Biochemical Properties of an Alkaline Xylanase From Bacillus Agaradhaerens C9 and Its Application in Producing Xylo-oligosaccharides With High Degree of Polymerization From Wheat Bran

Abstract

A xylanase of Bacillus agaradhaerens C9 was heterologously expressed and was then investigated. The recombinant xylanase (rBaxyl11) showed maximal activity at 60°C and pH 8.0-9.0. Under optimal conditions, Kcat of rBaxyl11 for arabinoxylan and glucuronoxylan were 599 s-1 and 330 s-1, respectively. rBaxyl11 showed a good stability at pH ranging from 5.0 to 9.0, and retained 50% of activity after 6-hour incubation at 70°C. However, it was markedly inactivated by transition elements including Fe3+, Ni2+, Mn2+, Co2+, Zn2+, Cu2+ and Fe2+. rBaxyl11 generated xylo-oligosaccharides (XOS) whose degree of polymerization (DP) is greater than 3 when hydrolyzing arabinoxylan, while the DP of XOS ranged from 2 to 6 when acting on glucuronoxylan. Simultaneously producing xylanase and XOS by recombinant E. coli containing rBaxyl11 were then carried out. Results showed that the engineering E. coli generated xylanase and high-DP XOS extracellularly using wheat bran as substrate, and concentration of XOS reached 73 mg/g substrate after 12-hour fermentation. This study indicates the feasibility of producing XOS by a single-step fermentation approach with low cost using rBaxyl11.