Gas fermentation processes have attracted considerable attention in recent years as they hold high potential for capturing and converting C1 waste gases into a range of biofuels and commodity chemicals. The production of solvents in gas fermentation is typically achieved by exploiting the solventogenic metabolism of acetogenic cultures, which is generally triggered upon exposure to stressful conditions, e.g. low pH. Although the oxidoreduction potential (ORP) is a well-known trigger of the cellular stress response, it has been scarcely investigated as a process control parameter in gas fermentation. Thus, this study focused on evaluating the potential of ORP control strategies for boosting the productivity of ethanol by exploiting the metabolic response to oxidative stress of acetogenic cultures. The dynamics of the redox cofactor pool and ratio as a function of the extracellular ORP and other operational parameters were also studied by monitoring the intracellular levels of the redox cofactor NADH/NAD⁺. The results showed that increasing the ORP to oxidizing conditions using dilute H₂O₂ triggered a 3.7-fold increase in the specific ethanol productivity, from 0.63 ± 0.04 mmol∙gCDW⁻¹ h⁻¹ at an ORP of -210 mV to 2.32 ± 0.19 mmol∙gCDW⁻¹ h⁻¹ at 160 mV. Additionally, the concentration and product selectivity towards ethanol also increased considerably due to the partial inhibition of the chain elongation under oxidative stress. Boost in ethanol productivity and inhibition of the chain elongation were both found to be driven by the presence of H₂O₂ rather than by the ORP per se. Studying the profile of the redox cofactors revealed a highly dynamic nature in the pool and ratio of NADH/NAD⁺ as a function of the specific uptake rate and the ratio of acetate-to-ethanol, respectively. The latter was explained by analyzing the thermodynamics of the aldehyde:ferredoxin oxidoreductase (AOR) pathway, which showed that the intrinsic thermodynamic limitation of this pathway imposes a high Fd_red/Fd_ox ratio (>88 % of reduced ferredoxin) while forcing a highly dynamic NADH/NAD⁺ ratio in order to maintain the thermodynamic drive in the forward direction. The dynamics of the NADH/NAD⁺ ratio were also found to be significantly affected by the oxidative stress triggered by dilute H₂O₂, which confirmed the involvement of the AOR pathway in the detoxification of reactive oxygen species.

近年来，气体发酵过程引起了相当多的关注，因为它们在捕获 C1 废气并将其转化为一系列生物燃料和商品化学品方面具有很高的潜力。气体发酵中溶剂的生产通常是通过利用产乙酸培养物的产溶剂代谢来实现的，这通常在暴露于压力条件（例如低 pH）时触发。尽管氧化还原电位 (ORP) 是众所周知的细胞应激反应触发因素，但很少有人将其作为气体发酵过程控制参数进行研究。因此，本研究的重点是评估 ORP 控制策略通过利用产乙酸培养物对氧化应激的代谢反应来提高乙醇生产力的潜力。⁺。结果表明，使用稀释的 H ₂ O ₂将 ORP 增加到氧化条件引发了比乙醇生产率增加 3.7 倍，从ORP 为 -210 mV 时的0.63 ± 0.04 mmol∙gCDW ^-1 h ^-1增加到 2.32 ± 0.19 mmol∙gCDW ^-1 h ^-1在 160 mV。此外，由于氧化应激下链延长的部分抑制，对乙醇的浓度和产物选择性也显着增加。发现乙醇生产率的提高和链延长的抑制都是由 H ₂ O ₂的存在而不是由 ORP本身驱动的. 研究氧化还原辅因子的分布揭示了池中的高度动态特性，以及 NADH/NAD ^{+ 的}比率分别作为特定摄取率和乙酸盐与乙醇比率的函数。后者是通过分析醛：铁氧还蛋白氧化还原酶 (AOR) 途径的热力学来解释的，这表明该途径的内在热力学限制强加了高 Fd _red / Fd _ox比率（> 88 % 的还原铁氧还蛋白），同时迫使高度动态 NADH/NAD ⁺比率，以保持正向热力学驱动。还发现NADH/NAD ⁺比率的动态受到稀释 H ₂引发的氧化应激的显着影响O ₂，这证实了 AOR 途径参与活性氧的解毒。