A Novel GH26 β-Mannanase from Bacillus subtilis HM7 Producing Manno-Oligosaccharides with Strain-Specific Prebiotic Activity.

Mannan-oligosaccharide (MOS) produced from the hydrolysis of mannan by β-mannanase, demonstrate several beneficial properties, such as prebiotic and modulation of tight junction activity. In this study, two novel GH26 β-mannanases, MAN26HM7/A and MAN26HM7/B, from Bacillus subtilis HM7 were cloned and expressed in Escherichia coli BL21 (DE3). The optimal pH and temperature of MAN26HM7/A and MAN26HM7/B were pH 5.0 and 40 °C, and pH 6.0 and 60 °C, respectively. The β-mannanases from Bacillus subtilis HM7 exhibited different MOS product patterns from DP2-DP6 oligo-mannose. MAN26HM7/A and MAN26HM7/B preferentially hydrolyzed substrates with more than five mannose residues. The amino acid residues, A146, F65, and H331 surrounding the active sites of MAN26HM7/A and MAN26HM7/B were compared with those of other β-mannanases from Bacillus species. These amino acid differences may be responsible for altered substrate binding, substrate specificity, and hydrolytic product pattern of MAN26HM7/A and MAN26HM7/B. MOS produced from konjac, copra meal and green coffee bean by MAN26HM7, MAN26HM7/A, and MAN26HM7/B were tested for prebiotic activity. MOS produced from coffee bean hydrolyzed by MAN26HM7/B exhibited the highest prebiotic activity score on Lacticaseibacillus rhamnosus GG (ATCC 53103). This study provides an understanding of the characteristics, hydrolysis pattern of the novel GH26 β-mannanases, and the application of these novel GH26 β-mannanase for prebiotic production from agricultural products.