Generation of xylooligosaccharides from microwave irradiated agroresidues using recombinant thermo-alkali-stable endoxylanase of the polyextremophilic bacterium Bacillus halodurans expressed in Pichia pastoris

The recombinant Pichia pastoris harboring the endoxylanase gene (TSEV1xyl) of Bacillus halodurans TSEV1 yielded a high titer of extracellular xylanase (502 +/- 23 U ml(-1)) on induction with methanol. The purified recombinant xylanase (TSEV1xyl) displayed optimal activity at 80 degrees C and pH 9.0. The glycosylated recombinant xylanase exhibited higher thermostability (T-1/2 of 45 min at 80 degrees C) than the native enzyme (T-1/2 of 35 min at 80 degrees C). The agroresidues subjected to pretreatment (soaking in alkali followed by microwave irradiation) liberated xylooligosaccharides (XOS) upon hydrolysis with the recombinant xylanase. The removal of unhydrolyzed agroresidues, xylanase and xylose from the hydrolysate by two-step ultrafiltration led to the purification of XOS as confirmed by TLC as well as HPLC analysis. (C) 2014 Elsevier Ltd. All rights reserved.