Enhanced production of d-psicose 3-epimerase in Bacillus subtilis by regulation of segmented fermentation.

d-Psicose 3-epimerase is an enzyme that catalyzes the synthesis of d-psicose from d-fructose. We cloned the d-psicose 3-epimerase from Ruminococcus sp. (RDPE) and expressed it in Bacillus subtilis A311. By a two-step pH regulation of segmented fermentation, we significantly improved the RDPE production and decreased the fermentation cost. The two-step regulation consisted of the first step maintained the pH value at 7.0 for 24 H and the second step adjusted the pH value up to 7.5 slowly for another 24 H. Finally, the RDPE production was increased to 74 U/mL, which was about 2.5-fold compared with the control. Our segmented fermentation strategy provides an important experimental basis for the industrial-scale production of RDPE.