Optimization of the extracellular secretion of black goat rumen metagenome-derived KG42 xylanase by Bacillus subtilis

Abstract

Xylanase (E.C. 3.2.1.8) is the enzyme that breaks down β-1,4 xylan by cleaving β-1,4 glycosidic linkages. Production of xylanases is important for various industrial applications. Here, we aimed to determine the optimal incubation conditions for expression and secretion of KG42 xylanase in Bacillus subtilis using response surface methodology based on Box-Behnken design in preparation for industrial applications. Among nine broth media tested in this study, Power Broth was chosen as a basal medium. In addition to the basal medium, the four other independent variables of extra carbon sources (glucose, lactose, mannose, fructose, and sucrose), extra nitrogen sources (beef extract, yeast extract, tryptone, urea, NaNO3, and (NH4)2SO4), isopropyl β-D-1-thiogalactopyranoside concentrations, and induction times were individually tested using one factor at a time in an optimization experiment. Next, a Box-Behnken design-based response surface methodology approach was used to identify and validate the optimized incubation conditions with the four variables in batch culture. The statistically optimized incubation conditions obtained from this study yielded a maximum of approximately 3- to 4-fold increases in the expression and secretion of KG42 xylanase by B. subtilis in comparison with unoptimized medium and incubation conditions.