Physicochemical Salt Solution Parameters Limit the Survival of Planococcus halocryophilus in Martian Cryobrines

Perchlorate-Specific Proteomic Stress Responses of Debaryomyces hansenii Could Enable Microbial Survival in Martian Brines

If life exists on Mars, it would face several challenges including the presence of perchlorates, which destabilize biomacromolecules by inducing chaotropic stress. However, little is known about perchlorate toxicity for microorganism on the cellular level. Here we present the first proteomic investigation on the perchlorate-specific stress responses of the halotolerant yeast Debaryomyces hansenii and compare these to generally known salt stress adaptations. We found that the responses to NaCl and NaClO₄ -induced stresses share many common metabolic features, e.g., signaling pathways, elevated energy metabolism, or osmolyte biosynthesis. Nevertheless, several new perchlorate-specific stress responses could be identified, such as protein glycosylation and cell wall remodulations, presumably in order to stabilize protein structures and the cell envelope. These stress responses would also be relevant for life on Mars, which - given the environmental conditions - likely developed chaotropic defense strategies such as stabilized confirmations of biomacromolecules and the formation of cell clusters. This article is protected by copyright. All rights reserved.

Anion-type modulates the effect of salt stress on saline lake bacteria

Beside sodium chloride, inland saline aquatic systems often contain other anions than chloride such as hydrogen carbonate and sulfate. Our understanding of the biological effects of salt composition diversity is limited; therefore, the aim of this study was to examine the effect of different anions on the growth of halophilic bacteria. Accordingly, the salt composition and concentration preference of 172 strains isolated from saline and soda lakes that differed in ionic composition was tested using media containing either carbonate, chloride or sulfate as anion in concentration values ranging from 0 to 0.40 mol/L. Differences in salt-type preference among bacterial strains were observed in relationship to the salt composition of the natural habitat they were isolated from indicating specific salt-type adaptation. Sodium carbonate represented the strongest selective force, while majority of strains was well-adapted to growth even at high concentrations of sodium sulfate. Salt preference was to some extent associated with taxonomy, although variations even within the same bacterial species were also identified. Our results suggest that the extent of the effect of dissolved salts in saline lakes is not limited to their concentration but the type of anion also substantially impacts the growth and survival of individual microorganisms.

Physicochemical Parameters Limiting Growth of Debaryomyces hansenii in Solutions of Hygroscopic Compounds and Their Effects on the Habitability of Martian Brines

The availability of liquid water is a prerequisite for all lifeforms on Earth. In hyperarid subzero environments like the Dry Valleys in Antarctica or the near-subsurface of Mars liquid water might be provided temporarily by hygroscopic substances that absorb water from the atmosphere and lower the freezing point of water. To evaluate the potential of hygroscopic compounds to serve as a habitat, it is necessary to explore the microbial tolerances towards these substances and their life-limiting properties. Here we present a study investigating the tolerances of the halotolerant yeast Debaryomyces hansenii to various solutes. Growth experiments were conducted via counting colony forming units (CFUs) after inoculation of a liquid growth medium containing a specific solute concentration. The lowest water activities (a_w) enabling growth were determined to be ~0.83 in glycerol and fructose-rich media. For all other solutes the growth-enabling a_w was higher, due to additional stress factors such as chaotropicity and ionic strength. Additionally, we found that the solute tolerances of D. hansenii correlate with both the eutectic freezing point depressions and the deliquescence relative humidities of the respective solutes. Our findings strongly impact our understanding of the habitability of solute-rich low a_w environments on Earth and beyond.