Monitoring the electrochemical response of anode respiring bacteria (ARB) helps elucidate the fundamental processes of anode respiration and their rate limitations. Understanding these limitations provides insights on how ARB create the complex interfacing of biochemical metabolic processes with insoluble electron acceptors and electronics. In this study, anode biofilms of the thermophilic (60 °C) Gram-positive ARB Thermincola ferriacetica were studied to determine the presence of a proton-dependent electron transfer response. The effects of pH, the presence of an electron donor (acetate), and biofilm growth were varied to determine their influence on the electrochemical midpoint potential ( EKA) and formal redox potential ( E°') under nonturnover conditions. The EKA and E°' are associated with an enzymatic process within ARB's metabolism that controls the rate and energetic state of their respiration. Results for all conditions indicate that pH was the major contributor to altering the energetics of T. ferriacetica anode biofilms. Electrochemical responses measured in the absence of an electron donor and with a minimal proton gradient within the anode biofilms resulted in a 48 ± 7 mV/pH unit shift in the E°', suggesting a proton-dependent rate-limiting process. Given the limited energy available for anode respiration (<200 mV when using acetate as electron donor), our results provide a new perspective in understanding proton-transport limitations in ARB biofilms, one in which ARB are thermodynamically limited by pH gradients. Since the anode biofilms of all ARB that perform direct extracellular electron transfer (EET) investigated thus far exhibit an n = 1 Nernstian behavior, and because this behavior is affected by changes in pH, we hypothesize that the Nernstian response is associated with membrane proteins responsible for proton translocation. Finally, this study shows that the EKA and E°' are a function of pH within the physiological range of ARB, and thus, given the significant effect pH has on this parameter, we recommend reporting the EKA and E°' of ARB biofilms at a specific bulk pH.

中文翻译：

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Thermincola ferriaceta 阳极生物膜的 pH 依赖性表明质子依赖性电化学响应

监测阳极呼吸细菌 (ARB) 的电化学响应有助于阐明阳极呼吸的基本过程及其速率限制。了解这些限制有助于深入了解 ARB 如何创建生化代谢过程与不溶性电子受体和电子设备的复杂接口。在这项研究中，研究了嗜热 (60 °C) 革兰氏阳性 ARB Thermincola ferriaceta 的阳极生物膜，以确定质子依赖性电子转移响应的存在。pH 值、电子供体（醋酸盐）的存在和生物膜生长的影响各不相同，以确定它们在非周转条件下对电化学中点电位 (EKA) 和正式氧化还原电位 (E°') 的影响。EKA 和 E°' 与 ARB' 内的酶促过程相关 控制呼吸速率和能量状态的新陈代谢。所有条件的结果表明 pH 值是改变 T. ferriaceta 阳极生物膜能量学的主要因素。在没有电子供体且阳极生物膜内质子梯度最小的情况下测量的电化学反应导致 E°' 中的 48 ± 7 mV/pH 单位偏移，表明存在质子依赖性限速过程。鉴于可用于阳极呼吸的能量有限（使用醋酸盐作为电子供体时<200 mV），我们的结果为理解 ARB 生物膜中的质子传输限制提供了新的视角，其中 ARB 在热力学上受 pH 梯度的限制。由于迄今为止研究的所有执行直接细胞外电子转移 (EET) 的 ARB 的阳极生物膜都表现出 n = 1 能斯脱行为，并且由于这种行为受 pH 值变化的影响，我们假设能斯脱反应与负责的膜蛋白有关用于质子易位。最后，本研究表明 EKA 和 E°' 是 ARB 生理范围内 pH 值的函数，因此，鉴于 pH 值对该参数有显着影响，我们建议报告 ARB 生物膜的 EKA 和 E°'特定的体积 pH 值。