An endogenous homoethanol pathway (glucose/1.2 xylose => 2 pyruvate => 2 ethanol) was previously engineered in Escherichia coli SZ410 via eliminating acid-producing pathways and anaerobic expression of the pyruvate dehydrogenase complex (aceEF-lpd operon). This ethanologenic derivative was subsequently engineered through adaptive evolution and partial deletion of the RNase G, resulting in an improved strain of E. coli RM10 for ethanol production using C6 and C5 sugars. Nevertheless, compared to the ethanol tolerance and/or ethanol titer achieved by industrial yeast, further incremental improvement of RM10 was needed for ethanol production using cellulosic biomass derived C6 and C5 sugars. In this study, the role of aldB gene (encoding for acetaldehyde dehydrogenase, AldB, which oxidizes acetaldehyde to acetic acid) was evaluated for ethanol/acetaldehyde tolerance and xylose fermentation by RM10. Deletion of aldB gene decreased ethanol tolerance, fermentative cell growth and ethanol production from xylose; while overexpression of aldB gene improved fermentative cell growth, and increased ethanol production from xylose. The improvement is likely attributed to preventing acetaldehyde accumulation (a toxic intermediate of homoethanol pathway) via AldB catalyzed oxidation.

中文翻译：

---

乙醛脱氢酶 (aldB) 的表达提高了产乙醇大肠杆菌 RM10 从木糖中产生的乙醇

先前通过消除产酸途径和丙酮酸脱氢酶复合物（aceEF-lpd 操纵子）的厌氧表达，在大肠杆菌 SZ410 中设计了内源性高乙醇途径（葡萄糖/1.2 木糖 => 2 丙酮酸 => 2 乙醇）。这种产乙醇衍生物随后通过适应性进化和 RNase G 的部分缺失进行工程改造，从而产生了一种改良的大肠杆菌 RM10 菌株，用于使用 C6 和 C5 糖生产乙醇。然而，与工业酵母实现的乙醇耐受性和/或乙醇滴度相比，使用纤维素生物质衍生的 C6 和 C5 糖生产乙醇需要进一步提高 RM10。在本研究中，aldB 基因（编码乙醛脱氢酶，AldB，将乙醛氧化成乙酸）通过 RM10 评估乙醇/乙醛耐受性和木糖发酵。aldB 基因的缺失降低了乙醇耐受性、发酵细胞生长和木糖乙醇产量；而 aldB 基因的过表达改善了发酵细胞的生长，并增加了木糖的乙醇产量。这种改进可能归因于通过 AldB 催化氧化防止乙醛积累（高乙醇途径的一种有毒中间体）。