The halophilic bacterium Halomonas elongata is an industrially important strain for ectoine production, with high value and intense research focus. While existing studies primarily delve into the adaptive mechanisms of this bacterium under fixed salt concentrations, there is a notable dearth of attention regarding its response to fluctuating saline environments. Consequently, the stress response of H. elongata to salt shock remains inadequately understood. This study investigated the stress response mechanism of H. elongata when exposed to NaCl shock at short- and long-time scales. Results showed that NaCl shock induced two major stresses, namely osmotic stress and oxidative stress. In response to the former, within the cell’s tolerable range (1–8% NaCl shock), H. elongata urgently balanced the surging osmotic pressure by uptaking sodium and potassium ions and augmenting intracellular amino acid pools, particularly glutamate and glutamine. However, ectoine content started to increase until 20 min post-shock, rapidly becoming the dominant osmoprotectant, and reaching the maximum productivity (1450 ± 99 mg/L/h). Transcriptomic data also confirmed the delayed response in ectoine biosynthesis, and we speculate that this might be attributed to an intracellular energy crisis caused by NaCl shock. In response to oxidative stress, transcription factor cysB was significantly upregulated, positively regulating the sulfur metabolism and cysteine biosynthesis. Furthermore, the upregulation of the crucial peroxidase gene (HELO_RS18165) and the simultaneous enhancement of peroxidase (POD) and catalase (CAT) activities collectively constitute the antioxidant defense in H. elongata following shock. When exceeding the tolerance threshold of H. elongata (1–13% NaCl shock), the sustained compromised energy status, resulting from the pronounced inhibition of the respiratory chain and ATP synthase, may be a crucial factor leading to the stagnation of both cell growth and ectoine biosynthesis. This study conducted a comprehensive analysis of H. elongata’s stress response to NaCl shock at multiple scales. It extends the understanding of stress response of halophilic bacteria to NaCl shock and provides promising theoretical insights to guide future improvements in optimizing industrial ectoine production.

中文翻译：

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长盐单胞菌对 NaCl 休克应激反应的时间动态：生理、代谢组学和转录组学见解

嗜盐细菌延长盐单胞菌是工业上重要的四氢嘧啶生产菌株，具有很高的价值和研究热点。虽然现有的研究主要深入研究这种细菌在固定盐浓度下的适应机制，但对其对波动的盐环境的响应却明显缺乏关注。因此，H. elongata 对盐休克的应激反应仍知之甚少。本研究研究了 H. elongata 在短期和长期暴露于 NaCl 冲击时的应激反应机制。结果表明，氯化钠休克诱发两种主要应激，即渗透应激和氧化应激。针对前者，在细胞的耐受范围（1-8% NaCl 冲击）内，H. elongata 通过摄取钠离子和钾离子并增加细胞内氨基酸库（特别是谷氨酸和谷氨酰胺）来紧急平衡激增的渗透压。然而，直到休克后20分钟，四氢嘧啶含量开始增加，迅速成为主要的渗透保护剂，并达到最大生产率（1450±99mg/L/h）。转录组数据也证实了四氢嘧啶生物合成的延迟反应，我们推测这可能归因于氯化钠休克引起的细胞内能量危机。为了应对氧化应激，转录因子 cysB 显着上调，积极调节硫代谢和半胱氨酸生物合成。此外，关键的过氧化物酶基因（HELO_RS18165）的上调以及过氧化物酶（POD）和过氧化氢酶（CAT）活性的同时增强共同构成了H. elongata在休克后的抗氧化防御。当超过 H. elongata 的耐受阈值（1-13% NaCl 冲击）时，由于呼吸链和 ATP 合成酶的显着抑制而导致持续受损的能量状态，可能是导致细胞生长停滞的关键因素和四氢嘧啶生物合成。本研究对H. elongata对NaCl冲击的应激反应进行了多尺度的综合分析。它扩展了对嗜盐细菌对氯化钠冲击的应激反应的理解，并为指导未来优化工业四氢嘧啶生产的改进提供了有前景的理论见解。