Ethanol-type fermentation, one of the fermentation types in mixed cultures of acidogenesis with obvious advantages such as low pH tolerance and high efficiency of H2 production, has attracted widespread attentions. pH level greatly influences the establishment of the fermentation of carbohydrate acidogenesis by shaping community assembly and the metabolic activity of keystone populations. To explore the adaptation mechanisms of ethanol-type fermentation to low pH, we report the effects of initial pH on the physiological metabolism and transcriptomes of Ethanoligenens harbinense—a representative species of ethanol-type fermentation. Different initial pH levels significantly changed the cell growth and fermentation products of E. harbinense. Using transcriptomic analysis, we identified and functionally categorized 1753 differentially expressed genes (DEGs). By mining information on metabolic pathways, we probed the transcriptional regulation of ethanol–H2 metabolism relating to pH responses. Multiple pathways of E. harbinense were co-regulated by changing gene expression patterns. Low initial pH down-regulated the expression of cell growth- and acidogenesis-related genes but did not affect the expression of H2 evolution-related hydrogenase and ferredoxin genes. High pH down-regulated the expression of H2 evolution- and acidogenesis-related genes. Multiple resistance mechanisms, including chemotaxis, the phosphotransferase system (PTS), and the antioxidant system, were regulated at the transcriptional level under pH stress. Ethanoligenens adapted to low pH by regulating the gene expression networks of cell growth, basic metabolism, chemotaxis and resistance but not H2 evolution-related genes. Regulation based on pH shifts can represent an important approach to establish and enhance ethanol-type fermentation. The complete gene expression network of ethanol fermentative bacteria for pH response provides valuable insights into the acidogenic fermentation, and offers an effective regulation strategy for the sustainable energy recovery from wastewater and solid waste.

中文翻译：

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基于 Ethanoligenens harbinense 转录组分析的不同 pH 条件下乙醇型厌氧酸化发酵的代谢调控。

乙醇型发酵是产酸混合培养中的发酵类型之一，具有耐pH低、产氢效率高等明显优势，受到广泛关注。pH 水平通过塑造群落组装和关键种群的代谢活动极大地影响碳水化合物酸生成发酵的建立。为了探索乙醇型发酵对低 pH 值的适应机制，我们报告了初始 pH 值对乙醇型发酵的代表性物种 Ethanoligenens harbinense 生理代谢和转录组的影响。不同的初始pH值显着改变了哈氏大肠杆菌的细胞生长和发酵产物。使用转录组分析，我们鉴定了 1753 个差异表达基因（DEG）并对其进行了功能分类。通过挖掘有关代谢途径的信息，我们探讨了与 pH 反应相关的乙醇-H2 代谢的转录调控。通过改变基因表达模式共同调节 E. harbinense 的多种途径。低初始 pH 值下调细胞生长和酸生成相关基因的表达，但不影响 H2 进化相关氢化酶和铁氧还蛋白基因的表达。高 pH 值下调 H2 进化和酸生成相关基因的表达。多种抗性机制，包括趋化性、磷酸转移酶系统 (PTS) 和抗氧化系统，在 pH 胁迫下在转录水平上受到调节。Etholigenens 通过调节细胞生长的基因表达网络来适应低 pH 值，基本代谢、趋化性和抗性，但不是 H2 进化相关基因。基于 pH 变化的调节可以代表建立和增强乙醇型发酵的重要方法。乙醇发酵菌对 pH 响应的完整基因表达网络为产酸发酵提供了有价值的见解，并为从废水和固体废物中可持续回收能量提供了有效的调控策略。