Perchlorate salts lower the vitrification point of Bacillus Subtilis to temperatures lower than those expected beneath the Martian south pole

• Main Authors: Gault, Stewart, Cockell, Charles, S, Fonseca, Fernanda, Passot, Stéphanie
• Other Authors: UK Centre for Astrobiology, SUPA School of Physics and Astronomy, University of Edinburgh, James Clerk Maxwell Building, Peter Guthrie Tait Road, Edinburgh, EH9 3FD, Université Paris-Saclay, INRAE, AgroParisTech, UMR SayFood, F-91120 Palaiseau, France
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2023
• Subjects: [SDU]Sciences of the Universe [physics]; South Pole; South pole
• Online Access: https://hal.science/hal-04397603

International audience The discovery of lakes beneath the Martian south pole has led to questions of theirhabitability. These lakes should be characterised by incredibly low temperatures,around -70°C, and high concentrations of eutectic compounds, such as perchloratesalts, in order to facilitate their liquid nature at such low temperatures (1,2). Previousresearch has shown that the low temperature limit for life is physically set by theonset of intracellular vitrification, which typically occurs around -23°C (3). Thissuggests that any potential life found within these lakes would be vitrified andpreserved as opposed to being biologically active. However, as perchlorate salts cangreatly depress the freezing point of water, the question arose as to whether theycould likewise reduce the point at which cells vitrify. Using differential scanningcalorimetry and fluorescence microscopy and spectroscopy, we found that Mg(ClO4)2lowered the vitrification point of Bacillus Subtilis cells in a concentration dependentfashion from 0.6M onwards. Additionally, we found that 2.5M Mg(ClO4)2 lowered thevitrification point of Bacillus Subtilis to -83°C, therefore suggesting that cells couldremain in an active, liquid-like state beneath the Martian south pole if they couldtolerate such high perchlorate concentrations alongside extremely low temperatures.These results also represent a new theoretical low temperature limit for life.AcknowledgmentsS.