| 1. |
- Doan Van, Thuoc, et al.
(författare)
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Ectoine Production by Halomonas boliviensis: Optimization Using Response Surface Methodology.
- 2010
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Ingår i: Marine Biotechnology. - : Springer Science and Business Media LLC. - 1436-2236 .- 1436-2228. ; 12, s. 586-593
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Tidskriftsartikel (refereegranskat)abstract
- Two cultivation steps were used for production of biomass and ectoine by Halomonas boliviensis, respectively. The optimization of some nutrient parameters in each step was investigated by using response surface methodology. Twenty and 12 experiments were performed to attain optimal conditions for biomass and ectoine production, respectively. The model predicted a maximum biomass concentration of 3.34 g/L on optimization of NH(4)Cl, K(2)HPO(4), and MgSO(4)*7H(2)O concentrations during the first cultivation, while a maximum ectoine concentration of 1.27 g/L was predicted on optimizing NaCl and monosodium glutamate concentrations in the second cultivation. The experimental values obtained (3.36 g biomass/L and 1.25 g ectoine/L) were in good agreement with the predicted values. The optimized conditions were also used for two-step 1.5-L fed-batch fermentations. In the first step, biomass concentration of 28.7 g/L was obtained while in the second step biomass concentration increased to 63 g/L. Ectoine concentration of 9.2 g/L was obtained, and the overall ectoine productivity was 6.3 g/L/day, being among the highest reported so far.
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| 2. |
- Doan Van, Thuoc, et al.
(författare)
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High productivity of ectoines by Halomonas boliviensis using a combined two-step fed-batch culture and milking process.
- 2010
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Ingår i: Journal of Biotechnology. - : Elsevier BV. - 1873-4863 .- 0168-1656. ; 147:1, s. 46-51
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Tidskriftsartikel (refereegranskat)abstract
- A process comprising two-step fed-batch cultivation has been investigated for the production of ectoines using the halophilic bacterium Halomonas boliviensis DSM 15516(T). The first cultivation was performed under optimal conditions for cell growth and resulted in cell mass concentration of about 41gl(-1) after 24h of cultivation. During the second cultivation at higher salt concentration, accumulation of ectoines increased while cell mass decreased with increasing salt concentration. Maximum productivity of total ectoines reached was 10gl(-1)d(-1) with ectoine concentration of 6gl(-1) and hydroxyectoine concentration of 8gl(-1) after 9h of cultivation at 18.5% NaCl, which is among the highest reported so far. H. boliviensis cells were further recycled for the production process after releasing the ectoines. About 75% of the accumulated ectoines were released by subjecting the cells to hypoosmotic shock. On subsequent reincubation in a medium containing higher salt concentration the cells were able to re-synthesize the ectoines resulting in a global productivity of 11.1gl(-1)d(-1), and ectoine and hydroxyectoine productivities of 9.1gl(-1)d(-1) and 2.0gl(-1)d(-1), respectively.
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| 3. |
- Guzmán, Hector
(författare)
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Production of Ectoines and Poly(3-Hydroxybutyrate): High Cell-Density Cultivation of Halomonas Boliviensis
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis reports a study involving the use of Halomonas boliviensis, a moderate halophile, for production of biopolyester poly(3-hydroxybutyrate) (PHB) and compatible solutes ectoine and hydroxyectoine through high cell-density cultivation comprising fed-batch cultures. PHB is a biodegradable plastic produced by bacteria as energy reserve and can potentially be used as a replacement of fossil based plastic. Ectoines comprise osmoprotectants and find use as stabilizers of cells and biomolecules. High PHB content and volumetric productivity were achieved by fed-batch culture of H. boliviensis using an optimized medium with glucose as carbon source. Cell growth was favored in the initial phase of cultivation by providing sufficient nutrients to the fermentor. Nitrogen and phosphorus feed was then limited to trigger PHB accumulation. This resulted in a cell dry weight, PHB content and volumetric productivity of 44 g L-1, 81 wt% of the cell dry weight and 1.1 g L-1 h-1, respectively. Further optimization of the feeding strategy was studied in two-stage fed-batch cultivation. Prolonged feeding of nutrients during the first stage and subsequent nutrient limitation increased the cell dry weight to 91 g L-1 but lower PHB content than in previous studies. However, the volumetric productivities achieved were slightly improved and are comparable to the highest values reported so far. Two-step fed-batch fermentation with medium exchange was used to optimize the cell growth and production of ectoines by Halomonas boliviensis. A mathematical method was applied to determine the optimal conditions for biomass and ectoine production. A two-fed-batch process was then applied for obtaining high cell mass as a first step, and transferring the cells to a second fed-batch reactor with fresh medium at higher salinity to initiate ectoines synthesis. This strategy resulted in high ectoines content of 27.8 wt% and an overall ectoines volumetric productivity of 10 g L−1 d−1. Ectoines were then released from the cells by “bacterial milking” process by subjecting the cells to osmotic downshock without significant loss of cell viability. Further recultivation of the cells allowed them to re-synthesize the ectoine in a new cycle in shorter time. This resulted in an overall volumetric productivity of 11.1 g L−1 d−1, the highest reported so far for fed-batch cultivation for the production of ectoines. A process for simultaneous co-production of ectoines and PHB by H. boliviensis using two-step fed-batch cultivations with medium exchange was developed in order to reduce the production cost of both products. After obtaining high cell-density under optimum growth conditions in fed-batch cultivation, sodium chloride concentration was increased to induce ectoine synthesis, as well as limitation of nutrients was applied to achieve PHB accumulation during the second cultivation step. The result was ectoine content and volumetric productivity of 7.2 wt % and 2.8 g L−1 d−1, respectively, and the PHB content and productivity of 68.5 wt% and 1.06 g L−1 h−1, which was slightly reduced as compared to the processes where production of ectoines and the biopolymer were studied separately.
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| 4. |
- Quillaguaman, Jorge, et al.
(författare)
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Synthesis and production of polyhydroxyalkanoates by halophiles: current potential and future prospects
- 2010
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 85:6, s. 1687-1696
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Forskningsöversikt (refereegranskat)abstract
- Biodegradable materials with plastic or elastomeric properties are in great demand for a variety of applications. Polyhydroxyalkanoates (PHAs), polyesters synthesized by microorganisms, possess such desired features. Industrial production of PHAs is currently achieved using recombinant Escherichia coli. Nevertheless, recent research on halophiles, salt requiring microorganisms, has shown a remarkable potential for biotechnological production of PHAs. The halophilic archaeon Haloferax mediterranei accumulates a co-polymer, i.e., poly(3-hydroxybutyrate-co-3-hydroxyvalerate) in large amounts using glucose, starch, and hydrolyzed whey as carbon sources. Chemical composition and molecular weight of PHAs produced by H. mediterranei can be modified depending on the substrate utilized as precursor. Phylogenetic studies on haloarchaeal enzymes able to polymerize the components of PHAs (i.e., PHA synthases) reveal a novel cluster, with a close relationship with PHA polymerases of bacteria and archaea found in marine-related niches. On the other hand, sequences of PHA synthases of two halophilic bacteria are more closely affiliated to synthases of Proteobacteria. Several bacterial species of the family Halomonadaceae accumulate PHAs. Halomonas boliviensis reached PHA yields and volumetric productivities close to the highest reported so far. Furthermore, H. boliviensis and other Halomonas species are able to co-produce PHA and osmolytes, i.e., ectoines and hydroxyectoine, in one process.
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