PoIi(3-hidroksibulirat-c0-4-hidroksibulirat) daripada bacteria pencilan tempatan
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Date
2007
Authors
Amirul AI-Ashraf Abdullah
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Abstract
A Gram negative bacterium, Cupriavidus sp. USMAA 1020 with an ability to produce poly(3-
hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] when grown on y-butyrolactone as the
sole carbon source was isolated from Malaysian environment. It accumulated P(3HB-co-4HB)
copolyester with a higher 4HB fraction (53 mol%) when grown in a nitrogen-free mineral medium
containing y-butyrolactone through a two-step cultivation process. The biosynthesis of P(3HB-co-
4HB) was also achieved by using 4-hydroxybutyric acid and alkanediols with even carbon numbers
such as 1,4-butanediol, 1,6-hexanediol, 1,8-octanediol, 1,1 O-decanediol, and 1, 12-dodecanediol.
The composition of copolyesters varied from 10 to 51 mol% 4HB, depending on the carbon sources
supplied. When y-butyrolactone was used as the sole carbon source, the 4HB fraction in
copolyester increased from 25 to 60 mol% as the concentration of y-butyrolactone in the culture
medium was increased. However, this lowered the P(3HB-co-4HB) content and molecular weight
significantly. Manipulating the culture conditions were affected the production of P(3HB-co-4HB)
and 4HB composition. P(3HB-co-4HB) copolymer with 4HB compositions ranging from 23 to 75
mol% 4HB were successfully produced by varying the medium aeration. The physical and
mechanical properties of P(3HB-co-4HB) copolymers were characterized by NMR spectroscopy,
gel-permeation chromatography, and tensile test. The number-average molecular weights (Mn) of
copolymers ranged from 260 x 103 to 590 X 103 Dalton, and the polydispersities (M~n) were
between 1.8 and 3.0. Increases in the 4HB composition lowered the molecular weight of these
copolymers. The P(3HB-c0-4HB) copolymers exhibit a wide variety of characteristics from
crystalline thermoplastic to strong elastomer when 4HB composition increases. In addition, the
increase in 4HB composition affected the randomness of copolymer, tensile strength, and
elongation to break.