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 β-1,3-xylan, which is hydrolysed by the endo-type enzyme β-1,3-xylanase. Notably, only marine-bacteria-derived β-1,3-xylanases have been functionally characterised to date. In this study, we characterised the enzymatic properties of a potential β-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 β-1,3-xylan and released various β-1,3-xylooligosaccharides, with β-1,3-xylobiose as the primary product. The optimum reaction temperature was 50 °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 β-1,3-xylanase from human gut microbes. Notably, the substrate specificity of BcXyn26B indicates that human gut Bacteroides species possess an unknown β-1,3-xylan utilisation system.