Secretion of recombinant thermo-alkali-stable endoxylanase of polyextremophilic Bacillus halodurans TSEV1 and its utility in generating xylooligosaccharides from renewable agro-residues

• First report on cloning and extracellular secretion of thermo-alkali-stable xylanase.
• Enhanced secretion of the recombinant xylanase was achieved by optimization.
• The recombinant xylanase have all the characteristic features of the native enzyme.
• The enzyme generates xylose-free xylooligosaccharides from agro-residues.

The recombinant thermo-alkali-stable endoxylanase (Bh-xyl) of polyextremophilic bacterium Bacillus halodurans TSEV1 has been produced extracellularly using a combination of cloning strategies and physico-chemical treatment of recombinant Escherichia coli cells. Sixty percent higher secretion of recombinant xylanase has been achieved by cloning Bh-xyl in pET28a(+) and expression followed by optimization of the cultural variables (EDTA, lysozyme and temperature). The pure recombinant endoxylanase is of 42 kDa, which is active in the broad pH and temperature ranges between 7.0 and 12.0, and 30 and 100 °C, with optima at 9.0 and 70 °C. The Km, Vmax and kcat values of the Bh-xyl (birchwood xylan) are 2.6 mg ml−1, 252.3 μmol mg−1 min−1 and 3.36 × 103 min−1, respectively. The enzyme has higher affinity for soft wood xylan than most of the xylanases from extremophilic microbes. The endoxylanase efficiently liberated xylooligosaccharides from the renewable agro-residues, which find application in functional foods as prebiotics.