الفهرس 
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Abstract
Total of forty five and one hundred microbial isolates were isolated from various soil samples of different localities at Sharkia Governorate, Egypt. Among them 29 isolates represented by actinomycete and 116 isolates of bacteria. The isolate No. 47 was selected as the most potent for vitamin B12 biosynthesis, and was identified as Pseudomonas syringae producing 15.9 µg/mg protein. Determination of vitamin B12 biosynthesis was carried out by microbiological assay using E.coli (ATCC 14169) mutant vitamin B12 auxotroph strain as the test micro-organism that possessed absolute requirement for vitamin B12. Optimization studies revealed that, an incubation period of 48 hour was found to be the maximal vitamin B12 biosynthesis at pH, 7.0 and 35oC under shaking condition (140 rpm). The basal medium was used for studying the most favorable condition for vitamin B12 production. Among the tested carbon sources, glucose at concentration of 4.0% was suitable for maximum growth content and vitamin B12 biosynthesis by the selected isolate. Different nitrogen sources were tested by adding nitrogen sources in the basal medium. In the presence of yeast extract 1.5 g/l Phosphate salt exerted stimulatory effect on growth content and vitamin B12 biosynthesis by tested organism. K2HPO4 at a concentration of 2.5 g/l. FeSO4 .7H2O as a microelement the optimal level appeared be 0.02 g/l. Plant growth hormones, (2,4-D dichlorophenoxy acetic acid), (naphthalene acetic acid, NAA), (kinetin (KN) and Gibberellin (GA3) were tested for their effect in vitamin B12 biosynthesis by Pseudomonas syringae. Vitamin B12 was increased in presence of these phytohormones at the optimum concentrations of these phytohormones at 8.0, 2.0, 14& 3.0 mg/l, respectively. Also, addition of 2.0 mg/l of salisylic acid, was optimum for maximal production of vitamin B12.