The choice of redox mediator is a critical design factor in microbial bioelectrochemical systems. However, selecting between externally added (exogenous) or metabolically synthesized (endogenous) mediators remains challenging, and a direct in vivo comparison is missing. In this work, we selected ferricyanide and phenazine‐1‐carboxylic acid (PCA) as representatives of exogenous and endogenous mediators, and assessed their electrochemical performance and physiological effects in Pseudomonas putida KT2440 in a bio‐electrochemical system (BES). Under comparable conditions, ferricyanide enabled about 6‐times higher electron transfer rates, while, in contrast, PCA generated lower but long‐term stable current output signals. PCA biosynthesis imposed no detectable metabolic burden for the microbial cells and supported cellular adaptation to oxygen‐limited growth conditions. These results indicate that exogenous mediators are advantageous for applications that require faster electron transfer and metabolic flux, such as electro‐fermentation for biosynthesis, whereas endogenous mediators may be better suited for modulating intracellular metabolism and enabling stable electrochemical signaling, for example, in biosensing. Despite the mediator effects may change with the environmental condition or working hosts, our results provide the first direct comparison of endogenous and exogenous mediators under comparable BES conditions, and establish a framework for mediator selection based on electron‐transfer kinetics, metabolic coupling, and operational redox conditions.
Pause et al. (Thu,) studied this question.