Ethanologenic alphaproteobacterium Zymomonas mobilis has been acknowledged as a promising biofuel producer. There have been numerous efforts to engineer this species applicable for an industrial-scale bioethanol production. Although Z. mobilis is robustly resilient to certain abiotic stress such as ethanol, the species is known to be sensitive to saline stress at a mild concentration, which hampers its industrial use as an efficient biocatalyst. To overcome this issue, we implemented a laboratory adaptive evolution approach to obtain salt tolerant Z. mobilis strain. During an adaptive evolution, we biased selection by cell morphology to exclude stressed cells. The evolved strains significantly improved growth and ethanol production in the medium supplemented with 0.225 M NaCl. Furthermore, comparative metabolomics revealed that the evolved strains did not accumulate prototypical osmolytes, such as proline, to counter the stress during their growth. The sequenced genomes of the studied strains suggest that the disruption of ZZ6_1149 encoding carboxyl-terminal protease was likely responsible for the improved phenotype. The present work successfully generated strains able to grow and ferment glucose under the saline condition that severely perturbs parental strain physiology. Our approach to generate strains, cell shape-based diagnosis and selection, might be applicable to other kinds of strain engineering in Z. mobilis.

中文翻译：

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通过适应性进化产生的运动发酵单胞菌菌株的耐盐性增加。


产乙醇α变形菌运动发酵单胞菌已被公认为是一种有前途的生物燃料生产者。人们已经做出了许多努力来设计该物种以适用于工业规模的生物乙醇生产。尽管运动发酵单胞菌对某些非生物胁迫（例如乙醇）具有很强的抵抗力，但已知该物种对温和浓度的盐水胁迫敏感，这阻碍了其作为有效生物催化剂的工业用途。为了克服这个问题，我们实施了实验室适应性进化方法来获得耐盐运动发酵单胞菌菌株。在适应性进化过程中，我们通过细胞形态进行偏向选择以排除应激细胞。进化后的菌株在补充有 0.225 M NaCl 的培养基中显着改善了生长和乙醇产量。此外，比较代谢组学表明，进化后的菌株不会积累典型的渗透剂（例如脯氨酸）来对抗生长过程中的压力。研究菌株的基因组测序表明，编码羧基末端蛋白酶的 ZZ6_1149 的破坏可能是表型改善的原因。目前的工作成功地产生了能够在严重干扰亲本菌株生理机能的盐水条件下生长和发酵葡萄糖的菌株。我们产生菌株、基于细胞形状的诊断和选择的方法可能适用于运动发酵单胞菌的其他类型的菌株工程。