초록
<P><B>Background</B></P><P><SMALL>D</SMALL>-Psicose 3-epimerase (DPEase) catalyzes the isomerization of <SMALL>D</SMALL>-fructose to the rare sugar <SMALL>D</SMALL>-psicose, which may help prevent obesity, reduce blood sugar and blood fat, and inhibit intra-abdominal fat accumulation.</P><P><B>Results</B></P><P>In this study, the DPEase of <I>Clostridium cellulolyticum</I> H10 was expressed in the food-grade host <I>Bacillus subtilis</I>. Optimization of the culture medium during shake-flask experiments yielded a DPEase activity of 314 U/mL. The optimal medium included 20 g/L peptone, 15 g/L corn steep powder, 5 g/L glycerol, and 1 mM Ca<SUP>2+</SUP>. Controlling the carbon source concentration was important because elevated concentrations can result in catabolite metabolic suppression (CCR). To avoid CCR and increase DPEase expression, we developed a fed-batch strategy in a 3.6-L fermenter. We altered the ratio of carbon source to nitrogen source (C/N) in the feeding medium and employed a constant feeding rate (6 g/L/h). This strategy improved the DPEase activity to 2246 U/mL (7.8 g/L), which is almost 15 times higher than that observed in the original shake-flask cultures. Finally, we used the DPEase-expressing <I>B. subtilis</I> cells to produce <SMALL>D</SMALL>-psicose from <SMALL>D</SMALL>-fructose, and a 28% conversion yield was achieved with these cells, demonstrating their potential use in <SMALL>D</SMALL>-psicose production.</P><P><B>Conclusions</B></P><P>This is the first report to enhance recombinant DPEase production in <I>B. subtilis</I> using efficient and convenient fermentation strategy, and the DPEase yield is three times higher than the highest yield reported to date. The recombinant <I>B. subtilis</I> cells were further used in the efficient synthesis of <SMALL>D</SMALL>-psicose. This study provides a basis for the industrial production of <SMALL>D</SMALL>-psicose.</P>