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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Biofertilizer” Unpublished doctoral of philosophy thesis, Menoufyia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.