الفهرس 
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Abstract
The genetically engineered Bacillus subtilis DB100 (pSI) cells were immobilized by entrapment into Ca^ alginate. These bacterial cells harbour an extrachromosomal element called pSI plasmid. This plasmid carries the complete alkaline protease apr A gene and as a result cells carry this plasmid produce alkaline protease at high level.
In an attempt to monitor the gene expression and stability of the alkaline protease gene, free and Ca4’2 alginate - immobilized B. subtilis DB100 (pSI) cells were cultured in 2XSG medium at 37°C. It was noticed that the T^ (that is the time at which cells entered the stationary phase) of the Ca””2 alginate-immobilized cells was shifted by about two hours. This may be due to the reason that, the growth rate of immobilized cells is usually slower than that of free cells. On the other hand, the level of alkaline protease produced by either free and Ca”2 alginate-immobilized cells was similar. It should -be noticed here that liberated bacterial cells contributed to the production of alkaline protease. The stability of (pSI) plasmid of Ca^ alginate - immobilized cells^when grown on 2XNB medium without Kanamycin, was investigated. Plasmid stability reached 83% after 10 growth cycles when cultures were renewed every 24 hours (Segregational stability). It