Cornell University, Department of Biological and Environmental Engineering, Riley Robb Hall, Ithaca, New York 14853, USA.
Biotechnol Bioeng. 2012 Apr;109(4):913-21. doi: 10.1002/bit.24380. Epub 2011 Dec 7.
n-Butanol was produced continuously in a two-stage fermentor system with integrated product removal from a co-feed of n-butyric acid and glucose. Glucose was always required as a source of ATP and electrons for the conversion of n-butyrate to n-butanol and for biomass growth; for the latter it also served as a carbon source. The first stage generated metabolically active planktonic cells of Clostridium saccharoperbutylacetonicum strain N1-4 that were continuously fed into the second (production) stage; the volumetric ratio of the two fermentors was 1:10. n-Butanol was removed continuously from the second stage via gas stripping. Implementing a two-stage process was observed to dramatically dampen metabolic oscillations (i.e., periodical changes of solventogenic activity). Culture degeneration (i.e., an irreversible loss of solventogenic activity) was avoided by periodical heat shocking and re-inoculating stage 1 and by maintaining the concentration of undissociated n-butyric acid in stage 2 at 3.4 mM with a pH-auxostat. The system was successfully operated for 42 days during which 93% of the fed n-butyrate was converted to n-butanol at a production rate of 0.39 g/(L × h). The molar yields Y(n-butanol/n-butyrate) and Y(n-butanol/glucose) were 2.0, and 0.718, respectively. For the same run, the molar ratio of n-butyrate to glucose consumed was 0.358. The molar yield of carbon in n-butanol produced from carbon in n-butyrate and glucose consumed (Y(n-butanol/carbon) ) was 0.386. These data illustrate that conversion of n-butyrate into n-butanol by solventogenic Clostridium species is feasible and that this can be performed in a continuous system operating for longer than a month. However, our data also demonstrate that a relatively large amount of glucose is required to supply electrons and ATP for this conversion and for cell growth in a continuous culture.
在一个两级发酵罐系统中，连续生产正丁醇，同时从丁酸和葡萄糖的共进料中去除产物。葡萄糖始终是将丁酸转化为正丁醇和生物量生长所需的 ATP 和电子的来源；对于后者，它也作为碳源。第一阶段生成代谢活跃的丙酮丁醇梭菌 N1-4 浮游细胞，这些细胞连续进料到第二（生产）阶段；两个发酵罐的体积比为 1:10。正丁醇通过气体汽提从第二阶段连续去除。实施两级工艺被观察到显著抑制代谢振荡（即溶剂形成活性的周期性变化）。通过定期热冲击和重新接种第一级以及通过 pH-auxostat 将第二级未离解丁酸的浓度维持在 3.4mM，避免了培养物退化（即溶剂形成活性的不可逆丧失）。该系统成功运行了 42 天，在此期间，93%的进料丁酸转化为正丁醇，生产速率为 0.39g/（L×h）。摩尔产率 Y(n-丁醇/n-丁酸)和 Y(n-丁醇/葡萄糖)分别为 2.0 和 0.718。对于相同的运行，丁酸与葡萄糖消耗的摩尔比为 0.358。从丁酸和葡萄糖消耗的碳中生产的正丁醇的碳摩尔产率（Y(n-丁醇/碳)）为 0.386。这些数据表明，溶剂形成梭菌属将丁酸转化为正丁醇是可行的，并且可以在连续系统中运行一个多月。然而，我们的数据还表明，需要相对大量的葡萄糖来为这种转化和连续培养中的细胞生长提供电子和 ATP。
