Production and biochemical characterization of partially purified cellulase-free, thermo-acidophilic endoxylanase from Lysinibacillus fusiformis strain TB7 using kolanut husk as feedstock

Abstract

Xylanases have become very important enzymes in many industrial processes for the valorization of xylan-rich lignocellulosic wastes. Here, some physicochemical and kinetic properties of a purified endoxylanase produced on kolanut husk-based medium by Lysinibacillus fusiformis are presented. The crude enzyme solution was first subjected to precipitation with solid ammonium sulphate and further purified on DEAE-Sephadex A-50 anion-exchange and Sephadex G-100 gel filtration columns chromatography prior to biochemical characterization. The purified endoxylanase was 21 kDa as determined by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) and was thermostable, exhibiting optimum activity at 60 °C and pH 5.0. The Km and Vmax were respectively estimated to be 29.5 mg/ml and 125 μmol/min/ml using Birchwood xylan as substrate. Activity of the enzyme was enhanced by Na+, Ca2+, Mn2+, Mg2+ and K+ at concentration of 5 mM but inhibited by Hg2+, Cu2+, Pb2+, Fe3+, EDTA, SDS and Urea. The purified endoxylanase showed high hydrolytic activity on Birchwood xylan and kolanut husk but extremely poor or no activity on carboxymethyl cellulose, starch or pectin. This L. fusiformis strain TB7 endoxylanase has desirable properties useful for biotechnological applications in laundry, fuels, feeds, paper and pulp industries.