代谢工程改造大肠杆菌从头合成1,4-丁二醇

Metabolic engineering of Escherichia coli for de novo synthesis of 1,4-butanediol

1,4-丁二醇是一种重要的中间体,广泛应用于化工、农业、医药等领域。本研究将酶工程和代谢工程相结合,构建了一条以葡萄糖为底物生产1,4-丁二醇的新途径。首先,通过数据库挖掘设计了一条包含α-酮酸脱羧酶(α-ketoglutarate decarboxylase,SucA)、羧酸还原酶(carboxylate reductase,Car)、乙醇脱氢酶(alcohol dehydrogenase,YqhD)的新型催化途径,引入底盘细胞W3110(K-12)后,实现了1,4-丁二醇的从头合成。为进一步提高该路径的合成效率,敲除了乳酸脱氢酶(lactate dehydrogenase A,LdhA)、丙酮酸甲酸裂解酶(pyruvate formate lyase B,PflB)基因,阻断旁路代谢途径;强化表达柠檬酸合酶(citrate synthase,GltA^(R163L)),增加α-酮戊二酸代谢通量;强化底盘细胞中关键辅酶NADPH合成量并替换强启动子强化sucA、car、yqhD基因表达量,改善了1,4-丁二醇合成前体的供给效率。最终,重组菌株摇瓶发酵48 h最高合成770 mg/L的1,4-丁二醇,在5 L发酵罐上发酵60 h,1,4-丁二醇产量达4.22 g/L,得率为12.46 mg/g葡萄糖。本研究设计了一条新的1,4-丁二醇从头合成路径,与已报道的路径相比,该路径无需乙酰辅酶A参与,避免了副产物乙酸的积累,同时避免了氨的添加,为代谢工程改造生产1,4-丁二醇及其高附加值衍生产品提供了一种新的思路。

1,4-butanediol is an important intermediate widely used in chemical,agricultural,and pharmaceutical industries.This study constructed a new short path for the production of 1,4-butanediol with glucose as the substrate by combining enzyme engineering and metabolic engineering.Firstly,a novel path catalyzed byα-ketoglutarate decarboxylase(SucA),carboxylate reductase(Car),and alcohol dehydrogenase(YqhD)was designed by database mining,and the de novo synthesis of 1,4-butanediol was achieved after introduction of the path into Escherichia coli W3110(K-12)chassis cells.To further improve the synthesis efficiency of this path,we deleted the genes encoding lactate dehydrogenase A(LdhA)and pyruvate formate lyase B(PflB)to block the metabolic bypass.Furthermore,the expression of citrate synthase(GltA^(R163L))was up-regulated to increase theα-ketoglutarate metabolic flux.In addition,we improved the synthesis of the key cofactor NADPH and up-regulated the expression of sucA,car,and yqhD by substituting with strong promoters to increase the efficiency of supplying precursors to 1,4-butanediol synthesis.Eventually,the recombinant strain produced up to 770 mg/L of 1,4-butanediol within 48 h in a shake flask,and 4.22 g/L of 1,4-butanediol within 60 h in a 5 L fermenter with a yield of 12.46 mg/g glucose.Compared with the previously reported method,the novel path designed in this study for the de novo synthesis of 1,4-butanediol does not need acetyl coenzyme A and avoids the byproduct acetate or the addition of ammonia.Therefore,the outcome is expected to provide a new idea for the metabolic engineering of microbial chassis for the production of 1,4-butanediol and its high-value derivatives.