Biosynthesis And Characterization Of Novel Polyhydroxyalkanoate By Cupriavidus Necator PHB-4 Transformant Harboring PHA Synthase Gene Of Chromobacterium SP. USM2
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Date
2011-05
Authors
Ooi, Tin Fong
Journal Title
Journal ISSN
Volume Title
Publisher
Universiti Sains Malaysia
Abstract
The incorporation of a newly identified 3-hydroxy-4-methylvalerate (3H4MV)
monomer into the backbone of polyhydroxyalkanoate (PHA) is thought to improve
the properties of the resulting polymer. In this study, a transformant of C. necator
PHB¯ 4 harboring the PHA synthase gene of Chromobacterium sp. USM2 [C.
necator PHB¯4 (phaCCs)] was evaluated for its ability to synthesize novel short-chain
and medium-chain-length (SCL-MCL) PHA containing 3H4MV. Fructose or crude
palm kernel oil (CPKO) was used as main carbon source together with isocaproic
acid (4MV) as precursor to produce the excellent SCL-MCL PHA. 4MV
concentration and its feeding time had been identified as important parameters
affecting PHA content and monomer composition of the resulting polymer. A novel
PHA that consists of 78 mol % 3HB, 1 mol % 3HV, 3 mol % 3H4MV and 18 mol %
3HHx was obtained when 5 g/L CPKO and 1 g/L 4MV were fed during initial
inoculation. This PHA has a very interesting characteristic – rubber-like character
even after one year of aging. It can retract after being released from the stretching.
This property has not been found in any of the previously reported PHA. Another
transformant of C. necator PHB¯ 4 harboring the PHA synthase gene of Aeromonas
caviae [C. necator PHB¯4 (phaCAc)] was used as well for comparison of its ability to
produce PHA that contained different monomer compositions of 3H4MV. The novel
SCL-MCL PHA that was produced by C. necator PHB¯4 (phaCCs) was characterized
to further understand its excellent properties. Structural characterizations were
carried out by 1H NMR and 13C NMR spectroscopes while FT-IR was done to
confirm the presence of the functional groups of PHA. Besides, thermal properties
determined by TGA and DSC to compare these SCL-MCL PHA with P(3HB-co-
3HHx) copolymer showed that the incorporation of 3H4MV monomer and enhanced
3HHx monomer composition in the PHA have lowered the Tg, Tm and Hm. The
molecular weights of the polymers were in the range of 7 - 10 x 105. Mechanical tests
were also carried out. The tensile strength was in the range of 15 - 27 MPa,
Description
Keywords
Biosynthesis and characterization of novel polyhydroxyalkanoate , Cupriavidus necator PHB¯ 4 transformant harboring PHA