Biochemical characterization and sequence analysis of a xylanase produced by an exo-symbiotic bacterium of Gryllotalpa orientalis, Cellulosimicrobium sp HY-12

An exo-symbiotic bacterium capable of hydrolyzing xylan was isolated from the gut of the mole cricket, Gryllotalpa orientalis, and identified as Cellulosimicrobium sp. HY-12. The xylanase (XylA (CspHY-12)) of this organism bound tightly to both DEAE and mono Q resins, and its molecular mass (M-r) was about 39.0 kDa. The highest xylanase activity was observed at pH 6.0 and 60 degrees C. The enzyme was greatly suppressed by Ca2+, Cu2+, Co2+, and Fe2+ ions but not by Mg2+ and Mn2+. Although XylA (CspHY-12) was capable of hydrolyzing various types of xylosic compounds, it could not decompose carboxymethyl cellulose or xylobiose. The xylA (CspHY-12) gene consisted of an 1,188 bp open reading frame that encoded a polypeptide of 395 amino acids with a deduced molecular mass of 42,925 Da. The domain structure of XylA (CspHY-12) was most similar to those of the glycoside hydrolase (GH) family 10 endoxylanases. However its sequence identity with any of the enzymes in this family was below 52%. The results of this study suggest that the XylA (CspHY-12) is a new cellulase-free endo-beta-1,4-xylanase with some properties that are distinct from those of GH family 10.