Biglari, Nazila
(2020)
Polyhydroxyalkanoates Production
By Cupriavidus Necator Mutants From
Glucose By Innovative Fermentation
Strategies.
PhD thesis, Universiti Sains Malaysia.
Abstract
Polyhydroxyalkanoate (PHA) is synthesized intracellularly by many
microorganisms and has potential as a biodegradable polymer. Due to the low
productivity and yield, only few microorganisms have been cultivated at industrial
scale to produce the PHA using natural and abundant carbon source. Cupriavidus
necator wild strain H16 can assimilate some simple sugars and oils but does not
utilize glucose. C. necator NSDG-GG and C. necator NSDG˗GGΔB1/pBPPccrMeJAc-
emd mutants are new strains developed to produce PHA from glucose. The
purpose of this study was to optimize the culture conditions to produce poly(3-
hydroxybutyrate) [P(3HB)] and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate)
[P(3HB-co-3HHx)] polymers by using these new mutants. Initially, appropriate
ranges of nutrients concentration (urea and glucose) were determined to obtain the
highest biomass and PHA by using the one-factor-at-a-time (OFAT) approach. Then,
a response surface methodology (RSM) was applied to optimize the key variables ata-
time to attain the optimal condition of biomass and PHA production in a
multivariable system. The optimized medium compositions which improved the
biomass and PHA production, were used to design fed-batch cultivation modes to
scale-up the biomass and PHA production in a 5 L bioreactor. Subsequently, a filland-
draw (F/D) fed-batch strategy was employed to understand the key parameters
that impacted the total cell densities and PHA concentration in the increment and
decrement fed-batch modes.
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