About this Research Topic
Electron transfer is an essential biological process for all living systems. The understanding of the electron transfer process is one of the most exciting topics for researchers in the area of microbiology. For centuries, researchers believed that the bacterial electron transfer is a purely intracellular process: the electron transportation chain is located in the inner membrane, and the electron transfer reactions proceed in the periplasm or cytoplasm of cells, while electrons are never transported across the outer membrane of the cells.
In recent years, a very unique and interesting electron transfer style termed “extracellular electron transfer (EET)” was explored in microorganisms and attracted much attention. EET is totally different from the conventional intracellular electron transfer, as the electrons were transported across the outer membrane of the cells. Two kinds of EET styles have been explored, classified based on the electron transportation direction: outwards electron transfer and inwards electron transfer. With this bidirectional bacterial EET, bacteria can exchange electrons with extracellular electron acceptors/donors by employing sophisticated EET pathways. More recently, it was found that bacteria could exchange electrons between cells with diverse EET processes. Furthermore, bidirectional EET was proved to be crucial for bacterial anaerobic metabolism and consortium function. Besides, it plays important roles in bio-driving geochemical cycling processes, including metal elements, nitrogen and carbon cycling. Therefore, the understanding of the EET mechanism is important for unveiling the mystery of bacterial metabolism, bacterial cell-cell interaction and cell-mineral interaction, which may provide new insight into bacterial living style and biogeochemical process.
More impressively, with the aid of EET, bacteria can respire with solid matters such as metal oxides, solid minerals or solid electrode, which not only greatly broadens the diversity of bacterial respiration and expands the living niche of the bacteria, but also enables the development of various novel applications. Bioelectrochemical systems including microbial fuel cells, microbial electrolysis cells, and microbial electrosynthesis systems have rapidly developed and are considered to be promising technologies for energy/resources recovery from wastewater and CO2 fixation and transformation. Bacterial electron transfer manipulation, including cell-cell electron exchange engineering, was also applied as a promising strategy for bacterial metabolism optimization. More recently, bio-hybrid systems based on bacterial EET and photoelectric effects have attracted much attention for solar fuels production, which may hold great promise for developing new pathways for sustainable fuels production. In summary, the booming of research on EET applications has already proved the power of bacterial bidirectional EET and practical applications could be expected.
This Research Topic is dedicated to the importance of bacterial bidirectional EET. We welcome original research articles, perspectives and reviews highlighting the current advances in our understanding of the EET mechanism and the progresses on EET based applications.
Keywords: Extracellular Electron Transfer, Bioelectrochemical Systems, Biogeochemistry, Wastewater Treatment, Bioelectrocatalysis