Exploring Mediated Electron Transfer in Vibrio natriegens

Vibrio natriegens is a promising biotechnological chassis distinguished by exceptionally rapid growth and dynamic metabolism. This microorganism can deliver electrons both directly to electrodes via the well-established MtrCAB electron export system, as well as mediated through redox shuttle molecules. Notably, mediated electron transfer (MET) results in higher currents. Bioelectrochemical systems offer a possibility to influence the metabolic product spectrum of V. natriegens by using a poised anode as terminal electron acceptor. This study systematically evaluated twelve mediators spanning a redox potential window from −520 to +490 mV versus Ag/AgCl (3 M KCl) to establish efficient MET in V. natriegens. Among the tested compounds, potassium ferricyanide yielded the highest current densities (104 ± 20 µA cm−2) and faradaic efficiency. Interestingly, riboflavin underwent less than 0.05 cycles of shuttling, indicating a low electron shuttling capability. In contrast, phenazines demonstrated efficiency for electron uptake from V. natriegens cells, but the current production was unstable. Overall, a specific redox potential window above −220 mV versus Ag/AgCl was identified within which mediator reduction occurred most efficiently. These findings establish a catalog of compatible redox shuttles and lay the basis for increased efficiency of bioelectrochemical processes leveraging V. natriegens.