Enhanced direct gaseous CO₂ fixation into higher bio-succinic acid production and selectivity

Utilizing CO₂ for bio-succinic acid production is an attractive approach to achieve carbon capture and recycling (CCR) with simultaneous production of a useful platform chemical. Actinobacillus succinogenes and Basfia succiniciproducens were selected and investigated as microbial catalysts. Firstly, the type and concentration of inorganic carbon concentration and glucose concentration were evaluated. 6 g C/L MgCO₃ and 24 g C/L glucose were found to be the optimal basic operational conditions, with succinic acid production and carbon yield of over 30 g/L and over 40%, respectively. Then, for maximum gaseous CO₂ fixation, carbonate was replaced with CO₂ at different ratios. The "less carbonate more CO₂" condition of the inorganic carbon source was set as carbonate: CO₂ = 1:9 (based on the mass of carbon). This condition presented the highest availability of CO₂ by well-balanced chemical reaction equilibrium and phase equilibrium, showing the best performance with regarding CO₂ fixation (about 15 mg C/(L·hr)), with suppressed lactic acid accumulation. According to key enzymes analysis, the ratio of phosphoenolpyruvate carboxykinase to lactic dehydrogenase was enhanced at high ratios of gaseous CO₂, which could promote glucose conversion through the succinic acid path. To further increase gaseous CO₂ fixation and succinic acid production and selectivity, stepwise CO₂ addition was evaluated. 50%-65% increase in inorganic carbon utilization was obtained coupled with 20%-30% increase in succinic acid selectivity. This was due to the promotion of the succinic acid branch of the glucose metabolism, while suppressing the pyruvate branch, along with the inhibition on the conversion from glucose to lactic acid.