Department of Chemical and Biological Engineering, Korea University, Seoul, Korea.
School of Energy and Chemical Engineering, UNIST, Ulsan, Korea.
Biotechnol J. 2017 Nov;12(11). doi: 10.1002/biot.201700121. Epub 2017 Aug 14.
Anaerobic bioprocessing is preferred because of its economic advantages. However, low productivity and decreased growth of the host strain have limited the use of the anaerobic process. Anaerobic respiration can be applied to anoxic processing using formate and nitrate metabolism to improve the productivity of value-added metabolites. A isobutanol-producing strains is constructed using Enterobacter aerogenes as a host strain by metabolic engineering approaches. The byproduct pathway (ldhA, budA, and pflB) is knocked out, and heterologous keto-acid decarboxylase (kivD) and alcohol dehydrogenase (adhA) are expressed along with the L-valine synthesis pathway (ilvCD and budB). The pyruvate formate-lyase mutant shows decreased growth rates when cultivated in semi-anaerobic conditions, which results in a decline in productivity. When formate and nitrate are supplied in the culture medium, the growth rates and amount of isobutanol production is restored (4.4 g L , 0.23 g g glucose, 0.18 g L h ). To determine the function of the formate and nitrate coupling reaction system, the mutant strains that could not utilize formate or nitrate is contructed. Decreased growth and productivity are observed in the nitrate reductase (narG) mutant strain. This is the first report of engineering isobutanol-producing E. aerogenes to increase strain fitness via augmentation of formate and nitrate metabolism during anaerobic cultivation.
由于经济优势，厌氧生物处理受到青睐。然而，由于宿主菌株的低生产力和生长减少，限制了厌氧工艺的使用。可以应用厌氧呼吸来进行缺氧处理，利用甲酸盐和硝酸盐代谢来提高增值代谢物的生产力。通过代谢工程方法，使用肠杆菌 Aerogenes 作为宿主菌株来构建生产异丁醇的菌株。敲除副产物途径（ldhA、budA 和 pflB），并表达异源酮酸脱羧酶（kivD）和醇脱氢酶（adhA）以及 L-缬氨酸合成途径（ilvCD 和 budB）。在半厌氧条件下培养时，丙酮酸甲酸裂解酶突变体的生长速率降低，导致生产力下降。当培养基中供应甲酸盐和硝酸盐时，生长速率和异丁醇产量恢复（4.4 g/L、0.23 g/g 葡萄糖、0.18 g/L·h）。为了确定甲酸盐和硝酸盐偶联反应系统的功能，构建了不能利用甲酸盐或硝酸盐的突变菌株。硝酸盐还原酶（narG）突变株的生长和生产力下降。这是首次报道通过增强厌氧培养过程中甲酸盐和硝酸盐代谢来提高产异丁醇的肠杆菌 Aerogenes 菌株的适应性。
