Production, purification and properties of a cellulase-free thermostable endoxylanase from newly isolated Paenibacillus sp. ASCD2

A newly isolated thermophillic strain of Paenibacillus sp. ASCD2 was studied for xylanase production under solid state fermentation. The influence of lignocellulosic substrates, moistening media, moisture ratio and pH was analysed; maximum xylanase production (343.52 U/g) was achieved on wheat straw with organic nitrogen rich medium (pH 7.0) at a moisture ratio of 1:5 (w/v) in 72 h at 50°C. After optimization, there was a 3.7-fold increase in xylanase yield. Ammonium sulphate fractionation followed by gel permeation chromatography yielded 16.59-fold purified xylanase with 38.33% recovery. The molecular weight of purified xylanase was found to be 20.2 kDa as estimated by SDS-PAGE. The optimum temperature and pH for xylanase activity of purified xylanase were found to be 60°C and 7.0, respectively. Kinetic parameters Km and Vmax were 2.5 mg/ml and 571 μmol mg−1 min−1, respectively. The enzyme was reasonably thermostable within the temperature range of 55 to 70°C. The half-life of xylanase was 415.12 min and 102.8 min at 65 and 70°C, respectively. Xylanase activity was significantly enhanced by Na+, Mg++ and K+ ions, strongly decreased by EDTA, Hg++, Cu++, Ag++ and Mn++ and unaffected by Fe++, Zn++, and Tween 80. The purified xylanase was found to be an endoxylanase as it produced only xylooligosaccharides from birchwood xylan.