Egicoccus halophilus EGI 80432^T, a halotolerant bacterium isolated from a saline-alkaline soil, belongs to a member of the class Nitriliruptoria, which exhibits high adaptability to salt environments. At present, the detailed knowledge of the salinity adaptation strategies of Nitriliruptoria was limited except for one research by using comparative genomics analysis. Here, we investigated the salinity adaptation mechanism of E. halophilus EGI 80432^T by comparative physiological and transcriptomic analyses. The results of physiological analyses showed that trehalose and glutamate were accumulated by salt stress and showed the maximum at moderate salinity condition. Furthermore, the contents of histidine, threonine, proline, and ectoine were increased with increasing salt concentration. We found that both 0% and 9% NaCl conditions resulted in increased expressions of genes involved in carbohydrate and energy metabolisms, but negatively affected the Na⁺ efflux, iron, and molybdate transport. Moreover, the high salt condition led to enhancement of transcription of genes required for the synthesis of compatible solutes, e.g., glutamate, histidine, threonine, proline, and ectoine, which agree with the results of physiological analyses. The above results revealed that E. halophilus EGI 80432^T increased inorganic ions uptake and accumulated trehalose and glutamate in response to moderate salinity condition, while the salinity adaptation strategy was changed from a “salt-in-cytoplasm” strategy to a “compatible solute” strategy under high salinity condition. The findings in this study would promote further studies in salt tolerance molecular mechanism of Nitriliruptoria and provide a theoretical support for E. halophilus EGI 80432^T’s application in ecological restoration.

Key Points

• Salt stress affected gene expressions responsible for carbohydrate and energy metabolisms of E. halophilus EGI 8042^T.

• E. halophilus EGI 80432^T significantly accumulated compatible solutes under salt stress.

• E. halophilus EGI 80432^T adopted a “compatible solute” strategy to withstand high salt stress.

嗜盐大肠杆菌EGI 80432 ^T是从盐碱土壤中分离出来的一种耐盐细菌，属于Nitriliruptoria类的成员，对盐环境表现出很高的适应性。目前，除一项使用比较基因组分析的研究外，关于硝化盐分适应策略的详细知识是有限的。在这里，我们研究了嗜盐大肠杆菌EGI 80432 ^T的盐度适应机制。通过比较生理和转录组分析。生理分析结果表明，海藻糖和谷氨酸盐在盐胁迫下积累，在中等盐度条件下显示最大。此外，组氨酸，苏氨酸，脯氨酸和ectoine的含量随盐浓度的增加而增加。我们发现，0％和9％的NaCl条件都会导致参与碳水化合物和能量代谢的基因表达增加，但会对Na ⁺产生负面影响外排，铁和钼酸盐的运输。此外，高盐条件导致合成相容性溶质（例如谷氨酸，组氨酸，苏氨酸，脯氨酸和ectoine）所需的基因转录增强，这与生理分析的结果一致。上述结果表明，嗜盐大肠杆菌EGI 80432 ^T响应中度盐度条件而增加了无机离子的吸收以及海藻糖和谷氨酸的积累，而盐度适应性策略已从“盐中溶质”策略更改为“相容性溶质”高盐度条件下的策略。这项研究的结果将促进进一步研究硝态氮的耐盐分子机制，并为进一步的研究提供理论依据。E. halophilus EGI 80432 ^T在生态修复中的应用。

关键点

•盐胁迫影响了嗜盐肠球菌EGI 8042 ^T的碳水化合物和能量代谢的基因表达。

•在盐胁迫下，嗜盐肠球菌EGI 80432 ^T 大量积累了相容性溶质。

•嗜盐大肠杆菌EGI 80432 ^T 采用了“相容性溶质”策略来承受高盐胁迫。