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OPTIMIZATION OF CULTURE CONDITIONS FOR THE PRODUCTION OF POLY (3-HYDROXYBUTYRATE) DEPOLYMERASE FROM NEWLY ISOLATED ASPERGILLUS FUMIGATUS FROM SOIL

ADIL FAROOQ LODHI, FARIHA HASAN, ZIAULLAH SHAH, ABDUL HAMEED, SHAH FAISAL AND AAMER ALI SHAH^*

Abstract: The present research work was aimed for the isolation and identification of poly (3-hydroxybutyrate) (PHB) degrading Aspergillus fumigatus and optimization of culture conditions for the maximum production of PHB depolymerase. This strain was isolated from the soil samples, collected from waste disposal sites, Islamabad, Pakistan, through enrichment and plate assay techniques, then culture conditions were optimized using enzyme assay, protein estimation and calculation of specific activity of the enzyme. The optimization experiments were done to determine the optimal combination of parameters, such as temperature, pH, substrate concentration, extra carbon sources and different inoculum sizes for maximum PHB depolymerase production by Aspergillus fumigatus. All the experiments were performed for 120hrs and samples were taken after every 24 hours and enzyme activities and protein concentrations were monitored. It was observed that maximum PHB depolymerase was produced at 45°C, pH 7 and 0.2% substrate concentration with specific activity 7.756U/mg, 6.120U/mg and 6.506U/mg respectively, after 24 hours of incubation. Lactose was found to be the most optimum source giving maximum specific activity 6.776U/mg as compared to fructose, sucrose and glucose. An inoculum size of 9% was found optimum for PHB depolymerase production with a maximum specific activity of 7.206U/mg after 24 hrs of incubation using lactose as an extra carbon source, pH 7, substrate concentration 0.2% and 45°C temperature. From the present study, it has concluded that the soil is a rich source of potential microorganisms, both bacteria and fungi, capable of degrading natural polymers.

Department of Microbiology, Faculty of Biological Sciences, Quaid-i-Azam University, Islamabad, Pakistan.