利用代谢工程构建D-甘露醇生产菌株

D-甘露醇广泛应用于食品、制药、化学品工业等领域。从野生型大肠杆菌出发，将来自假肠膜明串珠菌Leuconostoc pseudomesenteroides ATCC 12291菌株的甘露醇脱氢酶与果糖转运蛋白编码基因整合到大肠杆菌ATCC 8739的染色体中，并失活其他的发酵途径 (丙酮酸甲酸裂解酶、乳酸脱氢酶、富马酸还原酶、乙醇脱氢酶、甲基乙二醛合成酶和丙酮酸氧化酶) ，构建了一株遗传稳定的D-甘露醇生产菌株。使用无机盐培养基和葡萄糖果糖作为混合碳源，厌氧发酵6 d，D-甘露醇产量达1.2 mmol/L。基于细胞生长和D-甘露醇合成的偶联，进一步通过代谢进化技术提高细胞合成D-甘露醇的生产能力。经过80代的驯化，D-甘露醇产量提高了2.6倍，甘露醇脱氢酶的活性提高了2.8倍。构建获得的遗传稳定的工程菌能直接发酵糖生产D-甘露醇，不需添加抗生素、诱导剂和甲酸，在工业化生产时有一定优势。

Production of D-mannitol by metabolically engineered Escherichia coli

D-Mannitol has wide applications in food, pharmaceutical, and chemical industries. In this study, we constructed a genetically stable Escherichia coli strain for D-mannitol production by integrating mannitol dehydrogenase (mdh) and fructose permease (fupL) genes of Leuconostoc pseudomesenteroides ATCC 12291 into chromosome of E. coli ATCC 8739 and inactivating other fermentation pathways (including pyruvate formate-lyase, lactate dehydrogenase, fumarate reductase, alcohol dehydrogenase, methylglyoxal synthase and pyruvate oxidase). Using mineral salts medium with glucose and fructose as carbon sources, the engineered strain could produce 1.2 mmol/L D-mannitol after anaerobic fermentation for 6 days. Based on the coupling of cell growth and D-mannitol production, metabolic evolution was used to improve D-mannitol production. After evolution for 80 generations, D-mannitol titer increased 2.6-fold and mannitol dehydrogenase activity increased 2.8-fold. Genetically stable strains constructed in this work could ferment sugars to produce D-mannitol without the addition of antibiotics, inducers and formate, which was favorable for industrial production.