Microbial fermentation of synthesis gas (syngas) is becoming more attractive for sustainable production of commodity chemicals. To date, syngas fermentation focuses mainly on the use of Clostridium species for the production of small organic molecules such as ethanol and acetate. The co-cultivation of syngas-fermenting microorganisms with chain-elongating bacteria can expand the range of possible products, allowing, for instance, the production of medium-chain fatty acids (MCFA) and alcohols from syngas. To explore these possibilities, we report herein a genome-scale, constraint-based metabolic model to describe growth of a co-culture of Clostridium autoethanogenum and Clostridium kluyveri on syngas for the production of valuable compounds. Community flux balance analysis was used to gain insight into the metabolism of the two strains and their interactions, and to reveal potential strategies enabling production of butyrate and hexanoate. The model suggests that one strategy to optimize the production of medium-chain fatty-acids from syngas would be the addition of succinate. According to the prediction, addition of succinate would increase the pool of crotonyl-CoA and the ethanol/acetate uptake ratio in C. kluyveri, resulting in a flux of up to 60$\%$ of electrons into hexanoate. Another potential way to further optimize butyrate and hexanoate production would be an increase of C. autoethanogenum ethanol production. Blocking either acetaldehyde dehydrogenase or formate dehydrogenase (ferredoxin) activity or formate transport, in the C. autoethanogenum metabolic model could potentially lead to an up to 150$\%$ increase in ethanol production.

合成气（syngas）的微生物发酵对于可持续生产商品化学品变得越来越有吸引力。迄今为止，合成气发酵主要集中在梭状芽胞杆菌物种的生产中，用于生产小的有机分子，例如乙醇和乙酸盐。合成气发酵微生物与链延长细菌的共培养可以扩大可能产物的范围，例如，允许从合成气生产中链脂肪酸（MCFA）和醇。为了探索这些可能性，我们在此报告了一种基于基因组规模，基于约束的代谢模型来描述梭菌梭状芽胞杆菌和克鲁维氏梭菌的共培养物的生长。合成气生产有价值的化合物。社区通量平衡分析用于深入了解这两种菌株的代谢及其相互作用，并揭示实现丁酸和己酸生产的潜在策略。该模型表明，优化合成气中链脂肪酸生产的一种策略是添加琥珀酸酯。根据预测，琥珀酸的添加将增加克鲁维酵母中巴豆酰-CoA的库和乙醇/乙酸盐的吸收比，从而导致通量高达60$％$电子变成己酸。进一步优化丁酸和己酸产量的另一种潜在方法是增加自产乙醇梭菌乙醇的产量。阻断乙醛脱氢酶或甲酸盐脱氢酶（铁氧还蛋白）的活性或甲酸盐的运输，在C.autoethanogenum代谢模型中可能导致多达150$％$ 增加乙醇产量。