Enhanced Succinate Production in Actinobacillus succinogenes via Neutral Red Bypass Reduction in a Novel Bioelectrochemical System

Carbon capture and power-to-X are becoming increasingly relevant in the context of decarbonization and supply security. <i>Actinobacillus succinogenes</i> is capable of transforming CO₂ into succinate, whereby product formation is significantly limited by the availability of NADH. The aim of this work was to further develop a bioelectrochemical system (BES) in order to provide additional reduction equivalents and thus increase yield and titer. To this end, a new BES configuration was established. A conventional stirred tank reactor (STR) is coupled via a bypass to an H-cell, in which the redox mediator neutral red (NR) is electrochemically reduced and then returned back to the bioreactor. The indirect electron transfer decouples the electrochemical reduction from the biology and results in increased intracellular availability of NADH. The present approach resulted in an increase in yield from 0.64 g·g^-1 to 0.76 g·g^-1, corresponding to an increase of 18%. At the same time, a titer of 16.48 ± 0.19 g·L^-1 was achieved in the BES, compared to 12.05 ± 0.18 g·L^-1 in the control. The results show that the mediator-assisted, partially decoupled BES architecture significantly improves CO₂-based succinate production and opens up a scalable path to the use of renewable electricity as a reduction source in power-to-X processes.