Motivated by an interest in understanding the habitability of aqueous environments on Earth and in extraterrestrial settings, this study investigated the influence of ions in an artificial sodium–magnesium–sulfate–chloride ion system on the growth parameters (lag phase, growth rate, and final cell concentration) of bacteria. These four ions, in different combinations, are key components of many aqueous environments on Earth and elsewhere. We investigated non-halophilic bacteria deliberately to remove the bias of prior adaptations to high concentrations of selected ions so that we could compare the effects of different ions. We tested the hypothesis that water activity determined the growth parameters independent of the ion types. Neither water activity or ionic strength alone could predict growth. However, when ionic strengths were matched, many differences in growth parameters could be explained by the water activity. We suggest that species-specific effects (caused by differences in biochemical and physiological influences), the role of individual ions in cellular processes, and potentially the chaotropicity and kosmotropicity of solutions influenced the growth. Our data show that although extreme combinations of these ions allow for general predictions on the habitability of extraterrestrial aqueous environments, a complex interplay of ionic effects influences the growth and thus the adaptations required for given ion combinations. The data also show that an accurate quantification of the habitability of ocean worlds, such as Europa and Enceladus, can only be made when samples are obtained from these water bodies and the ion combinations are determined.

中文翻译：

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钠-镁-硫酸盐-氯化物离子系统中非嗜盐细菌的生长：阐明陆地和陆地外水环境中离子相互作用的复杂性。

出于对了解地球上和水外环境中水环境的可居住性的兴趣的动机，本研究调查了人工钠-镁-硫酸盐-氯化物离子系统中离子对生长参数（滞后相，生长速率和最终浓度）的影响。细胞浓度）的细菌。这四种离子以不同的组合形式是地球和其他地方许多水环境的关键成分。我们特意研究了非嗜盐细菌，以消除先前对高浓度选定离子的适应性偏差，以便我们可以比较不同离子的影响。我们检验了水活度决定生长参数与离子类型无关的假设。水分活度或离子强度都不能单独预测生长。但是，当离子强度匹配时，水分活度可以解释许多生长参数的差异。我们建议特定物种的影响（由生化和生理影响的差异引起），单个离子在细胞过程中的作用以及溶液的离液性和同质性可能影响生长。我们的数据表明，尽管这些离子的极端组合允许对地外水环境的适宜性进行一般性预测，但离子效应的复杂相互作用会影响生长，因此会影响给定离子组合所需的适应性。数据还表明，仅当从这些水体中获取样品并确定离子组合时，才能对欧罗巴和土卫二等海洋世界的可居住性进行准确量化。