Development of a recombinant D-mannose isomerase and its characterizations for D-mannose synthesis

D-Mannose isomerase (MIase) catalyzes the conversion of D-fructose to D-mannose. In this study, the MIase encoding gene (yihS) from Escherichia call BL21 contains an ORF of 1242 bp, was cloned and expressed in Bacillus subtilis WB800. This heterologous expression resulted in a hexamer with a molecular weight of 274.5 kDa and T-m of 61.4 degrees C. Efficient Mlase secretory expression by the robust recombinant B. subtilis was achieved with activity of 51.2 U/ml (D-mannose forming). Its optimal temperature and pH were 45.0 degrees C and 7.0, respectively. Using D-fructose as the substrate, K-m, k(cat) and catalytic efficiency value of kinetic reaction were 203.7 +/- 6.7 mM, 27.7 +/- 0.7 s(-1) and 136.0 +/- 2.9 M-1 s-1, respectively. The production of D-mannose reached about 150 g/l with approximately 25% turnover yield under the optimum conditions. These results demonstrated that B. subtilis was a promising candidate of Mlase expression system for D-mannose production. (C) 2016 Elsevier B.V. All rights reserved.