الفهرس 
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Abstract
.1.1. Taxonomy and ecology
Bacillus subtilis is a Gram-positive, spore-forming bacterium. It is commonly found in soils and on plant materials and grows aerobically at intermediate temperatures and pH (Claus and Berkeley, 1986). B. subtilis is a fast growing, non-fastidious and is considered an opportunistic microorganism with no pathogenic potential to humans (Sharp et al, 1989).
As with many other bacilli, B. subtilis secretes substantial amounts of proteins, especially hydrolytic enzymes such as amylases and proteases (Priest, 1977). Most of these extracellular proteins are produced post- exponentially as a result of carbon, nitrogen or phosphorous starvation (Schaeffer, 1969; Sonenshein, 1989; Fisher and Sonenshein, 1991).
The genetics of B. subtilis strain 168 has been extensively studied, making it the best characterized Gram-positive bacterium (Burkholder and Giles, 1947; Losick et al, 1986; Ferrari and Hoch, 1989). Therefore, this organism has been recommended for several industrial applications (Debabov, 1982). It is often referred to as a non-pathogenic bacterium and it is even consumed by humans in large quantities in the Japanese food natto (Djien and Hesseltine, 1979.