Full Length Research Paper

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

Silas B. Chidi¹, Busiswa Godana¹, Ignatious Ncube¹, Elbert Jansen Van Rensburg¹, Andrew Cronshaw² and Emil K. Abotsi¹*

¹Department of Biochemistry, Microbiology and Biotechnology, School of Molecular and Life Sciences, University of Limpopo, P. Bag X1106, Sovenga 0727, South Africa.

²EPIC Proteomics Facility, The University of Edinburgh, The Kings Buildings Edinburgh EH9 3JR, United Kingdom.

*Corresponding author. E-mail: emila@ul.ac.za. Tel: +27 15 268 2313. Fax: +27 15 268 3234.

Accepted 18 July, 2008

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 K_m and V_max values were 3.57 mg/ml and 55.5 μmol/min per mg protein, respectively. MALDI-TOF 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.

Key words: Aspergillus terreus, cellulase-free xylanase, purification, MALDI-TOF.