Data_Sheet_1_Spotlight on the Energy Harvest of Electroactive Microorganisms: The Impact of the Applied Anode Potential.docx

Electroactive microorganisms (EAM) harvest energy by reducing insoluble terminal electron acceptors (TEA) including electrodes via extracellular electron transfer (EET). Therefore, compared to microorganisms respiring soluble TEA, an adapted approach is required for thermodynamic analyses. In EAM, the thermodynamic frame (i.e., maximum available energy) is restricted as only a share of the energy difference between electron donor and TEA is exploited via the electron-transport chain to generate proton-motive force being subsequently utilized for ATP synthesis. However, according to a common misconception, the anode potential is suggested to co-determine the thermodynamic frame of EAM. By comparing the model organism Geobacter spp. and microorganisms respiring soluble TEA, we reason that a considerable part of the electron-transport chain of EAM performing direct EET does not contribute to the build-up of proton-motive force and thus, the anode potential does not co-determine the thermodynamic frame. Furthermore, using a modeling platform demonstrates that the influence of anode potential on energy harvest is solely a kinetic effect. When facing low anode potentials, NADH is accumulating due to a slow direct EET rate leading to a restricted exploitation of the thermodynamic frame. For anode potentials ≥ 0.2 V (vs. SHE), EET kinetics, NAD+/NADH ratio as well as exploitation of the thermodynamic frame are maximized, and a further potential increase does not result in higher energy harvest. Considering the limited influence of the anode potential on energy harvest of EAM is a prerequisite to improve thermodynamic analyses, microbial resource mining, and to transfer microbial electrochemical technologies (MET) into practice.

电活性微生物（EAM）通过跨细胞电子转移（EET）过程，将不溶性末端电子受体（TEA），包括电极，还原以获取能量。因此，相较于呼吸可溶性TEA的微生物，EAM的热力学分析需要采取一种适应性策略。在EAM中，热力学框架（即最大可用能量）受到限制，因为只有电子供体与TEA之间的能量差的一部分，通过电子传递链被利用来产生质子驱动力，随后被用于ATP的合成。然而，根据一种普遍的误解，阳极电位被建议共同决定EAM的热力学框架。通过比较模式生物Geobacter spp.和呼吸可溶性TEA的微生物，我们推断，EAM电子传递链中相当一部分执行直接EET的环节，并不对质子驱动力的发展作出贡献，因此，阳极电位并不共同决定热力学框架。此外，利用建模平台表明，阳极电位对能量收获的影响仅是动力学效应。当面临低阳极电位时，由于直接EET速率缓慢，NADH的积累导致热力学框架的利用受限。对于阳极电位≥0.2 V（相对于标准氢电极，SHE），EET动力学、NAD+/NADH比例以及热力学框架的利用达到最大化，进一步增加电位并不会导致更高的能量收获。考虑到阳极电位对EAM能量收获的影响有限，这是改善热力学分析、微生物资源开采以及将微生物电化学技术（MET）应用于实践的先决条件。