Production, purification and characterization of celullase-free xylanase from Aspergillus terreus UL 4209

Abstract

Aspergillus terreus, UL 4209 strain, isolated from the soil in South Africa was used to produce an extracellular cellulase-free xylanase in shake flask cultures containing oat spelt and/or birchwood xylans. Maximum xylanase activity (35 U/ml) was observed after 96 h at 35oC and pH 6 in 1% oat spelt xylan. The xylanase was purified to homogeneity by gel filtration on Sephacryl S-200. This enzyme was found to be a single subunit protein of 22 kDa showing optimal activity at 35oC and pH 6. The enzyme retained 95% activity at 35 - 40oC after 4 h incubation at pH 6 and at 50oC the half-life was 5.8 h. The apparent Km and Vmax values were 3.57 mg/ml and 55.5
mol/min per mg protein, respectively. MALDITOF and LC mass spectroscopy gave 8 peptide ions whose sequence alignments showed that the xylanase produced by this strain has homology with those of other Aspergillus strains such as A. terreus and A. versicolor. These observations showed that our strain produced a low molecular weight, acidophilic, and thermostable xylanase that may be considered for processes operated at moderate temperatures and pH such as preparation of baked cereal food, clarification of fruit juices and saccharification of agro-residues.