Purification and Characterization of a Thermostable Chitinase Produced by a Fungus Isolated from Fruit Tree Rhizosphere

This study reveals the chitinase producing ability of some fungi isolates cultured from the rhizosphere of different fruit trees such as mango, cassava, guava, and banana inside FUTA farm. A total of 16 isolates identified as Aspergillus nidulans, A. niger, A.flavus, A. fumigatus, A. ripens, Trichoderma viride, Mucor mucedo, Penicillium frequentans, Rhizopus stolonifer, Paecilomyces fumosoroseus, Gibbelula suffulfa and Geotrichum albidum were obtained and screened for chitinolytic activity. The effect of cultural conditions such as pH, temperature, metal ion, nitrogen source and carbon source was determined on Aspergillus nidulans, being the best chitinase producer. Further, the chitinase produced by Aspergillus nidulans was concentrated by ammonium sulphate precipitation and purified consecutively by gel filtration and ion-exchange chromatography. The optimum pH and temperature for chitinase activity and stability were examined as well as the effect of metal ions on the enzyme activity. The enzyme was most active at pH 7.0 and it was relatively stable at pH 4.0 - 9.0 retaining over 60% of initial activity after 120 min of incubation. The enzyme was most active at 50°C, possessing high thermal stability at high temperature of 70°C. The purified chitinase was significantly inactivated at 80°C and almost completely at 90°C when it was pre-incubated at these temperatures for 60 min. The enzyme was strongly inhibited by FeSO4, ZnCl2 and MnCl2 and was less sensitive to CaCl2 and KCl. This purified Aspergillus nidulans chitinase can be used as a catalyst for the degradation of chitin-containing compounds.