Biosynthesis Of High Molecular Weight Poly(3-Hydroxybutyrate-Co-4-Hydroxybutyrate) Copolymer By Cupriavidus Sp. Usmaa1020 Using 1,8-Octanediol As The Carbon Precursor
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Date
2016-09
Authors
Ku Abdul Rahman, Ku Nur Elina Shaheeda
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Abstract
Polyhydroxyalkanoate (PHA) is a bacterial derived thermoplastic that is naturally biodegradable. Poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [P(3HB-co-4HB)] copolymer is a PHA known for its biocompatibility that can be transformed into biopharmaceutical products and be used in medical applications. High molecular weight polymer (>1 MDa) is highly desired for its many potential applications usage as 1,8-octanediol could produce high 4HB composition but low PHA concentration. This study investigates the potential of 1,8-octanediol to produce high molecular weight P(3HB-co-4HB) copolymer with improved PHA concentration using mixed substrate cultivation. One-stage cultivation process was performed using different carbon combination of 1,8-octanediol either with oleic acid, γ-butyrolactone, 1,4-butanediol or sodium 4-hydroxybutyrate. The effect of carbon to nitrogen (C/N) ratios of 1,8-octanediol was investigated and it was found that C/N=10 gave the optimum growth and PHA concentration. Biosynthesis of copolymer using different concentration of mixed-substrate by shake-flask cultivation resulted in 4 to 52 mol% 4HB monomer compositions by batch and fed-batch fermentation. Two selected mixed-substrate combination were studied in 3 L bioreactor. The combination of 1,8-octanediol with γ-butyrolactone was found to produce high molecular weight and elongation at break of 1060 kDa and 970%, respectively for P(3HB-co-22%4HB) copolymer while combination of 1,8-octanediol and sodium 4-hydroxybutyrate resulted in 643 kDa and 747%, respectively for P(3HB-co-28% 4HB). Feeding of carbon and nitrogen sources has enhanced the overall PHA concentration to 5.07
g/L. However, the molecular weight of copolymer decreased with increasing feeding rates. The molecular weight obtained through the feeding of 1,8-octanediol and γ-butyrolactone was similar to the results obtained from batch fermentation containing 1060 and 1052 kDa with improved overall residual biomass and PHA content. The elongation at break and molecular weight for single feeding of carbon was 944% for P(3HB-co-35%4HB) with 885 kDa and 840% for P(3HB-co-30%4HB) with 1052 kDa for twice the feeding of carbon sources. The copolymer was confirmed as alternating and random copolymers since the D values obtained were in the range of 0.2 to 1.0. This study showed that the combination of 1,8-octanediol and γ-butyrolactone can improve the production of P(3HB-co-4HB), and this discovery has the potential to enlarge the applications of high molecular weight copolymers in the biomedical fields.
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The potential of 1,8-octanediol to produce high molecular weight , using mixed substrate cultivation.