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
