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Abstract Marwa Salah Abdel-Hamid Ibrahim “Factors Affecting Cyst Formation of Azotobacter chroococcum for Its Application as a Biofertilizer” Unpublished doctoral of philosophy thesis, Menoufyia University, (GEBRI), department of Microbial Biotechnology, (2011). Beneficial free living soil bacteria especially Azotobacter chroococcum are widely spreading in Egyptian soil and usually referred to as plant growth promoting rhizobacteria (PGPR). Azotobacter sp. were isolated from different locations in Egypt and identified as Azotobacter chroococcum as their morphological and physiological properties according to Bergey’s Manual of Systematic Bacteriology. Species of Azotobacter are known to form heat and desiccation-resistance cysts that have a long life. Encystment in A. chroococcum can be induced by different methods i.e., butanol and ethyl alcohol as a sole carbon source. The cyst formation was detected by accumulation of poly-β-hydroxybutyrate, alginate formation, the morphology of vegetative and cyst forms were examined by cyst’s stain and electron transmission microscope. The resistance of cyst against different stress factors was investigated as the effect of heat resistance, pH range, NaCl tolerance and desiccation-resistance. Physiological characteristics of A. chroococcum such as acetylene reduction activity (nitrogenase enzyme) and production of some plant growth promoting substances such as Indole acetic acid (IAA), hydrogen cyanide (HCN) and siDROPhores production were also studied. Analysis with Random Amplified polymorphic DNA-Polymerase Chain Reaction (RAPD-PCR) was used to compare between the similarity pattern of the selected Azotobacter isolates and the reference strain and used as an identification tool of polymorphism. SDS-polyaclyramid gel electrophoresis (SDSPAGE) has been used to give the total protein pattern as a direct reflection of the gene expression of Azotobacter chroococcum under vegetative and cyst condition. Preservation and survival of vegetative and cyst forms of A. chroococcum in the liquid and carrier based inoculants through different periods was estimated. Evaluation of the effect of Azotobacter chroococcum under vegetative and preserved cyst liquid based inoculants as a biofertilizer on the growth of maize plants was studied. |