Bioelectrochemical system (BES) is a unique biotechnology for wastewater treatment and energy recovery, and extracellular electron transfer (EET) between microbe and electrode is the key to optimize the performance of BESs. Resazurin is an effective artificial compound that can promote EET in BESs, but the way how it transports electrons is not fully understood. In this study differential pulse voltammetry revealed that the redox potential of resorufin (RR) (intermediate of resazurin reduction, actual electron mediator) within Geobacter sulfurreducens biofilm was positively shifted by 100 mV than that of free RR, and this shift was attenuated by the mutation of outer-membrane cytochrome gene omcE but not by omcS and omcZ mutation, indicating that RR specifically interacted with OmcE. By using heterologously expressed OmcE monomers in Escherichia coli, it was found that RR bonded with OmcE monomers with a moderate intensity (dissociation constant of 720 nM), and their interaction obviously increased the content of α helix in OmcE monomers. Biomolecular analysis indicated that heme II of OmcE monomer might be the binding site for RR (binding energy of -7.01 kJ/mol), which were favorable for electron transfer within OmcE-RR complex. Comparative transcriptomics showed that RZ addition significantly upregulated the expression of omcE, periplasmic cytochrome gene ppcB, and outer-membrane genes omaB, ombB and omcB, thus, it was hypothesized that OmcE-bound RR might serve as potential electron acceptor of OmbB-OmaB-OmcB porin complex which passes electrons across outer membrane. Our work demonstrated a new pathway of artificial electron mediators in facilitating EET in Geobacter species, which may guide the application of electron mediator in improving the performance of BESs.

中文翻译：

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试卤灵与硫还原地杆菌外膜细胞色素 OmcE 的特异性相互作用：关于人工电子介质促进细胞外电子转移的新见解


生物电化学系统 （BES） 是一种独特的废水处理和能量回收生物技术，微生物和电极之间的细胞外电子转移 （EET） 是优化 BES 性能的关键。刃天青是一种有效的人工化合物，可以在 BES 中促进 EET，但它如何传输电子的方式尚不完全清楚。在本研究中，差分脉冲伏安法显示，Geobacter sulfurreducens 生物膜内试卤灵 （RR）（刃天青还原的中间体，实际电子介质）的氧化还原电位比游离 RR 的氧化还原电位正偏移 100 mV，并且这种偏移被外膜细胞色素基因 omcE 的突变减弱，而不是被 omcS 和 omcZ 突变减弱， 表明 RR 与 OmcE 有特异互。通过在大肠杆菌中使用异源表达的 OmcE 单体，发现 RR 与中等强度的 OmcE 单体键合 （解离常数为 720 nM），它们的相互作用明显增加了 OmcE 单体中 α 螺旋的含量。生物分子分析表明，OmcE 单体的血红素 II 可能是 RR 的结合位点 （结合能为 -7.01 kJ/mol），有利于 OmcE-RR 复合物内的电子转移。比较转录组学显示，RZ 添加显着上调 omcE、周质细胞色素基因 ppcB 和外膜基因 omaB、ombB 和 omcB 的表达，因此，假设 OmcE 结合的 RR 可能作为 OmbB-OmaB-OmcB 孔蛋白复合物的潜在电子受体，该复合物通过电子穿过外膜。我们的工作证明了人工电子介质在促进 Geobacter 物种 EET 中的一种新途径，这可能指导电子介质在提高 BES 性能中的应用。