Table1.docx

<p>Growth in sodium chloride (NaCl) is known to induce stress in non-halophilic microorganisms leading to effects on the microbial metabolism and cell structure. Microorganisms have evolved a number of adaptations, both structural and metabolic, to counteract osmotic stress. These strategies are well-understood for organisms in NaCl-rich brines such as the accumulation of certain organic solutes (known as either compatible solutes or osmolytes). Less well studied are responses to ionic environments such as sulfate-rich brines which are prevalent on Earth but can also be found on Mars. In this paper, we investigated the global metabolic response of the anaerobic bacterium Yersinia intermedia MASE-LG-1 to osmotic salt stress induced by either magnesium sulfate (MgSO₄) or NaCl at the same water activity (0.975). Using a non-targeted mass spectrometry approach, the intensity of hundreds of metabolites was measured. The compatible solutes L-asparagine and sucrose were found to be increased in both MgSO₄ and NaCl compared to the control sample, suggesting a similar osmotic response to different ionic environments. We were able to demonstrate that Yersinia intermedia MASE-LG-1 accumulated a range of other compatible solutes. However, we also found the global metabolic responses, especially with regard to amino acid metabolism and carbohydrate metabolism, to be salt-specific, thus, suggesting ion-specific regulation of specific metabolic pathways.</p

Survival of <i>Y</i>. <i>intermedia</i> MASE-LG-1 after exposure to desiccation, vacuum and Martian atmosphere.

<p>N₀: viable cells without desiccation / exposure to vacuum, N: viable cells after desiccation / exposure to vacuum (n = 3). Black: Cells were desiccated on glass slides under anoxic conditions. Light grey: Cells were desiccated on quartz discs under anoxic conditions and exposed to vacuum (10⁻⁵ Pa) within the Trex-Box. Dark grey: Cells were desiccated on quartz discs under anoxic conditions and exposed to Martian atmosphere (Mars gas at a pressure of 10⁻³ Pa) within the Trex-Box.</p

Influence of perchlorates.

<p>Influence of perchlorates on tolerance to desiccation (A) and ionizing radiation (B). N₀: Viable cells without desiccation / irradiation, N: Viable cells after desiccation / irradiation. Recovery was performed under standard cultivation conditions without perchlorate (n = 3). Asterisks denote significant difference (<i>p</i> < 0.05) to the control (survival after desiccation without perchlorates). (A) Black columns: Cells were exposed (15 min) to 0.5% perchlorate (0.5% NaClO₄ = 35.6 mM; 0.5% Ca(Cl₄)₂ = 20.9 mM; 0.5% Mg(ClO₄)₂ = 22.4 mM) before desiccation treatment (24 h, anoxic conditions). Grey columns: Cells were exposed (15 min) to 1.0% perchlorate (1.0% NaClO₄ = 71.2 mM; 1.0% Ca(Cl₄)₂ = 41.9 mM; 1.0% Mg(ClO₄)₂ = 44.8 mM) before desiccation treatment (24 h, anoxic conditions). (B) Cells were exposed (15 min) to the indicated perchlorates before treatment with ionizing radiation up to 800 Gy. Black circles: 0.5% Mg(ClO₄)₂; White circle: 1% Mg(ClO₄)₂; Black triangle: 0.5% Na(ClO₄); White triangle: 1% Na(ClO₄); Black square 0.5% Ca(ClO₄)₂; White square: 1% Ca(ClO₄)₂.</p

Overview of performed single and combined stress tests with strain MASE-LG-1.

<p>Overview of performed single and combined stress tests with strain MASE-LG-1.</p

The Trex-Box.

<p>The desiccated cells on quartz glass discs can be positioned (arrow 1) inside the open Trex-Box. The box can be connected to various pumping systems (arrow 2) (A). Closed Trex-Box is ready for exposure to combined stresses e.g. radiation and vacuum (B).</p

Survival after desiccation and radiation.

<p>Survival of <i>Y</i>. <i>intermedia</i> MASE-LG-1 after anoxic desiccation (A) and after exposure to ionizing radiation (B). N_0: Viable cells without desiccation / irradiation, N: Viable cells after desiccation / irradiation (n = 3). (A) Cells were applied on glass slides and dried under anoxic conditions up to 190 days. (B) Cells were exposed to ionizing radiation up to 1000 Gy in liquid culture medium under anoxic conditions.</p