| 1. |
- de Maré, Lena, et al.
(författare)
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A cultivation technique for E. coli fed-batch cultivations operating close to the maximum oxygen transfer capacity of the reactor
- 2005
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Ingår i: Biotechnology Letters. - : Springer Science and Business Media LLC. - 0141-5492 .- 1573-6776. ; 27:14, s. 983-990
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Tidskriftsartikel (refereegranskat)abstract
- A cultivation strategy combining the advantages of temperature-limited fed-batch and probing feeding control is presented. The technique was evaluated in fed-batch cultivations with E. coli BL21(DE3) producing xylanase in a 3 liter bioreactor. A 20% increase in cell mass was achieved and the usual decrease in specific enzyme activity normally observed during the late production phase was diminished with the new technique. The method was further tested by growing E. coli W3110 in a larger bioreactor (50 l). It is a suitable cultivation technique when the O2 transfer capacity of the reactor is reached and it is desired to continue to produce the recombinant protein.
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| 2. |
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| 3. |
- Malinovskiy, Dmitry, et al.
(författare)
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Determination of the isotopic composition of molybdenum in the bottom sediments of freshwater basins
- 2007
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Ingår i: Geochemistry International. - 0016-7029 .- 1556-1968. ; 45:4, s. 381-389
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents the results of measurements of the Mo isotopic composition in the bottom sediments (BS) of freshwater basins. Mo isotopic ratios were measured using a multicollector inductively coupled plasma mass spectrometer (MC ICP MS). Efficient methods were used in this study for Mo separation from the elements of the sample matrix and correction for instrumental mass discrimination. This allowed us to achieve a high accuracy of 0.06, 0.08, and 0.14‰ (2 σ) for the measurement of 97Mo/95Mo, 98Mo/95Mo, and 100Mo/95Mo, respectively. The range of variations in Mo isotope ratios observed in the collected BS columns was ∼2.2‰ in terms of δ97Mo/95Mo. The results obtained here suggest that geochemical processes occurring during Mo migration with land water can change the isotopic composition of Mo. It is pointed out that the potential use of Mo isotopic systematics for reconstructions of redox conditions in seawater over the geologic past requires the quantification of isotopic effects of Mo accompanying its migration on land and the extent of possible variations in the isotopic composition of Mo entering the ocean.
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| 4. |
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| 5. |
- Enman, Josefine, et al.
(författare)
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Raman analysis of synthetic eritadenine
- 2008
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Ingår i: Journal of Raman Spectroscopy. - : Wiley. - 0377-0486 .- 1097-4555. ; 39:10, s. 1464-1468
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Tidskriftsartikel (refereegranskat)abstract
- Eritadenine, 2(R),3(R)-dihydroxy-4-(9-adenyl)-butyric acid, is a cholesterol-reducing compound naturally occurring in the shitake mushroom (Lentinus edodes). To identify the unknown Raman spectrum of this compound, pure synthetic eritadenine was examined and the vibrational modes were assigned by following the synthesis pathway. This was accomplished by comparing the known spectra of the starting compounds adenine and D-ribose with the spectra of a synthesis intermediate, methyl 5-(6-Aminopurin-9H-9-yl)-2,3-O-isopropylidene-5-deoxy-β-D-ribofuranoside (MAIR) and eritadenine. In the Raman spectrum of eritadenine, a distinctive vibrational mode at 773 cm-1 was detected and ascribed to vibrations in the carbon chain, ν(C--C). A Raman line that arose at 1212 cm-1, both in the Raman spectrum of MAIR and eritadenine, was also assigned to ν(C--C). Additional Raman lines detected at 1526 and at 1583 cm-1 in the Raman spectrum of MAIR and eritadenine were assigned to ν(N--C) and a deformation of the purine ring structure. In these cases the vibrational modes are due to the linkage between adenine and the ribofuranoside moiety for MAIR, and between adenine and the carbon chain for eritadenine. This link is also the cause for the disappearance of adenine specific Raman lines in the spectrum of both MAIR and eritadenine. Several vibrations observed in the spectrum of D-ribose were not observed in the Raman spectrum of eritadenine due to the absence of the ribose ring structure. In the Raman spectrum of MAIR some of the D-ribose specific Raman lines disappeared due to the introduction of methyl and isopropylidene moieties to the ribose unit. With the approach presented in this study the so far unknown Raman spectrum of eritadenine could be successfully identified and is presented here for the first time.
