Production and Characterization of Dextranase by Penicillium brevicompactum Isolated from Garden Soil

Abstract

Aim: The aim of the study is to produce and characterize dextranase produced by fungi isolated from soil and honey. Place and Duration of Study: The study was carried out at the Department of Microbiology, University of Ibadan, between April, 2017 and October, 2017. Methodology: Garden soils were collected from different locations within the University of Ibadan, Nigeria, and filtered and unfiltered honey from a local honey farmer. Serially diluted soil and honey samples were pour-plated on PDA for isolation of fungi. Isolated fungi were screened, then on dextran containing medium to select dextranase producing strains. Results: Forty two (42) fungi isolated from soil and honey was qualitatively and quantitatively screened for dextranolytic activity. Three moulds, Penicillium brevicompactum BG8, Fusarium oxysporum BG4 and Alternaria alternata DD5 were found to be the most potent dextranase producers with 18.01 DU/mL, 9.46 DU/ml and 8.26 DU/mL activities, respectively. Optimization of major parameters affecting enzyme production; including medium composition, pH, carbon (Temperature was not optimized at this stage) and nitrogen sources, substrate concentration revealed that maximum enzyme production was obtained when Pleszczynska medium was used for production. Penicillium brevicompactum BG8 and Alternaria alternata DD5 produced dextranase maximally at 1.0% dextran concentration with sodium nitrate and yeast extract as nitrogen sources at pH 5.5 at 30°C and 180 rpm for 5 days. Fusarium oxysporum BG4 produced dextranase maximally at 1.0% dextran concentration with sodium nitrate and yeast extract as nitrogen sources at pH 6.0 at 30°C and 180 rpm for 5 days. The production of dextranase by Penicillium brevicompactum, Fusarium oxysporum and Alternaria alternata increased to 65.41 DU/mL, 17.14 DU/mL and 20.10 DU/mL respectively when production was carried out using the best optimization conditions. Penicillium brevicompactum BG8 dextranase was purified to 14.1 fold homogeneity with an overall yield of 27% and an increase in specific activity from 2.67 – 37.68 U/g protein. Penicillium brevicompactum BG8 dextranase showed optimum activity at 50°C and pH 5.5, 2 mL substrate concentration and 1 ml enzyme concentration. Na+ ion activated dextranase while Cu2+ and Hg2+ ions completely inhibited the enzyme activity. Conclusion: Soil and honey are potential sources of isolation of dextranase producing organisms, particularly in higher quantities which may probably provide a way out to cheap and commercially available enzyme.