[Efficient biosynthesis of <subscript>D</subscript> -mannitol by coordinated expression of a two-enzyme cascade].

D -mannitol is widely used in the pharmaceutical and medical industries as an important precursor of antitumor drugs and immune stimulants. However, the cost of the current enzymatic process for D -mannitol synthesis is high, thus not suitable for commercialization. To address this issue, an efficient mannitol dehydrogenase Lp GDH used for the conversion and a glucose dehydrogenase Ba GDH used for NADH regeneration were screened, respectively. These two enzymes were co-expressed in Escherichia coli BL21(DE3) to construct a two-enzyme cascade catalytic reaction for the efficient synthesis of d-mannitol, with a conversion rate of 59.7% from D -fructose achieved. The regeneration of cofactor NADH was enhanced by increasing the copy number of Bagdh , and a recombinant strain E . coli BL21/pETDuet- Lpmdh - Bagdh - Bagdh was constructed to address the imbalance between cofactor amount and key enzyme expression level in the two-enzyme cascade catalytic reaction. An optimized whole cell transformation process was conducted under 30 ℃, initial pH 6.5, cell mass ( OD 600 ) 30, 100 g/L D -fructose substrate and an equivalent molar concentration of glucose. The highest yield of D -mannitol was 81.9 g/L with a molar conversion rate of 81.9% in 5 L fermenter under the optimal conversion conditions. This study provides a green and efficient biotransformation method for future large-scale production of D -mannitol, which is also of great importance for the production of other sugar alcohols.