Discovery and characterization of endo-xylanase and β-xylosidase from a highly xylanolytic bacterium in the hindgut of Holotrichia parallela larvae

A highly xylanolytic bacterium, Sphingobacterium sp. HP455, was isolated from the hindgut of soil-dwelling Holotrichia parallela larvae. The endo-xylanase (Xyn455) gene of the glycoside hydrolase (GH) family 10 and β-xylosidase (Xyl455) gene of the GH43 family were cloned and expressed in vitro from this highly xylanolytic bacterium. Both the Xyn455 and Xyl455 enzymes acted on a broad range of hemicelluloses. Xyn455 cleaved xylan to liberate xylooligosaccharides (XOS), and the XOS were subsequently cleaved into xylose through the action of Xyl455. This synergistic action significantly increased the xylan hydrolysis to 62.8%, which is higher than the sum of hydrolysis achieved by the enzymes individually (26.65%). Furthermore, Xyl455 is a bifunctional enzyme with both β-d-xylosidase and α-l-arabinofuranosidase activities. Xyl455 also exhibits high xylose tolerance and a broad pH stability. The pH-dependent half-lives of Xyl455 range from 8.77 h to 43.52 h after pre-incubation for 1 h at 4 °C in buffers ranging from pH 3.0 to 9.0. These results suggest that both recombinant Xyn455 and Xyl455 and the bacterium are potential candidates to be used in commercial biomass conversion.