Artificial Soil-Like Material Enhances CO₂ Bio-Valorization into Chemicals in Gas Fermentation

Gas fermentation offers a carbon-neutral route for producing industrial feedstocks using autotrophic microbes to convert carbon dioxide (CO 2 ) in waste gases, such as industrial emissions and biogas, into valuable chemicals or biofuels. However, slow microbial metabolism owing to low gaseous solubility causes significant challenges in gas fermentation. Although chemical or genetic manipulations have been explored to improve gas fermentation, they are either nonsustainable or complex. Herein, an artificial soil-like material (SLM) inspired by natural soil was fabricated to improve the growth and metabolism of Cupriavidus necator for enhanced poly-β-hydroxybutyrate (PHB) biosynthesis from CO 2 and hydrogen (H 2 ). Porous SLM comprises low-cost nanoclay, boehmite, and starch and serves as a biocarrier to facilitate the colonization of bacteria and delivery of CO 2 to bacteria. With 3.0 g/L SLM addition, the solubility of CO 2 in water increased by ∼4 times and biomass and PHB production boosted by 29 and 102%, respectively, in the 24 h culture. In addition, a positive modulation was observed in the metabolism of PHB biosynthesis. PHB biosynthesis-associated gene expression was found to be enhanced in response to the SLM addition. The concentrations of intermediates in the metabolic pathway of PHB biosynthesis, such as pyruvate and acetyl-CoA, as well as reducing energy (ATP and NADPH) significantly increased with SLM addition. SLM also demonstrated the merits of easy fabrication, high stability, recyclability, and plasticity, thereby indicating its considerable potential for large-scale application in gas fermentation.