Electron transfer process in microbial electrochemical technologies: The role of cell-surface exposed conductive proteins

Abstract

Electroactive microorganisms have attracted significant interest for the development of novel biotechnological systems of low ecological footprint. These can be used for the sustainable production of energy, bioremediation of metal-contaminated environments and production of added-value products. Currently, almost 100 microorganisms from the Bacterial and Archaeal domains are considered electroactive, given their ability to efficiently interact with electrodes in microbial electrochemical technologies. Cell-surface exposed conductive proteins are key players in the electron transfer between cells and electrodes. Interestingly, it seems that among the electroactive organisms identified so far, these cell-surface proteins fall into one of four groups. In this review, the different types of cell-surface conductive proteins found in electroactive organisms will be overviewed, focusing on their structural and functional properties.

Electrochemical properties of pH-dependent flavocytochrome c3 from Shewanella putrefaciens adsorbed onto unmodified and catechol-modified edge plane pyrolytic graphite electrode

“…[4][5][6][7][8][9][10][11][12][13] Most studies focus on two Gramnegative mesophilic bacteria able to transfer electrons from their respiratory metabolism to extracellular solids, namely Shewanella oneidensis MR-1 and Geobacter sulfurreducens. [14] In these model electroactive microorganisms, multiheme c-type cytochromes transfer electrons from cytoplasmic and inner-membrane oxidizing enzymes towards cell surface redox proteins that are responsible for the reduction of solid phase electron acceptors. [15,16] It is also known that electron transfer is usually coupled to proton transfer which causes acidification in the anodic biofilms and in the anolyte with deleterious consequences for the biofilm metabolism and stability.…”

Engineered living conductive biofilms as functional materials

“…The mechanisms of electron transfer in Geobacter have also been extensively investigated [11,14,59,60] and recently have proven somewhat similar to those in Shewanella, featuring several multiheme cytochromes and an outer-membrane porin which, though not homologous to those in Shewanella, appear to operate in a similar fashion-indicating the possible significance of porin-cytochrome complexes for EET across multiple species. [53,61] The barriers to successful deployment of the Mtr pathway in heterologous organisms also exist for the Geobacter pathways: multiheme cytochromes which must be correctly processed and localized. However, the ease with which E. coli, at least, expresses various multiheme cytochromes varies depending on the specific protein for reasons that are not entirely understood.…”

Strategies for the Targeted Improvement of Anodic Electron Transfer in Microbial Fuel Cells

“…Nonetheless, gram‐positive prokaryotes, e.g., those from the Clostridium genus, and eukaryotes such as fungi and green algae, have also been used successfully in MFCs , . The EET mechanisms of these organisms are divided into three types: (1) direct EET via conductive membrane‐associated proteins, (2) via the use of conductive pili structures, so‐called nanowires, and (3) the diffusion‐based indirect EET via soluble endogenous redox mediators or extracellular cytochromes (c) , , (Fig. ).…”