Metabolic engineering of Escherichia coli for improved D-pantothenic acid biosynthesis by enhancing NADPH availability

Microbial production of D-pantothenic acid from renewable carbon sources has attracted significant attention in recent years. Cofactor NADPH is involved in a variety of synthetic metabolic reactions, and its availability is considered to play a key role in biotransformation. In this study, nicotinamide and niacin, the precursors of NADPH, were supplemented to the growth medium of a wild-type Escherichia coli strain DPA11A01. Results showed that the addition of nicotinamide and niacin to the medium led to a significant increase in the levels of Dpantothenic acid, which were 22.76 % and 29.84 % higher than those of without precursor, respectively. Furthermore, the essential genes (zwf, icd, maeB, pntAB, sthA, yfjB, ppnk or pos5) for NADPH de novo synthesis were selected and co-overexpressed to increase the intracellular NADPH pool. The recombinant strain DPA11A14 carrying pos5 and ppnk co-expression plasmid reached 2.45 p.mol NADPH /g DCW, while the control strain yielded 0.38 p.mol NADPH /g DCW. Increased NADPH supply in the cells significantly enhanced D-pantothenic acid accumulation. The D-pantothenic acid titer of the co-overexpression strain DPA11A14 could reach 6.32 g/L in shake flask cultivation, which increased 53.4 % than that of the control. Fed-batch fermentation in 5-L bioreactor employing strain DPA11A14 allowed production of 63.58 g/L D-pantothenic acid with productivity of 0.73 g/L/h and yield of 0.33 g/g glucose. This study provides a productive D-pantothenic acid fermentation strain and an effective cofactor manipulating strategy for enhancing of NADPH-dependent products.