A novel thermostable GH5_7 β-mannanase from Bacillus pumilus GBSW19 and its application in manno-oligosaccharides (MOS) production

A novel thermostable mannanase from a newly isolated Bacillus pumilus GBSW19 has been identified, expressed, purified and characterized. The enzyme shows a structure comprising a 28 amino acid signal peptide, a glycoside hydrolase family 5 (GH5) catalytic domain and no carbohydrate-binding module. The recombinant mannanase has molecular weight of 45   kDa with an optimal pH around 6.5 and is stable in the range from pH 5–11. Meanwhile, the optimal temperature is around 65   °C, and it retains 50% relative activity at 60   °C for 12   h. In addition, the purified enzyme can be activated by several ions and organic solvents and is resistant to detergents. Bpman5 can efficiently convert locus bean gum to mainly M2, M3 and M5, and hydrolyze manno-oligosaccharides with a minimum DP of 3. Further exploration of the optimum condition using HPLC to prepare oligosaccharides from locust bean gum was obtained as 10   mg/ml locust bean gum incubated with 10   U/mg enzyme at 50   °C for 24   h. By using this enzyme, locust bean gum can be utilized to generate high value-added oligosaccharides with a DP of 2–6.