الفهرس 
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Abstract
The main objective of this study was the isolation of fungi inhabiting different sites of poultry wastes and find out the optimum conditions for uricase production by some fungi isolated from poultry waste. Purification of the enzyme and determination of its physic-chemical properties are carried out. The results obtained during studies are summarized in the following points : 1. Five genera were isolated from different samples collected from different poultry farms in Mansoura district. The isolates were identified as Aspergillus flavus, Aspergils terreus, Aspergils Niger, Penicillium chrysogenm, Trichoderma sp., Rhizopus nigricans and Mucor spinosus. They were screened for their potentialities for uricase production by uricase plate assay method on uric acid medium. After incubation, the formation of clear zone around the fungal colony indicating its potentiality for uricase production. 2. The uricase activities in liquid media containing uric acid were 7.5 U/ml for Aspergillus flavus, 4.5 U/ml for Aspergills terreus and 2.6 U/ml for Trichoderma sp. 3. Statistical screening using Box-Behnken design with 27 runs was applied to screen four factors for their significance on uricase production by Aspergillus flavus. The optimal levels and interaction effect of these variables were further optimized. The result showed that the optimum temperature for fungal growth and uricase production by Aspergillus flavus was 40 °C, the maximum production of uricase and biomass yield were recorded at pH 6.5. 4. The fungal biomass and the enzyme yield were achieved in the medium supplemented with 10 g/l sucrose as a carbon source for Aspergillus flavus. Addition of NH4NO3 with 17.5 g/l to the media as a nitrogen source gives the maximum production of uricase. 5. The crude enzyme extract of Aspergillus flavus was partially purified using ammonium sulfate and dialysis. Both purified and crude enzyme were added to sample of poultry waste separately which indicate that purified enzyme has high activity in compared with the crude enzyme. In conclusion, Aspergillus flavus can be considered as a source for the production of extracellular uricase that can be used in different applications instead of chemical applications which create environmental pollution.