ANTIFUNGAL ACTIVITIES OF CHITINASE PRODUCED BY MICROORGANISMS FROM RHIZOSPHERE OF SOME PLANTS AND FISH POND SEDIMENTS IN AKURE

Abstract

Microorganisms (bacteria and fungi) were isolated from the rhizosphere of different fruit trees such as mango, cassava, guava, banana and fish pond sediment located at the research farm of the Federal University of Technology, Akure (FUTA), Nigeria. The total number of microorganisms isolated were 27, comprising 11 bacteria and 16 fungi. These isolates were screened for chitinase activity on minimal synthetic medium supplemented with colloidal chitin as the carbon source. All the isolates produced chitinase, but the highest production was obtained from Serratia marcescens and Aspergillus niger. Antifungal activities of crude chitinases produced were determined against five plant pathogenic fungi (Marchophominia phaseolina, Rhizoctonia solani, Fusarium oxysporum, Colletotrichum lindemuthianum, Fusarium solani). Chitinases from selected bacterial isolates showed antagonistic effect against all the pathogenic fungi. Chitinases from Geotrichum albidum, Aspergillus niger and Aspergillus flavus showed antagonistic effect against all the pathogenic fungi except chitinases from Trichoderma viride and Aspergillus fumigatus which could not inhibit the growth of F. solani, M. phaseolina and R. solani. The effect of environmental factors such as pH, temperature, metal ion, nitrogen source and carbon source were determined on S. marcescens and A. niger. Temperature of 40οC, pH of 8.0, glucose, ammonium nitrate and calcium ion favoured the maximum production of chitinase by Serratia marcescens. Temperature of 50οC, pH of 8.0, sucrose, ammonium sulphate and manganese ion was favourable for maximum chitinase production by Aspergillus niger. Chitinase produced by S. marcescens and A. niger were purified by ammonium sulphate (60%) precipitation and purified consecutively with ion-exchange chromatography and gel filtration chromatography. Chitinase produced by Serratia marcescens was purified 1.80, 4.32 and 6.05 fold with a recovery of 61.41%, 53.93% and 37.69%. Chitinase produced by Aspergillus niger was purified 1.90, 3.70 and 8.86 fold with a recovery of 19.20%, 16.04% and 9.74% .The purified enzyme from S. marcescens and A. niger were characterized. S. marcescens and A. niger were identified through 16S rRNA gene sequencing, and it showed 99% and 97% similarity with Serratia marcescens (CP003960.1) and Aspergillus niger (AY727901.1) respectively. Chitinase could be used as biological control agent