Novel alkali-tolerant GH10 endo-β-1,4-xylanase with broad substrate specificity from Microbacterium trichothecenolyticum HY-17, a gut bacterium of the mole cricket Gryllotalpa orientalis

The XylH gene (1,167-bp) encoding a novel hemicellulase (41,584 Da) was identified from the genome of Microbacterium trichothecenolyticum HY-17, a gastrointestinal bacterium of Gryllotalpa orientalis. The enzyme consisted of a single catalytic domain, which is 74% identical to that of an endo-β-1,4-xylanase (GH10) from Isoptericola variabilis 225. Unlike other endo-β- 1,4-xylanases from invertebrate-symbiotic bacteria, rXylH was an alkali-tolerant multifunctional enzyme possessing endo-β-1,4-xylanase activity together with β-1,3/β-1,4- glucanase activity, which exhibited its highest xylanolytic activity at pH 9.0 and 60°C, and was relatively stable within a broad pH range of 5.0-10.0. The susceptibilities of different xylosebased polysaccharides to the XylH were assessed to be as follows: oat spelts xylan > beechwood xylan > birchwood xylan > wheat arabinoxylan. rXylH was also able to readily cleave p-nitrophenyl (pNP) cellobioside and pNP-xylopyranoside, but did not hydrolyze other pNP-sugar derivatives, xylobiose, or hexose-based materials. Enzymatic hydrolysis of birchwood xylan resulted in the product composition of xylobiose (71.2%) and xylotriose (28.8%) as end products.