| 11. |
- Jarmander, Johan, 1983-
(författare)
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Improved detection and performance of surface expression from the AIDA-I autotransporter
- 2013
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Surface expression of recombinant proteins has attracted a lot of attention due to its potential in applications such as enzyme production, vaccine delivery and bioremediation. Autotransporters have been used for surface expression of a variety of proteins, but the expression systems reported in literature have typically been inflexible and incapable of detecting proteolysis, thereby limiting surface expression yield.In this thesis, a modular surface expression system, utilizing dual tag detection, was therefore created. It was based on the adhesin involved in diffuse adherence (AIDA-I) autotransporter, and was here used to express the model proteins SefA and H:gm on the cell surface of Escherichia coli. Due to the dual tag detection system, proteolysed H:gm could be successfully verified on the cell surface. By optimizing cultivation conditions, surface expression yield of SefA was increased by 300 %, and proteolysis reduced by 33 %. While proteolysis could not be eliminated completely, the work presented in this thesis is a major step towards a general system for surface expression of a wide range of proteins in varied applications.
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| 12. |
- Jaros, Adam, et al.
(författare)
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Effect of acetate on fermentation production of butyrate
- 2012
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Ingår i: Cellulose Chemistry and Technology. - 0576-9787. ; 46:5-6, s. 341-347
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Tidskriftsartikel (refereegranskat)abstract
- A carbon source for the fermentation production of butyrate is xylose extracted from ligno-cellulosic material by hot water extraction. Although this auto-hydrolysis of hemicellulose can provide a low-cost source of xylose, the process generates a high level of acetic acid that might inhibit subsequent fermentations. This study focuses on the effects of acetate on the production of butyrate from xylose by batch fermentations with a selected strain Clostridium tyrobutyricum.At initial acetate concentrations of 17.6 g L-1 and 26.3 g L-1 in the media, C. tyrobutyricum cultures exhibited a lag phase (45 and 118 hours, respectively) in terms of sugar consumption, butyrate production and cell biomass growth, lowering the overall production rate. Butyrate fermentations performed with high concentrations of acetate in the media demonstrated a re-uptake of acetate into the butyrate production pathway and after the lag phase, all cultures adapted to the inhibitory acetate, which increased the final butyrate yields by 12.6% (32.6 g L-1 compared to 28.5 g L-1).
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| 13. |
- Jaros, Adam Marschall, et al.
(författare)
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Acetate adaptation of clostridia tyrobutyricum for improved fermentation production of butyrate
- 2013
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Ingår i: SpringerPlus. - : Springer Science and Business Media LLC. - 2193-1801. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- Clostridium tyrobutyricum ATCC 25755 is an acidogenic bacterium capable of utilizing xylose for the fermentation production of butyrate. Hot water extraction of hardwood lingocellulose is an efficient method of producing xylose where autohydrolysis of xylan is catalysed by acetate originating from acetyl groups present in hemicellulose. The presence of acetic acid in the hydrolysate might have a severe impact on the subsequent fermentations. In this study the fermentation kinetics of C. tyrobutyricum cultures after being classically adapted for growth at 26.3 g/L acetate equivalents were studied. Analysis of xylose batch fermentations found that even in the presence of high levels of acetate, acetate adapted strains had similar fermentation kinetics as the parental strain cultivated without acetate. The parental strain exposed to acetate at inhibitory conditions demonstrated a pronounced lag phase (over 100 hours) in growth and butyrate production as compared to the adapted strain (25 hour lag) or non-inhibited controls (0 lag). Additional insight into the metabolic pathway of xylose consumption was gained by determining the specific activity of the acetate kinase (AK) enzyme in adapted versus control batches. AK activity was reduced by 63% in the presence of inhibitory levels of acetate, whether or not the culture had been adapted.
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| 14. |
- Matsakas, Leonidas, et al.
(författare)
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Evaluation of dried sweet sorghum stalks as raw material for methane production
- 2014
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Ingår i: BioMed Research International. - : Hindawi Limited. - 2314-6133 .- 2314-6141. ; 2014
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Tidskriftsartikel (refereegranskat)abstract
- The potential of utilizing dried sweet sorghum stalks as raw material for anaerobic digestion has been evaluated. Two different treatments were tested, a mild thermal and an enzymatic, alone or in combination. Thermal pretreatment was found to decrease the methane yields, whereas one-step enzymatic treatment resulted in a significant increase of 15.1% comparing to the untreated sweet sorghum. Subsequently, in order to increase the total methane production, the combined effect of enzyme load and I/S on methane yields from sweet sorghum was evaluated by employing response surface methodology. The obtained model showed that the maximum methane yield that could be achieved is 296 mL CH4/g VS at I/S ratio of 0.35 with the addition of 11.12 FPU/g sweet sorghum.
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| 15. |
- Matsakas, Leonidas, et al.
