Optimization of Conditions for the Secretion of Recombinant KG51 Xylanase by Bacillus subtilis

Xylanase (EC 3.2.1.8) is an enzyme that can hydrolyze xylan into short chains of xylose and xylo-oligosaccharide by cleaving β-1,4 glycosidic linkages. Xylanase is widely used in various industries. The aim of this study was to determine optimal incubation conditions for the secretion of recombinant KG51 xylanase by Bacillus subtilis with the response surface methodology (RSM). The four independent variables of induction time (0 to 32 h), isopropyl β-D-1-thiogalactopyranoside (IPTG) concentration (1, 2 and 5 mM), supplemental carbon source (sucrose, glucose, lactose, mannose and fructose) and supplemental nitrogen source (yeast extract, beef extract, tryptone, urea, NaNO3 and (NH4)2SO4 in an appropriate medium were individually tested using the one-variable-at-a-time method to determine the variables and coded level for RSM. Then, a central composite design-based RSM approach was used to identify and validate the optimized conditions with the four variables and five levels. The optimal xylanase production obtained in this study was 32.67 U/mL in the spent bacterial culture supernatant by using 2× YT broth supplemented with 1.79% sucrose and 0.73% yeast extract as extra carbon and nitrogen sources respectively, after induction with 0.98 mM IPTG for 23.34 h. The optimized conditions yielded approximately seven-fold higher xylanase levels than non-optimized conditions.