Abstract:
The antifungal activities of chitinases produced from Streptomyces species isolated from termitary and grassland soils at the research farm of the Federal University of Technology, Akure (FUTA), Nigeria were evaluated against some plant pathogenic fungi. Soil samples were collected from the above sites using hand trowel and Streptomyces were isolated by standard microbiological techniques. Screening for chitinase activity of Streptomyces species was done on a minimal synthetic medium supplemented with colloidal chitin as the carbon source. Production of chitinases was carried out in a chitinase production medium containing 1g colloidal chitin incubated at 30oC for 7 days. An optimum concentration of colloidal chitin for chitinase production was determined. Chitinase was purified from crude enzyme extract by single step gel filtration by Sephadex G-100. Chitinase produced by S. albus was purified by ammonium sulphate precipitation and further purified with ion exchange chromatography and gel filtration chromatography. Antifungal activities of crude chitinases was detected by agar well diffusion method. Thirteen Streptomyces species were isolated. Streptomyces species isolated from termitary were S. viridoflavus, S. griseus, S. galtieri, S. xanthophaeus, S. griseoflavus, S. albidoflavus and S. microflavus while those isolated from grassland soils were S. rimosus, S. albus, S. parvus, S. riseoflavus, S. fumosus S. spiraiis, S. flavogriseus and S. aureofaciens. Six of the Streptomyces species produced chitinase (S. griseus, S. flavogriseus, S. albus, S. albidoflavus, S. parvus and S. microflavus), but the highest production was obtained from S. albus. A high level of chitinase activity was observed in the culture medium with pH 6 at 30oC. Culture medium amended with maltose and ammonium sulphate served as good carbon and nitrogen sources for maximum production of chitinase. A high level of chitinase activity was observed in the culture medium supplemented with manganese. The purification yielded 69.15, 58.02 and 4.45 recovery with 1.37,
1.51 and 0.57 fold respectively. The purified enzyme from S. albus was characterized and the chitinase activity was found to be stable at temperature between 30oC and 40oC, and pH between 4.0 and 5.0. The enzyme was highly favoured by potassium chloride (KCL). Chitinases produced by Streptomyces species showed inhibitory effect against five phytopathogenic fungi (Magnaporthe oryzae, Fusarium graminearum, Rhizoctonia solani, Puccinia spp and Botrytis cinerea). It is therefore suggested that chitinases produced by Streptomyces species should be exploited as antifungal agents
