High production of d-psicose from d-fructose by immobilized whole recombinant Bacillus subtilis cells expressing d-psicose 3-epimerase from Agrobacterium tumefaciens.

Abstract

d-Psicose 3-epimerase (DPEase) can catalyze the isomerization of d-fructose to be rare sugar d-psicose, which has wide application prospects in the food and medical fields. In this study, the DPEase gene from Agrobacterium tumefaciens was constructed into plasmid pMA5, and was successfully expressed in the host Bacillus subtilis WB600 (B. subtilis). After optimization of the fermentation conditions, whole recombinant B. subtilis WB600/pMA5-At-DEPase(O) cells produced d-psicose from d-fructose with a conversion rate of 29.01±0.19%, which could be used for the efficient synthesis of d-psicose. To further improve the whole recombinant B. subtilis application, B. subtilis cells were immobilized onto a gel bead biocatalyst by Ca-alginate. After optimization of the biotransformation conditions, the conversion rate of the immobilized biocatalyst reached 20.74±0.39%, which was lower than the free cells. However, the results showed that the immobilized biocatalyst had higher thermal/pH stability and storability, and the gel beads could be recycled for at least six batches. The results showed that the amount of d-psicose generated reached 32.83±2.56g/L with the immobilized biocatalyst after six times biotransformation, whereas the free cells produced only approximately 10.44±0.07g/L. The results showed that immobilized recombinant B. subtilis cells are promising to use for the efficient synthesis of d-psicose.