CO–Driven Bioconversion of Carbon Substrates into C ₂ –C ₄ Carboxylates by Mixed Microbial Communities for Sustainable Carbon Valorization

As an intermediate in the CO2 reduction reaction, CO is recognized as a highly effective carbon and energy substrate for certain bacteria. Our study demonstrates that high CO concentrations (85–94%) enhance the bioconversion of carbon into short-chain carboxylates in mixed microbial communities, leading to increased acetate, propionate, and butyrate production, with C3–C4 carboxylate synthesis dependent on acetate accumulation. Microbial analysis identified Acetobacterium as the dominant genus (49.9 ± 0.7%), while CO enrichment significantly increased the abundances of Clostridium, Oscillibacter, Soehngenia, and Acetoanaerobium (p < 0.05). Metagenomic and metatranscriptomic analyses revealed the upregulation of genes associated with acetate, propionate, and butyrate biosynthesis under high CO conditions. We propose a metabolic model where ethanol and acetate produced by acetogen Bin44 (Acetobacterium wieringae) are utilized by propionate-producing Bin130 (Oscillibacter sp.) via the acrylate pathway and by butyrate-producing Bin55 (Clostridium sp.) through the reverse β-oxidation pathway. This study advances our understanding of CO-driven microbial C2–C4 carboxylates production, providing a theoretical foundation for optimizing microbial communities to improve carbon utilization efficiency and facilitate the practical implementation of carbon valorization strategies.