Extracellular electron transfer (EET) allows microorganisms to gain energy by linking intracellular reactions to external surfaces ranging from natural minerals to the electrodes of bioelectrochemical renewable energy technologies. In the past two decades, electrochemical techniques have been used to investigate EET in a wide range of microbes, with emphasis on dissimilatory metal-reducing bacteria, such as Shewanella oneidensis MR-1, as model organisms. However, due to the typically bulk nature of these techniques, they are unable to reveal the subpopulation variation in EET or link the observed electrochemical currents to energy gain by individual cells, thus overlooking the potentially complex spatial patterns of activity in bioelectrochemical systems. Here, to address these limitations, we use the cell membrane potential as a bioenergetic indicator of EET by S. oneidensis MR-1 cells. Using a fluorescent membrane potential indicator during in vivo single-cell-level fluorescence microscopy in a bioelectrochemical reactor, we demonstrate that membrane potential strongly correlates with EET. Increasing electrode potential and associated EET current leads to more negative membrane potential. This EET-induced membrane hyperpolarization is spatially limited to cells in contact with the electrode and within a near-electrode zone (<30 μm) where the hyperpolarization decays with increasing cell-electrode distance. The high spatial and temporal resolution of the reported technique can be used to study the single-cell-level dynamics of EET not only on electrode surfaces, but also during respiration of other solid-phase electron acceptors.

细胞外电子转移（EET）允许微生物通过将细胞内反应与外表面（从天然矿物质到生物电化学可再生能源技术的电极）联系起来来获得能量。在过去的二十年中，电化学技术已被用于研究多种微生物中的 EET，重点是异化金属还原细菌，例如Shewanella oneidensis MR-1，作为模型生物。然而，由于这些技术通常具有批量性质，它们无法揭示 EET 的亚群变化或将观察到的电化学电流与单个细胞的能量增益联系起来，从而忽略了生物电化学系统中潜在的复杂的活动空间模式。在这里，为了解决这些限制，我们使用细胞膜电位作为S. oneidensis MR-1 细胞 EET 的生物能指标。在生物电化学反应器中的体内单细胞水平荧光显微镜中使用荧光膜电位指示器，我们证明膜电位与 EET 密切相关。增加电极电位和相关的 EET 电流会导致更大的负膜电位。这种 EET 诱导的膜超极化在空间上仅限于与电极接触的细胞和近电极区域（<30 μm）内，其中超极化随着细胞电极距离的增加而衰减。所报道的技术的高空间和时间分辨率可用于研究 EET 的单细胞水平动力学，不仅在电极表面上，而且在其他固相电子受体的呼吸过程中。