β-Mannanase BoMan26B from Bacteroides ovatus produces mannan-oligosaccharides with prebiotic potential from galactomannan and softwood β-mannans

Galactomannan (GM) in legumes and acetyl-galactoglucomannan (AcGGM) in softwoods are wide-spread 13-mannans. Their depolymerisation is catalyzed by 13-mannanases. We have investigated a cell-surface exposed and galactose-tolerant 13-mannanase (BoMan26B) from the abundant gut bacterium Bacteroides ovatus. Glycosidases from the gut microbiota have potential for production of prebiotics, such as dietary saccharides that would promote beneficial bacteria in the gut. BoMan26B was explored for production of potential prebiotics. Using the above 13-mannans as substrate we investigated the product profiles using a herein developed new high-resolution anion-exchange chromatography procedure. The produced linear and galactosyl-decorated 13-mannan-oligosaccharides (MOS/GMOS) were mainly of degree of polymerization (DP) 2-6, consistent with the glycan-binding subsites of BoMan26B. Some GM and AcGGM products were acetylated. DP 2-6 MOS were produced at a yield of 30 and 33% (w/w) from GM and AcGGM, respectively. In addition, about as much DP 2-6 GMOS were produced, assessed using guar a-galactosidase as analytical aid. Growth studies using the human gut bacteria Bifidobacterium adolescentis ATCC 15703 (acetate producer) and Roseburia hominis DSMZ 6839 (butyrate producer) revealed significant differences in utilization of specific MOS/GMOS. The prebiotic potential of the MOS/ GMOS generated by BoMan26B was further underlined by the observation that both bacterial strains produced short-chain fatty acids.