الفهرس 
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Abstract
Polyhydroxyalkanoates (PHAs) are microbial polyesters synthesized
by a variety of microorganisms as a temporary storage material of energy
and carbon. They are gaining more and more importance worldwide due to
their close analogy to plastics, biodegradability and biocompatibility.
PHB’s (poly-â-hydroxybutyrate, a kind of PHA) biodegradability makes
them extremely desirable substitutes for synthetic plastics.
In the present study, an attempt was made to isolate efficient PHB
producing bacteria from different agricultural soil samples. A total of 15
soil samples were collected, from which 180 bacterial isolates were
isolated. It was observed that out of 180 isolates, 45 isolates were found to
accumulate PHB. (twenty isolates from the sandy soil from Wady El-
Natron (WN). fifteen were isolated from South El Tahrir (ST) soils and ten
from Shalakan farm (SHF) soils. All the 45 PHB producers isolates were
subjected to quantitative estimation of PHB production. PHB yields varied
from 0.010 to 0.160 g/100 ml. Seventeen isolates were deeply black
coloured with (+++). Sixteen isolates were medium black coloured with
(++) and the rest were light black coloured with (+). Ten promising
bacterial isolates were selected based on their PHB yields. They were
WN10, WN2, WN11, WN4, ST15, SHF3, ST13, ST2, WN20 and WN12.
The culture parameters were optimized for all the 10 isolates, Glucose was
found to be the best carbon source for maximum PHB production by all the
isolates. Ammonium sulphate supplementation at 0.1% was found to be
optimum. Maintaining the pH of the medium at 7.0 was found optimum.
Maintaining the C:N ratio of 20:1 using the best C and N source was found
to be optimum.
Out of ten natural promising isolates, WN2 and WN4 were found to
be the most efficient PHB producers. Under optimized conditions, WN2
Abstract
produced a PHB yield of 19.75 g/ L after 132h while WN4 produced 19.16
g/L after 120h. WN2 performed better than the isolate WN4 according to
their PHB productivity. WN2 and WN4 were tentatively identified as
Stenotrophomonas (Pseudomonas) maltophilia and Pseudomonas putida
respectively, based on the morphological, biochemical tests and molecular
characterization. from the figure of time courses of cell growth and PHB
production, we can conclude that the best harvest time is 132h since at that
point the PHB production is highest, about 19.75g/L. Due to the exhaustion
of the medium components, intracellularly accumulated PHB could be
consumed by microorganism for its maintenance activities, so the PHB
productions begin to decrease at 138h in case of WN2 and 132h in case of
WN4. Scale up studies in 3L bottle fermenters were conducted under the
optimized conditions. Stenotrophomonas maltophilia produced a PHB
yield of 1.100g /100ml culture which is marginally higher than
1.033g/100ml culture produced by Pseudomonas putida. By this
experiment the PHB production of strain Stenotrophomonas maltophilia
was heightened greatly to 11.00g/L and Stenotrophomonas maltophilia’s
industrial application becomes more promising.
The numbers of PHB degrading microorganisms in natural
environments estimated by the clear-zone and film-MPN methods. The
numbers of PHB degrading microorganisms differed greatly depending on
differences in the natural surroundings. In infertile soil (Wady El-Natron
and South El-Tahrir), the numbers ranged between 4.33x103/g dry soil and
1.6x104/g dry soil, respectively while, in fertile soil (Shalakan Farm), the
number was 5.14x105/g dry soil.