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Titre : Characterization of Extremophilic Bacteria Isolated from Egyptian Salt Lakes

Auteur : Ahmed Hassan Korany Ramadan

Université de soutenance : Cairo University

Grade : Master of Science (MS) 2015

Résumé
Egyptian aquatic bacetrioplankton is of highly positive impact due to the various aquatic systems of this country. Although the bacterial community found in the seawater with its salty nature may be different from those of freshwater in rivers and lakes, most of those areas are still untapped. Water samples from different Egyptian aquatic environments (Red Sea, Alexandria Saltern and Lakes of Wadi EL Rayan, Wadi AL Natrun and Qarun) were screened for extremophilic bacterial strains using different modified cultivation media. The aim of this work was to isolate novel useful extremophilic bacterial strains with various enzymatic activities that may allow their use in industrial, agricultural and biotechnological fields. Eighty isolates were obtained including 69 bacterial isolates and 11 fungal ones. The isolates showed great variation in their pH and salt requirements and hence they could be categorized into four different groups ; moderately halophilic (10% NaCl & pH 7), extremely halophilic (22.5% NaCl & pH 7.5), haloalkaliphilic (10% NaCl & pH 9) and alkaliphilic (0% NaCl & pH 8.7). Upon testing their enzyme production capability, they showed cellulase, amylase and DNase activities in 51.25 %, 46.25% and 26.25% of the isolates ; respectively, but no lipase activity was observed. The combined hydrolytic activity was characteristic for several isolates. Production of cellulase enzyme was predominant among the tested isolates either as pure cellulase (6.25% of all isolates) or combined (45% of all isolates) with other enzymatic activities. Nineteen strains were found to produce specific cellulase activity up to 44.46 U/mg and the highest three isolates (AS4, RSS-1 and QLS-3.1) were subjected to further optimization of their culture conditions in order to identify the most significant factors affecting their cellulase production. In this respect, a Plackett Burman experimental design was constructed using ten factors (time, temperature and pH of fermentation, inoculums size of isolates, one carbon source (Carboxy methylcellulose) and two different nitrogen sources : organic source (yeast extract) and inorganic source (ammonium sulfate) and different salts concentrations (sodium chloride, ZnSO4 and Calcium/Magnesium ratio). Each one of these factors had two levels : high level (+1) and low level (-1). The conducted optimization design identified different factors to significantly affect cellulase production. These factors contributed to about 2, 3.5 and 7.6-fold increase in cellulase productivity for the three isolates (RSS-1, AS4 and QLS-3.1) ; respectively. Those isolates were molecularly identified, using 16s rRNA sequencing, as Halovibrio spp. (AS4) and Halobacillus spp. (RSS-1 and QLS-3.1). Few studies have reported the isolation of haloalkaliphilic bacterial strains from Qarun lakes and Alexandria Saltern while to the best of our knowledge, the microbial diversity of Wadi El Rayan has not been studied before.

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