Partial purification and characterisation of a xylanase enzyme produced by a micro-organism isolated from selected indigenous fruits of Zimbabwe

Aerobic bacteria and fungi isolated from Ziziphus mauritiana, Scierocarya birrea fruits and a cattle compost were screened for production of endo-xylanase enzyme. Xylanolytic activity was found in 10 of the 88 isolates obtained. Two best endo-xylanase enzyme producers (SB-9a and TC-17d) were selected for further investigations. The two isolates were classified as belonging to the genus Bacillus. The endo-xylanase enzymes from both isolates were optimally active at pH 8 and stable over a pH range of 6.0–9.0. The optimum temperature for xylanase activity, assayed at pH 8 was 60°C. The endo-xylanase from isolate SB-9a was stable at 50°C, maintaining over 50% of its activity for 1 h at pH 8. The endo-xylanase from isolate TC-17d was less stable, maintaining about 20% of its activity for 20 mm at 50°C and pH 8. Endo-xylanase activity for isolate SB-9a was inhibited by Hg2+, Ag+ and Mn2+ ions while Fe3+, K+, Nat, Ca2+, and Cu2+ ions stimulated xylanase activity. The endo-xylanase enzyme from isolate SB-9a was partially purified by ammonium sulphate precipitation, and gel filtration chromatography. It had a specific activity of 308 nkat/mg protein. This enzyme could have potential uses in biotechnological applications such as in pulp, paper and food manufacture due to its high specific activity and alkaline pH optima.