Gas fermentation is a promising biological process for the conversion of CO₂ or syngas into valuable chemicals. Homoacetogens are microorganisms growing autotrophically using CO₂ and H₂ or CO and metabolizing them to form acetate coupled with energy conservation. The challenge in the metabolic engineering of the homoacetogens is divergence of the acetate formation, whose intermediate is acetyl-CoA, to a targeted chemical with sufficient production of adenosine triphosphate (ATP). In this study, we report that an engineered strain of the thermophilic homoacetogen Moorella thermoacetica, in which a pool of acetyl-CoA is diverted to ethanol without ATP production, can maintain autotrophic growth on syngas. We estimated the ATP production in the engineered strains under different gaseous compositions by considering redox-balanced metabolism for ethanol and acetate formation. The culture test showed that the combination of retaining a level of acetate production and supplying the energy-rich CO allowed maintenance of the autotrophic growth during ethanol production. In contrast, autotrophy was collapsed by complete elimination of the acetate pathway or supplementation of H₂–CO₂. We showed that the intracellular level of ATP was significantly lowered on H₂–CO₂ in consistent with the incompetence. In the meantime, the complete disruption of the acetate pathway resulted in the redox imbalance to produce ethanol from CO, albeit a small loss in the ATP production. Thus, preservation of a fraction of acetate formation is required to maintain sufficient ATP and balanced redox in CO-containing gases for ethanol production.

气体发酵是一种很有前途的将 CO ₂或合成气转化为有价值化学品的生物过程。Homoacetogens 是使用 CO ₂和 H ₂或 CO自养生长的微生物，并将它们代谢成乙酸盐，同时节约能源。同型产乙酸菌的代谢工程面临的挑战是将中间体为乙酰辅酶 A 的乙酸盐形成发散为具有足够三磷酸腺苷 (ATP) 产量的目标化学品。在这项研究中，我们报告了嗜热同型乙酸菌穆雷拉热乙酸菌的工程菌株，其中乙酰辅酶 A 池在不产生 ATP 的情况下被转移到乙醇中，可以保持合成气的自养生长。我们通过考虑乙醇和乙酸盐形成的氧化还原平衡代谢来估计不同气体成分下工程菌株的 ATP 产量。培养试验表明，保持一定水平的醋酸盐生产和提供富含能量的 CO 相结合，可以在乙醇生产过程中维持自养生长。相反，通过完全消除乙酸盐途径或补充 H ₂ -CO ₂，自养被破坏。我们发现细胞内 ATP 水平在 H ₂ –CO ₂上显着降低与无能相一致。与此同时，醋酸盐途径的完全中断导致氧化还原失衡，以从 CO 生产乙醇，尽管 ATP 生产有少量损失。因此，需要保留一部分乙酸盐形成以在乙醇生产中维持含 CO 气体中足够的 ATP 和平衡的氧化还原。