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Microbial synthesis of
poly(3-hydroxybutyrate-co-4-hydroxybutyrate)
copolymer by Cupriavidus sp. USMAA2-4 through
a two step cultivation process
Hui-Ling Chai1, Rahayu Ahmad1, A.
R. M. Yahya1, M. I. A. Majid2 and A.
A. Amirul1,2*
1School
of Biological Sciences, University Sains Malaysia, 11800
Penang, Malaysia.
2Malaysian
Institute of Pharmaceuticals and Nutraceuticals, MOSTI,
Malaysia.
*Corresponding author. E-mail:
amirul@usm.my Tel.:
604-6533888 ext 4013.
Fax:
604-6565125.
Accepted 30
June, 2009 |
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A Gram negative bacterium, Cupriavidus sp.
USMAA2-4
was isolated from a soil sample in Northern Peninsular of
Malaysia and was able to synthesize polyhydroxyalkanoate
containing 4-hydroxybutyrate unit when grown on
g-butyrolactone
as the sole carbon source. The polyester was purified from
freeze-dried cells and analyzed by nuclear magnetic
resonance (NMR) spectroscopy. 1H and 13C
NMR results confirmed the presence of 3HB and 4HB monomers.
The isolated strain has the ability to synthesize
poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)]
in a two step cultivation process on a medium containing
g-butyrolactone
as the carbon source. A high fraction of 4HB monomer unit
was obtained by manipulating the cell concentration, types
of carbon sources and carbon source concentration in the
cultivated medium. On the basis of the PHA composition, we
suggest that carbon sources such as 1,6-hexanediol,
1,8-octanediol, 1,10-decanediol and 1,12-dodecanediol
resulted in a skewed PHA composition. On the other hand, the
molar fraction of 4HB in P(3HB-co-4HB) was increased
significantly from 25 – 51 mol % by the higher concentration
of
g-butyrolactone
as the sole carbon source in the medium. The molecular
weight and thermal properties of P(3HB-co-4HB) were
revealed by gel permeation chromatography (GPC) and
differential scanning calorimeter (DSC), respectively. We
found that this bacterium is able to produce wide range
copolymer with the number-average molecular weights (Mn)
of copolymers ranging from 17 x 103 to 412 x 103
Dalton. Increase in the concentration of
g-butyrolactone
lowered the molecular weight of these copolymers.
Higher concentration of
g-butyrolactone
also resulted in more branched polymer and consequently gave lower values for both the glass transition temperature (Tg)
as well as melting temperature, Tm.
Key
words:
Biopolymer, polyhydroxyalkanoates, poly(3-hydroxybutyrate-co-4-hydroxybutyrate),
biosynthesis, characterization. |
