Redox Mediators in Microbial Electrochemical Systems

Abstract

Redox mediators are commonly used in microbial electrochemical systems to enable or enhance the electron transfer between microorganisms and electrodes. In recent studies, new insights into the mechanism of mediated extracellular electron transfer were gained, but some questions remain unanswered. In this review, some of the most outstanding research questions regarding the use of redox mediators in microbial electrochemical systems were discussed. These included the recycling of artificial and natural redox mediators, limitations in electron transfer rates by mediator turnover, metabolic burden, membrane permeability, and the putative interaction sites between commonly used redox mediators and the proteins of the electron transport chain of diverse electroactive microorganisms. To simplify the planning of mediator‐based bioelectrochemical systems, these molecular interaction sites were defined by their redox potential and are assigned to redox mediators, known or hypothesized to be able to transfer electrons from or to the specific interaction site. Furthermore, we addressed the kinetics of mediator transfer through the membrane and the potential rate‐limiting step in mediator‐based processes.

Renewable electron-driven bioinorganic nitrogen fixation: a superior route toward green ammonia?

“…51,52 The following criteria are typically taken into consideration for the determination of exogenous mediators: (i) widely accessible or simply producible via electrochemistry, (ii) electropositive enough to reduce NAD(P)H directly for effective energy transfer to cellular metabolism, and (iii) highly soluble in aquatic solution and non-highly toxic. 53…”

“…In addition, exogenous mediators for promoting indirect electron transfer in bioelectrocatalysis will also bring an underlying obstacle: downstream removing and recycling redox mediators from the fermentation broth. 53 Thus, whether importing an intelligent algorithm into bioelectrocatalysis can effectively regulate or circumvent the above challenges, more efforts are required.…”

“…51,52 The following criteria are typically taken into consideration for the determination of exogenous mediators: (i) widely accessible or simply producible via electrochemistry, (ii) electropositive enough to reduce NAD(P)H directly for effective energy transfer to cellular metabolism, and (iii) highly soluble in aquatic solution and non-highly toxic. 53 As increasingly sophisticated extracellular electron transfer mechanisms are investigated in the biotechnology application of electromicrobiology, 54,55 the e-BNF routes provide an alternative avenue to synthesize ammonia. Compared to other approaches, e-BNF empowers unique merits of potentially sustainable, widespread scopes of the feed substrates, ambient reaction conditions, high selectivity, and high energy efficiency.…”

Anodic Respiration of Vibrio natriegens in a Bioelectrochemical System

“…Some of those shuttles are capable of traversing the (outer) membrane which grants them access to periplasmic or cytoplasmic interaction sites [10] . The mediators can be distinguished into two main groups, artificial or self‐synthesized natural molecules [11] …”

“…[10] The mediators can be distinguished into two main groups, artificial or selfsynthesized natural molecules. [11] This study aimed to investigate the mediated and direct electron transfer of V. natriegens. Hence, special attention is devoted to characterizing growth and product formation under the artificial electrochemical cultivation conditions.…”