الفهرس 
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Abstract
In this study, 29 thermophilic bacterial isolates were isolated from the local hot spring Hammam Pharaon in Sinai which is advised the hottest sulfuric hot spring in Egypt with temperature ability to 70ºC. Among these isolates, only four different bacterial strains were selected for this study due to the ability to produce thermostable enzymes. These isolates, were abbreviated as HF 84, HF 85, HF 86 & HF 87, from the morphologically, biochemically and physiologically characterization ,the four strain were found to be gram positive bacilli and to be different species due to different biochemical characters. The optimum growth of isolate (HF84) was recorded with range at pH 6.6-8 and temperature 64-72°C. The optimum growth of isolate (HF85) was recorded with range at pH 6.2-8.2 and temperature 60-75°C. The optimum growth of isolate (HF86) was recorded with range at pH 5.5-8 and temperature 56-67°C. Finally, the optimum growth of isolate (HF87) was recorded with range at pH 6-7.5 and temperature 60-70°C. These four isolates were molecularly identified by obtaining and analyzing the sequence of their 16S rRNA gene. The data obtained for the optimum temperature agrees well with the data collected about the temperature and pH of the site of collection supporting that the obtained isolated are thermophilic bacillus (Geobacillus) adapted to live under the conditions of Hammam Pharaon. The strain HF 84 was most closely related to Geobacillus caldoxylolyticus, The strain (HF 85& HF 86) showed very high sequence identity to Geobacillus thermoglucosidasius and the strain HF 87 showed high sequence similarity to Geobacillus vulcani and the four strains were submitted to GenBank with accession numbers; KY084244 ,MF155645, MF155646, and MG564474 respectively.