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

Abstract:

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 by α-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 the α-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.