Sodium limitation stimulates Acetobacterium woodii enrichment and boosts CO2 conversion to acetate in self-controlled microbial electrosynthesis systems

Microbial electrosynthesis system (MES) enables the conversion of CO₂ into acetate with low energy consumption. However, the accumulation of acetate brings inevitable survival troubles to the model microorganisms, the coulombic efficiency of MES is far from the theoretical value. Establishing a self-controlled system and providing optimized living conditions for model microorganisms can be regarded as a strategy to improve the coulombic efficiency. In this study, a flux-pH adaptive MES coupled with Acetobacterium woodii was constructed and the Na ⁺ -dependent characteristics of A. Woodii was first found. Na ⁺ -free stimulated the metabolic pathway of A. woodii and thus enhanced coulombic efficiency, acetate accumulation, and production rate in MES with the value of 62 %, 16.7 g/L, and 0.92 g/(L·d), respectively. These values represented increases of 61 %, 97 %, and 61 % compared to the control group. The abundance of A. woodii in Na ⁺ -free group was maintained between 28 % and 44 %. After medium renewal in Cycle 2, acetate accumulation further increased to 17.4 g/L, driven by the sustained dominance of A. Woodii, which was the highest yield rate reported so far. Moreover, the purity of the isolated sodium acetate produced in the MES reached 91 % after 70-day operation period. These results indicated that controlling the concentration of Na ⁺ can provide survival competitiveness for A. Woodii, while the continuous acetate production needs intelligent control system to cooperate. This provides a new perspective for the application of MES.