الفهرس 
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Abstract
Fifty one bacterial isolates were isolated from Egyptian soil. These isolates were purified, and were examined for their ability to produce extracellular enzymes such as lipases, amylases, proteases and uricases. Four promising isolates were chosen based on their ability to produce lipolytic enzymes with significant level. These four isolates were abbreviated as 5, Ao, A72 and B72. After several rounds of screening, isolate 5 was selected as the promising lipase producing bacteria. Bacterial isolates were identified using biochemical tests as thermophilic Geobacillus. Further confirmation of biochemical characterization was carried out for isolate 5 utilizing 16S rRNA technique. Data were submitted to the GeneBank sequence database with a given accession number DQ923400. The bacterial isolate was identified as Geobacillus stearothermophilus.
Growth and extracellular lipase production were monitored for the above four isolates and it was found that, production of lipase started at late log phase and increased gradually till reached its maximal rate of production at the stationary phase. The level of extracellular lipase production from isolate 5 started at late log phase of the bacterial growth, about 6 hours after inoculation when the bacterial isolate was grown on PY or PY supplemented with olive oil. This level increased gradually with bacterial growth till reached its maximal level (48.51 U/ml) after 30 hours of inoculation on PY medium and (47.04 U/ml) on PY medium supplemented by 1% olive oil after 24 hours.
The effect of some cultural conditions on the bacterial growth as well as on the production of lipase was investigated to maximize lipase production from G. stearothermophilus 5. It was found that the presence of sugars (glycerol and glucose) induced the lipolytic enzyme formation in PY medium supplemented with CaCl2 at pH 7.0, inoculated with 4% of bacterial cells and incubated at 60ºC.
A sequential optimization approach based on statistical-mathematical experimental designs was applied to optimize the production of lipase from G. stearothermophilus 5. The first approach dealt with screening for cultural as well as nutritional factors affecting growth of G. stearothermophilus 5 with respect to lipase production. Plackett-Burman experimental design was applied to find out the most significant variables affecting enzyme production. Nineteen different factors (variables) including fermentation conditions and medium constitution were chosen to perform this optimization process. On the basis of the analysis of the regression coefficients of the 19 variables after 48 hours of incubation, Tween 80, K2HPO4, glycerol and glucose, were found to be the most significant variables affecting lipase activity. Those factors were chosen for further optimization. To improve the formula of the near optimum medium, on which optimization strategy could be preceded, four media have been tested. It has been shown that, medium M3 represent the most promising medium where maximum lipase activity was 511.33 U/ml and specific activity was 690.98 U/mg.