The sugar phosphotransferase system (PTS) is an essential energy-saving mechanism, particularly under anaerobic conditions. Since the PTS consumes equimolar phosphoenolpyruvate to phosphorylate each molecule of internalized glucose in the process of pyruvate generation, its absence can adversely affect the mixed acid fermentation profile and cell growth under anaerobic conditions. In this study, we report that the ΔptsG mutant cells of Escherichia coli K-12 strain exhibited inefficient glucose utilization, produced a significant amount of succinate, and exhibited a low growth rate. However, cells adapted soon after and started to grow rapidly in the same batch culture. As a result, the adapted ΔptsG cells showed the same mixed acid fermentation profiles as the wild-type cells, which was attributed to the mutation of the mlc gene, a repressor of the D-mannose PTS, another transporter for D-glucose. Similar adaptations were observed in the cells with ΔptsGΔmanX and the cells with ΔptsI that resulted in the production of a substantial amount of succinate and fast growth rate. The genome sequencing showed the presence of null mutations in the exuR gene, which encodes a modulator of exuT-encoded non-PTS sugar transporter, in adapted ΔptsGΔmanX and ΔptsI strains. Results from the RT-qPCR analysis and genetic test confirmed that the enhanced expression of ExuT, a non-PTS sugar transporter, was responsible for the uptake of D-glucose, increased succinate production, and fast growth of adapted cells. In conclusion, our study showed that the regulatory network of sugar transporters can be modulated by short-term adaptation and that downstream metabolic flux could be significantly determined by the choice of sugar transporters.

中文翻译：

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短期适应通过激活ExuT（一种大肠杆菌中的新型D-葡萄糖转运蛋白）将厌氧代谢通量调节为琥珀酸。

糖磷酸转移酶系统（PTS）是必不可少的节能机制，尤其是在厌氧条件下。由于PTS在丙酮酸生成过程中消耗等摩尔的磷酸烯醇丙酮酸来磷酸化每个内在化的葡萄糖分子，因此PTS的缺失会不利地影响混合酸的发酵特性和厌氧条件下的细胞生长。在这项研究中，我们报告了大肠杆菌K-12菌株的ΔptsG突变细胞表现出低效的葡萄糖利用，产生了大量的琥珀酸盐，并且表现出较低的生长速率。然而，细胞很快适应并开始在同一批培养中快速生长。结果，适应的ΔptsG细胞显示出与野生型细胞相同的混合酸发酵曲线，这归因于mlc基因的突变，D-甘露糖PTS的阻遏物，D-葡萄糖的另一种转运蛋白。在具有ΔptsGΔmanX的细胞和具有ΔptsI的细胞中观察到相似的适应，导致大量琥珀酸的产生和快速生长。基因组测序表明，在适应的ΔptsGΔmanX和ΔptsI菌株中，exuR基因中存在无效突变，该基因编码exuT编码的非PTS糖转运蛋白的调节剂。RT-qPCR分析和基因测试的结果证实，非PTS糖转运蛋白ExuT的表达增强与D-葡萄糖的摄取，琥珀酸产量的增加以及适应细胞的快速生长有关。结论，