Characterization of two novel D-mannose 2-epimerases from Dyadobacter sp. CY327 and Rhabdobacter roseus DSM 105074 and their application in D-mannose production

D-Mannose possesses many health effects and is commercially used in pharmaceutical, nutraceutical, and food industries. D-Mannose 2-epimerase (MEase) is responsible for bioconversion between D-glucose and D-mannose. In this study, two novel MEases were identified from Dyadobacter sp. CY327 and Rhabdobacter roseus DSM 105074. They were both homodimers with two identical subunits of approximately 45 kDa, and both showed the optimum pH and temperature at pH 8.0 and 40 degrees C, with the property of metal-independence. The melting temperatures (T-m) of Dyadobacter sp. and R. roseus MEases were 51.49 and 51.60 degrees C, respectively. The specific activity, K-m, k(cat), and k(cat)/K-m of Dyadobacter sp. MEase on D-glucose were 2.58 U/mg, 220 mM, 143 min(-1), and 0.65 mM(-1) min(-1), respectively, and those of R. roseus MEase were 2.42 U/mg, 178 mM, 104 min(-1), and 0.584 mM(-1) min(-1), respectively. Dyadobacter sp. and Rhabdobacter roseus (1 U/mL) produced 113.65 and 116.65 g/L of D-mannose from 500 g/L D-glucose at pH 8.0 and 40.C for 48 h, with the yield of 22.74 % and 23.33 %, respectively.