We present the hypothesis that microorganisms can change the freezing/melting curve of cold salty solutions by protein expression, as it is known that proteins can affect the liquid-to-ice transition, an ability that could be of ecological advantage for organisms on Earth and on Mars. We tested our hypothesis by identifying a suitable candidate, the well-known psycrophile and halotolerant bacteria Rhodococcus sp. JG3, and analyzing its response in culture conditions that included specific hygroscopic salts relevant to Mars—that is, highly concentrated magnesium perchlorate solutions of 20 wt % and 50 wt % Mg(ClO₄)₂ at both end members of the eutectic concentration (44 wt %)—and subfreezing temperatures (263 K and 253 K). Using a combination of techniques of molecular microbiology and aqueous geochemistry, we evaluated the potential roles of proteins over- or underexpressed as important players in different mechanisms for the adaptability of life to cold environments. We recorded the changes observed by micro-differential scanning calorimetry. Unfortunately, Rhodococcus sp. JG3 did not show our hypothesized effect on the melting characteristics of cold Mg-perchlorate solutions. However, the question remains as to whether our novel hypothesis that halophilic/psychrophilic bacteria or archaea can alter the freezing/melting curve of salt solutions could be validated. The null result obtained after analyzing just one case lays the foundation to continue the search for proteins produced by microorganisms that thrive in very cold, high-saline solutions, which would involve testing different microorganisms with different salt components. The immediate implications for the habitability of Mars are discussed.

中文翻译：

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嗜盐和嗜冷微生物可以改变冷盐溶液的冷冻/融化曲线吗？对火星宜居性的影响。


我们提出这样的假设：微生物可以通过蛋白质表达改变冷盐溶液的冷冻/融化曲线，因为众所周知，蛋白质可以影响液体到冰的转变，这种能力可能对地球上的生物体具有生态优势，并且在火星上。我们通过确定合适的候选者（著名的嗜冷耐盐细菌红球菌属）来检验我们的假设。 JG3，并分析其在培养条件下的响应，其中包括与火星相关的特定吸湿盐，即共晶浓度两端成员均含有 20 wt% 和 50 wt% Mg(ClO ₄ ) ₂的高浓度高氯酸镁溶液 (44 wt %)——以及低于冰点的温度（263 K 和 253 K）。结合分子微生物学和水地球化学技术，我们评估了过度表达或表达不足的蛋白质在生命适应寒冷环境的不同机制中作为重要参与者的潜在作用。我们记录了微差示扫描量热法观察到的变化。不幸的是，红球菌属。 JG3 没有显示出我们假设的对冷高氯酸镁溶液熔化特性的影响。然而，问题仍然是我们的新假设是否可以得到验证，即嗜盐/嗜冷细菌或古细菌可以改变盐溶液的冷冻/融化曲线。仅分析一个案例后获得的无效结果为继续寻找在极冷、高盐溶液中繁殖的微生物产生的蛋白质奠定了基础，这将涉及用不同的盐成分测试不同的微生物。讨论了对火星宜居性的直接影响。