Kracke Frauke, Vassilev Igor, Krömer Jens O
Centre for Microbial Electrochemical Systems, The University of Queensland, Brisbane QLD, Australia ; Advanced Water Management Centre, The University of Queensland, Brisbane QLD, Australia.
Front Microbiol. 2015 Jun 11;6:575. doi: 10.3389/fmicb.2015.00575. eCollection 2015.
Microbial electrochemical techniques describe a variety of emerging technologies that use electrode-bacteria interactions for biotechnology applications including the production of electricity, waste and wastewater treatment, bioremediation and the production of valuable products. Central in each application is the ability of the microbial catalyst to interact with external electron acceptors and/or donors and its metabolic properties that enable the combination of electron transport and carbon metabolism. And here also lies the key challenge. A wide range of microbes has been discovered to be able to exchange electrons with solid surfaces or mediators but only a few have been studied in depth. Especially electron transfer mechanisms from cathodes towards the microbial organism are poorly understood but are essential for many applications such as microbial electrosynthesis. We analyze the different electron transport chains that nature offers for organisms such as metal respiring bacteria and acetogens, but also standard biotechnological organisms currently used in bio-production. Special focus lies on the essential connection of redox and energy metabolism, which is often ignored when studying bioelectrochemical systems. The possibility of extracellular electron exchange at different points in each organism is discussed regarding required redox potentials and effect on cellular redox and energy levels. Key compounds such as electron carriers (e.g., cytochromes, ferredoxin, quinones, flavins) are identified and analyzed regarding their possible role in electrode-microbe interactions. This work summarizes our current knowledge on electron transport processes and uses a theoretical approach to predict the impact of different modes of transfer on the energy metabolism. As such it adds an important piece of fundamental understanding of microbial electron transport possibilities to the research community and will help to optimize and advance bioelectrochemical techniques.
微生物电化学技术描述了一系列新兴技术，这些技术利用电极与细菌的相互作用来进行生物技术应用，包括发电、废弃物及废水处理、生物修复以及有价值产品的生产。每种应用的核心在于微生物催化剂与外部电子受体和/或供体相互作用的能力及其代谢特性，这些特性使电子传递与碳代谢得以结合。而这也是关键挑战所在。已发现多种微生物能够与固体表面或媒介物交换电子，但仅有少数得到了深入研究。尤其是从阴极到微生物体的电子转移机制了解甚少，然而对于许多应用（如微生物电合成）而言却至关重要。我们分析了自然界为诸如金属呼吸细菌和产乙酸菌等生物体提供的不同电子传递链，同时也分析了目前用于生物生产的标准生物技术生物体的电子传递链。特别关注的是氧化还原与能量代谢的基本联系，而在研究生物电化学系统时这一点常常被忽视。针对每种生物体中不同点处细胞外电子交换的可能性，结合所需的氧化还原电位以及对细胞氧化还原和能量水平的影响进行了讨论。确定并分析了关键化合物，如电子载体（如细胞色素、铁氧化还原蛋白、醌、黄素）在电极 - 微生物相互作用中可能发挥的作用。这项工作总结了我们目前对电子传递过程的认识，并采用理论方法预测不同转移模式对能量代谢的影响。因此，它为研究界增添了对微生物电子传递可能性的重要基础理解，并将有助于优化和推进生物电化学技术。
