Production of D-psicose from D-glucose by co-expression of D-psicose 3-epimerase and xylose isomerase

n-Psicose has been drawing increasing attention in recent years because of its medical and health applications. The production of D-psicose from n-glucose requires the co-expression and synergistic action of xylose isomerase and n-psicose 3-epimerase. To co-express these genes, vector pET-28a(+)-dual containing two T7 promoters and RBS sites and an Multiple Cloning Sites was constructed using the Escherichia colt expression plasmid pET-28a). The xylose isomerase gene from E. coli MG1665 and the 0-psicose 3-epimerase gene from Agrobacterium tumefaciens CGMCC 1.1488 were cloned and co-expressed in E. coli BL21(DE3). After 24 h incubation with the dual enzyme system at 40 degrees C, the sugar conversion ratio from n-glucose to D-psicose reached 10%. The optimal conditions were 50 degrees C, pH 7.5 with Co2+ and Mg2+. The D-psicose yields from sugarcane bagasse and microalgae hydrolysate were 1.42 and 1.69 g/L, respectively.