During mixed‐acid fermentation, Escherichia coli transports succinate mainly via transporters of the Dcu family. Here, we analyze the influence of Dcu transporters on hydrogenase (Hyd) and fermentative formate dehydrogenase (FDH‐H) activities and how this is affected by external pH and carbon source. Using selected dcu mutations, it was shown that Dcu carriers mainly affect Hyd and FDH‐H activities during glycerol but not glucose fermentation at acidic pH. During glycerol fermentation at pH 5.5, inactivation of either one or all Dcu carriers increased total Hyd activity by 60% compared with wild type. Under the same growth conditions, a dcuACBD mutant had a twofold higher FDH‐H activity. When glucose was fermented in dcuD single mutant at pH 5.5, the FDH‐H activity was also increased twofold compared with wild type. Interestingly, in dcuD or dcuACBD mutants at pH 7.5, Hyd activity was lowered by 20%. Taken together, it can be concluded that during glucose fermentation at pH 7.5, lack of DcuD affects Hyd enzyme activity, but at pH 5.5, it has a stronger effect on FDH‐H activity. During glycerol fermentation, lack of Dcu carriers increased Hyd and FDH‐H activities as revealed at pH 5.5. The results suggest that impairing Dcu transport function increases intracellular formate levels and thus affects H2 cycling and proton‐motive force generation.

中文翻译：

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C4-Dcu转运蛋白对固定相发酵大肠杆菌氢化酶和甲酸脱氢酶活性的影响

在混酸发酵过程中，大肠杆菌主要通过 Dcu 家族的转运蛋白转运琥珀酸。在这里，我们分析了 Dcu 转运蛋白对氢化酶 (Hyd) 和发酵甲酸脱氢酶 (FDH-H) 活性的影响，以及这如何受外部 pH 值和碳源的影响。使用选定的 dcu 突变，表明 Dcu 载体主要影响甘油期间的 Hyd 和 FDH-H 活性，但不影响酸性 pH 下的葡萄糖发酵。在 pH 5.5 的甘油发酵过程中，与野生型相比，一种或所有 Dcu 载体的失活使总 Hyd 活性增加了 60%。在相同的生长条件下，dcuACBD 突变体的 FDH-H 活性高两倍。当葡萄糖在 pH 5.5 的 dcuD 单突变体中发酵时，与野生型相比，FDH-H 活性也增加了两倍。有趣的是，在 pH 7.5 的 dcuD 或 dcuACBD 突变体中，Hyd 活性降低了 20%。综上所述，可以得出结论，在 pH 7.5 的葡萄糖发酵过程中，DcuD 的缺乏会影响 Hyd 酶活性，但在 pH 5.5 时，它对 FDH-H 活性的影响更大。在甘油发酵过程中，缺乏 Dcu 载体会增加 Hyd 和 FDH-H 活性，如 pH 5.5 所示。结果表明，损害 Dcu 转运功能会增加细胞内甲酸水平，从而影响 H2 循环和质子动力产生。如 pH 5.5 所示，缺乏 Dcu 载体增加了 Hyd 和 FDH-H 活性。结果表明，损害 Dcu 转运功能会增加细胞内甲酸水平，从而影响 H2 循环和质子动力产生。如 pH 5.5 所示，缺乏 Dcu 载体增加了 Hyd 和 FDH-H 活性。结果表明，损害 Dcu 转运功能会增加细胞内甲酸水平，从而影响 H2 循环和质子动力产生。