Single-Stage Coculture System Using <i>Clostridium kluyveri</i> and Acetogens Outperforms a Two-Stage Monoculture System for Syngas Bioconversion to Medium Chain Fatty Acids

This study examined an integrated bioprocess involving the coculture of acetogens and a chain-elongating bacterium in single-stage and two-stage systems for producing medium-chain fatty acids from syngas. The impact of three acetogens, Clostridium carboxidivorans, Clostridium ragsdalei, and Clostridium ljungdahlii, on the chain elongation efficiency by C. kluyveri using the in situ produced acetate and ethanol from syngas fermentation was evaluated in batch experiments. Among the studied combinations, C. carboxidivorans with C. kluyveri coculture showed the highest production of hexanoate (9.54 mM) and butyrate (3.70 mM), whereas coculture using either C. ragsdalei, or C. ljungdahlii with C. kluyveri produced hexanoate of 8.42 and 6.52 mM, respectively. The findings highlight that acetogen selection significantly influences the product distribution and yield. Furthermore, single-stage cocultures outperformed two-stage systems by promoting efficient metabolite cross-feeding, reducing process time, and enhancing overall yield of C4–C8 compounds through synergistic interactions in syngas bioconversion.