Increasing the succinate yield in <i>Actinobacillus succinogenes</i> by fumigation of <scp> H ₂ </scp> in a bioreactor

Abstract The microbial conversion of CO 2 into value‐added chemicals offers a promising and scalable route for sustainable bioproduction, particularly under mild reaction conditions and with technically straightforward reactor configurations. Actinobacillus succinogenes , a natural succinate producer, can fix CO 2 through anaplerotic carboxylation but its product yield is limited by the metabolic availability of reducing equivalents. In this study, we demonstrate that the simultaneous fumigation with molecular hydrogen (H 2 ) and carbon dioxide (CO 2 ) enhanced succinate production in A. succinogenes . Hydrogen supplementation during fermentation yielded 0.79 ± 0.07 g g −1 glucose, representing a substantial increase compared with control fermentations and ranking among one of the highest yields reported in the literature for A. succinogenes 130Z under conditions that were not genetically modified. After 48 h, the succinate titer showed an increase of 29%, correlating directly with the net CO 2 fixation rate. Gas supplementation also influenced product selectivity, with succinate comprising 72% of total fermentation products under H 2 and CO 2 fumigation, compared with 62% under CO 2 alone. These findings demonstrate that H 2 functions as an effective external reducing agent, shifting the redox balance and promoting enhanced C 4 ‐dicarboxylate synthesis. This study advances the integration of CO 2 utilization and biological hydrogen valorization, offering a novel strategy for coupling microbial fermentation with carbon capture.