|Title:||Biosynthesis of polyhydroxyalkanoates in recombinant escherichia coli by using food industry wastes|
|Subject:||Polymers -- Biodegradation|
Organic wastes -- Recycling
Hong Kong Polytechnic University -- Dissertations
Department of Applied Biology and Chemical Technology
|Pages:||xiv, 104 leaves : ill. ; 30 cm|
|Abstract:||The higher production cost of PHAs has hampered the use of PHAs in daily life. But carbon source contributes 40% of production cost. Hence use of inexpensive carbon source can significantly reduce the cost of production. So this study was focused on the optimization of PHAs in recombinant E.coli XL-I by using food industry wastes. The plasmid pKS- that carries phaCAB genes and succinate degradation genes was constructed for P (3HB-co-4HB) production. But it could not produce the polymer. The recombinant E.coli XL-I that harboring the plasmid pKS-/phacCAB was also used for the production of P (3HB-co-4HB) when feeding 4-hydroxybutyrate and 1,4 butanediol as precursors. But P (3HB) content of 25.06 to 26.6 wt% was obtained when malt waste used as carbon source. It was lower than other experiments because of higher N content in the culture media. Part of this study, production of P(3HB-co-3HV) was optimized by using malt waste as carbon source. Higher OD (4.75) and PHA content (43.4wt%) were obtained at lower propionate (0.5g/l). But lower 3HV fraction (4.48mol%) was obtained. Higher 3HV fraction (13.33mol%) was obtained at lg/l of propionate concentration. In addition higher CDW was obtained at 30oC than 37oC. Even though higher PHA content was obtained at 37oC. Optimization was made by changing the temperature from 37oC to 30oC after 6 hours of fermentation. It yield higher CDW (1.72g/1) and higher PHA content (37.5wt %). Affect of feeding of propionate on polymer content and CDW was analyzed. Feeding of propionate at 0 hour could reduce the CDW(1.32g/1) but higher CDW (1.72 g/l) was obtained at 6 hours of fermentation. Even though feeding of propionate after 6 hours was reduced the 3HV fraction in PHAs. Higher OD(2.75g/l), PHA content (40.99wt%), Y(p/c)(0.2g/g) and 3HV fraction (11.75) was obtained in experiment 3 when the E.coli cells were grown at 37oC up to 6 hours and lg/l of propionate was added at 6 hours after that temperature was changed to 30oC. These optimized conditions were used for the production of P(3HB-co-3HV) in 101 fermentor. Faster growth was observed in the fermentor and higher PHA content (46.8wt), higher Yp/c (0.37g/g) and 3HV fraction (8.8 mol%) were obtained at 21 hours of the fermentation and PHA content decreased after 21 hours due to carbon limitation. Even though CDW was increased up to 33 hours of fermentation. Therefore, addition of carbon source at 21 hours of fermentation can significantly increase both polymer content and polymer concentration. Moreover use of food wastes can significantly reduce the cost of production of PHA and solve the solid waste management problem.|
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