, the combined effects of low pressure, low temperature, high salinity, anoxia, radiation, and oxidizing compounds will likely reduce growth yields and metabolic rates. Sensitive, complementary, and agnostic approaches will therefore become increasingly important for detecting and distinguishing subtle biological responses under these more harmful conditions.
The results presented here do not imply that microbial life exists on Mars today. However, they add to a growing body of evidence suggesting that the shallow subsurface of Mars may retain environmental conditions capable of supporting active metabolism and extant life (83, 96–98).