(författare)
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Use of dried sweet sorghum for the efficient production of lipids by the yeast Lipomyces starkeyi CBS 1807
- 2014
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Ingår i: Industrial crops and products (Print). - : Elsevier BV. - 0926-6690 .- 1872-633X. ; 62, s. 367-372
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Tidskriftsartikel (refereegranskat)abstract
- The ability of the oleaginous yeast Lipomyces starkeyi to efficiently produce lipids when cultivated on saccharified sweet sorghum stalks juice was evaluated. Initially the production of lipids using synthetic media mimicking sweet sorghum stalks has been studied and optimized concerning the nitrogen source and the C:N ratio. Under optimum conditions (yeast extract as nitrogen source and C:N ratio of 190) the lipid production reached 5.81 g/L with a lipid content of 47.3% (w/w) from a mixture of sucrose, glucose and fructose, mimicking the sugar composition of sorghum. When cultivated on sweet sorghum stalks juice, it was observed that no external nitrogen addition was necessary which could result in substantial decrease of the initial C:N ratio. Moreover a distinct saccharification process prior to yeast cultivation improved the lipid production yield as it resulted in an increase of the C:N ratio. The highest lipid production, which was 6.40 g/L with a lipid content of 29.5% (w/w), was obtained when juice from saccharified sweet sorghum stalks at an initial sorghum content of 12% (w/w) was used as feedstock.
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| 16. |
- Mesfun, Sennai, et al.
(författare)
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Black liquor fractionation for biofuels production : A techno-economic assessment
- 2014
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 166, s. 508-517
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Tidskriftsartikel (refereegranskat)abstract
- The hemicelluloses fraction of black liquor is an underutilized resource in many chemical pulp mills. It is possible to extract and separate the lignin and hemicelluloses from the black liquor and use the hemicelluloses for biochemical conversion into biofuels and chemicals. Precipitation of the lignin from the black liquor would consequently decrease the thermal load on the recovery boiler, which is often referred to as a bottleneck for increased pulp production. The objective of this work is to techno-economically evaluate the production of sodium-free lignin as a solid fuel and butanol to be used as fossil gasoline replacement by fractionating black liquor. The hydrolysis and fermentation processes are modeled in Aspen Plus to analyze energy and material balances as well as to evaluate the plant economics. A mathematical model of an existing pulp and paper mill is used to analyze the effects on the energy performance of the mill subprocesses.
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| 17. |
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| 18. |
- Nilsson, Robert, et al.
(författare)
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Techno-economics of carbon preserving butanol production using a combined fermentative and catalytic approach
- 2014
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Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524 .- 1873-2976. ; 161, s. 263-269
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a novel process for n-butanol production which combines a fermentation consuming carbon dioxide (succinic acid fermentation) with subsequent catalytic reduction steps to add hydrogen to form butanol. Process simulations in Aspen Plus have been the basis for the techno-economic analyses performed. The overall economy for the novel process cannot be justified, as production of succinic acid by fermentation is too costly. Though, succinic acid price is expected to drop drastically in a near future. By fully integrating the succinic acid fermentation with the catalytic conversion the need for costly recovery operations could be reduced. The hybrid process would need 22% less raw material than the butanol fermentation at a succinic acid fermentation yield of 0.7 g/g substrate. Additionally, a carbon dioxide fixation of up to 13 ktonnes could be achieved at a plant with an annual butanol production of 10 ktonnes
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| 19. |
- Sjöblom, Magnus, et al.
(författare)
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Secretion and expression dynamics of a GFP-tagged mucin-type fusion protein in high cell density Pichia pastoris bioreactor cultivations
- 2012
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Ingår i: Advances in Bioscience and Biotechnology. - : Scientific Research Publishing, Inc.. - 2156-8456 .- 2156-8502. ; 3:3, s. 238-248
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Tidskriftsartikel (refereegranskat)abstract
- The methanol inducible alcohol oxidase 1 promoter and the Saccharomyces cerevisiae alpha-factor prepro secretion signal were used to drive expression and secretion of a mucin-type fusion protein by Pichia pastoris in 1 L scale bioreactors. The aim of the study was to understand how varying expression rates influenced the secretion dynamics of the fusion protein in terms of intracellular- and extracellular concentrations. Endoplasmic reticulum (ER) folding stress was assessed by the relative expression of the unfolded protein response controlled KAR2 gene. Three predefined methanol feeding models were applied to control the fusion protein synthesis rate. To track the fusion protein synthesis in a non-invasive manner and to follow its intracellular distribution, its C-terminal was linked to the green fluorescent protein. Under all conditions the fusion protein was found to partially accumulate intracellularly, where the major fraction was an insoluble, fluorescent full-sized protein. The high degree of glycosylation of the insoluble fusion protein indicated a secretory bottle-neck in the Golgi-system. This result was consistent with low ER folding stress as quantified by the relative expression of the KAR2 gene. Reduction of recombinant protein synthesis rate, by using lower feed rates of methanol, enhanced extracellular concentrations from 8 to 18 mg·L–1 and reduced the rate of intracellular accumulation. This clearly demonstrates the importance of tuning the synthesis rate with secretory bottle-necks to maintain secretion.
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