Intracellular CO₂ Capture Triggered Outperforming Biocatalytic Production of Selective Acetic Acid and Biohydrogen...

The increasing concentration of atmospheric carbon dioxide (CO₂) necessitates innovative biocatalytic strategies for its utilization in sustainable chemical production. This study introduces a novel electrofermentation (EF) platform integrating polycarbazole-based porous organic polymer (VJ-POP)-coated electrodes to enhance selective acetic acid (AA) biosynthesis by Bacillus subtilis. Impressive high surface area and tailored porosity facilitate efficient CO₂ capture, modulate intracellular metabolic fluxes, and improve electron transfer, thereby driving product specificity. In the bioreactor equipped with VJ-POP, AA production reached 2.11 g L^-1 with a yield of 0.48 g g^-1, achieving 71% of the theoretical maximum without genetic modifications. The process also resulted in enriched biohydrogen content (52%) in the biogas (H₂ + CO₂) composition, highlighting the synergistic effect of VJ-POP on CO₂ sequestration and microbial metabolism. Gene expression analysis revealed significant upregulation of ackA (acetate kinase) and pdhA (pyruvate dehydrogenase), while buk (butyrate kinase) was downregulated, ensuring metabolic selectivity toward AA. Cyclic voltammetry and impedance analysis unambiguously confirmed an interesting phenomenon of enhanced electron transfer and reduced charge-transfer resistance in VJ-POP-assisted systems. Computational analysis using density functional theory (DFT) revealed stronger binding energy for CO₂ (-17.4 kJ mol^-1) compared to H₂ (-2.5 kJ mol^-1), driven by a mix of van der Waals and weak electrostatic interactions for CO₂ versus solely weak van der Waals-based physisorption for H₂. This pioneering approach with unique investigation results presents a scalable and sustainable biocatalytic framework for CO₂ valorization, bridging material science and microbial electrochemical systems for selective AA and enhanced biohydrogen production.