Identification, heterologous expression, and characterisation of β-1,3-xylanase BcXyn26B from human gut bacterium Bacteroides cellulosilyticus WH2

The cell walls of red and green algae contain beta-1,3-xylan, which is hydrolysed by the endo-type enzyme beta-1,3-xylanase. Notably, only marine-bacteria-derived beta-1,3-xylanases have been functionally characterised to date. In this study, we characterised the enzymatic properties of a potential beta-1,3-xylanase (BcXyn26B) derived from the human gut bacterium, Bacteroides cellulosilyticus WH2. The codon optimized BcXyn26B gene was synthesised and expressed in Escherichia coli BL21(DE3). The recombinant protein was purified by a two-step purification process using Ni-affinity chromatography followed by anion exchange chromatography, and its enzymatic properties were characterised. The recombinant BcXyn26B exhibited specific hydrolytic activity against beta-1,3-xylan and released various beta-1,3-xylooligosaccharides, with beta-1,3-xylobiose as the primary product. The optimum reaction temperature was 50 degrees C, higher than that for other enzymes derived from marine bacteria. This study represents the first report on the identification, heterologous expression, and characterisation of beta-1,3-xylanase from human gut microbes. Notably, the substrate specificity of BcXyn26B indicates that human gut Bacteroides species possess an unknown beta-1,3-xylan utilisation system.