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| 6. |
- Andersson, Christian
(författare)
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Biobased production of succinic acid by Escherichia coli fermentation
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The prospects of peak oil, climate change and the dependency of fossil carbon have urged research and development of production methods for the manufacture of fuels and chemicals from renewable resources (biomass). The present thesis illustrates different aspects of biobased succinic acid production by a metabolically engineered E. coli strain. The main areas of the thesis are sugar utilisation and feedstock flexibility, and fermentation inhibition, both due to toxic compound derived from the raw material and the fermentation products themselves.The first part of this thesis aimed to investigate the fermentation characteristics of AFP184 in a medium consisting of corn steep liquor, inorganic salts and different sugar sources without supplementation with high-cost nutrients such as yeast extract and peptone. The effects of different sugars, sucrose, glucose, fructose, xylose, equal mixtures of glucose-fructose and glucose-xylose, on succinic acid production kinetics and yields in an industrially relevant medium were investigated. AFP184 was able to utilise all sugars and sugar combinations except sucrose for biomass generation and succinate production. Using glucose resulted in the highest yield, 0.83 (g succinic acid per g sugar consumed anaerobically). Using a high initial sugar concentration resulted in volumetric productivities of almost 3 g L-1 h-1, which is above estimated values for economically feasible production. However, succinic acid production ceased at final concentrations greater than 40 g L-1. To further increase succinic acid concentrations, fermentations using NH4OH, NaOH, KOH, K2CO3, and Na2CO3 as neutralising agents were performed and compared. It was shown that substantial improvements could be made by using alkali bases to neutralise the fermentations. The highest concentrations and productivities were achieved when Na2CO3 was used, 77 g L-1 and 3 g L-1 h-1 respectively. A gradual decrease in succinate productivity was observed during the fermentations, which was shown to be due to succinate accumulation in the broth and not as a result of the addition of neutralising agent or the subsequent increase in osmolarity.To maintain high succinate productivity by keeping a low extracellular succinic acid concentration fermentations were interrupted and cells recovered and resuspended in fresh media. By removing the succinate it was possible to maintain high succinic acid productivity for a prolonged time. Cells subjected to high concentrations of succinate were also able to regain high productivity once transferred into a succinate-free medium.In the last part of the thesis succinic acid production from softwood dilute acid hydrolysates was demonstrated. This study involved establishing the degree of detoxification necessary for growth and fermentation using industrial hydrolysates. Detoxification by treatment with lime and/or activated carbon was investigated and the results show that it was possible to produce succinate from softwood hydrolysates in yields comparable to those for synthetic sugars.The work done in this thesis increases the understanding of succinic acid production with AFP184, illustrate its limitations, and suggests improvements in the current technology with the long term aim of increasing the economical feasibility of biochemical succinic acid production.
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| 7. |
- Andersson, Christian, et al.
(författare)
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Effect of different carbon sources on the production of succinic acid using metabolically engineered Escherichia coli
- 2007
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Ingår i: Biotechnology progress (Print). - : Wiley. - 8756-7938 .- 1520-6033. ; 23:2, s. 381-388
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Tidskriftsartikel (refereegranskat)abstract
- Succinic acid (SA) is an important platform molecule in the synthesis of a number of commodity and specialty chemicals. In the present work, dual-phase batch fermentations with the E. coli strain AFP184 were performed using a medium suited for large-scale industrial production of SA. The ability of the strain to ferment different sugars was investigated. The sugars studied were sucrose, glucose, fructose, xylose, and equal mixtures of glucose and fructose and glucose and xylose at a total initial sugar concentration of 100 g L-1. AFP184 was able to utilize all sugars and sugar combinations except sucrose for biomass generation and succinate production. For sucrose as a substrate no succinic acid was produced and none of the sucrose was metabolized. The succinic acid yield from glucose (0.83 g succinic acid per gram glucose consumed anaerobically) was higher than the yield from fructose (0.66 g g-1). When using xylose as a carbon source, a yield of 0.50 g g-1 was obtained. In the mixed-sugar fermentations no catabolite repression was detected. Mixtures of glucose and xylose resulted in higher yields (0.60 g g-1) than use of xylose alone. Fermenting glucose mixed with fructose gave a lower yield (0.58 g g-1) than fructose used as the sole carbon source. The reason is an increased pyruvate production. The pyruvate concentration decreased later in the fermentation. Final succinic acid concentrations were in the range of 25-40 g L-1. Acetic and pyruvic acid were the only other products detected and accumulated to concentrations of 2.7-6.7 and 0-2.7 g L-1. Production of succinic acid decreased when organic acid concentrations reached approximately 30 g L-1. This study demonstrates that E. coli strain AFP184 is able to produce succinic acid in a low cost medium from a variety of sugars with only small amounts of byproducts formed.
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| 8. |
- Andersson, Christian, et al.
(författare)
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Effects of neutralising agent, organic acids, and osmolarity on succinic acid production by Escherichia coli AFP184
- 2008
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Using a low-cost medium Escherichia coli AFP184 has previously been reported to produce succinic acid with volumetric productivities close to 3 g L-1 h-1. At a total organic acid concentration of 30 g L-1 the productivity decreased drastically resulting in final succinate concentrations of 40 g L-1. The economical viability of biochemical succinic acid production would benefit from higher final succinic acid concentrations and volumetric productivities maintained at >2.5 g L-1 h-1 for an extended period of time. In the present work the effects of osmolarity and neutralising agent (NH4OH, KOH, NaOH, K2CO3, and Na2CO3) on succinic acid production by AFP184 were investigated. Highest concentration of succinic acid was obtained with Na2CO3, 75 g L-1. It was also found that the osmolarity resulting from succinate production and subsequent base addition, only marginally affected the productivity per viable cell. Organic acid inhibition due to the produced succinic acid on the other hand significantly reduced succinic acid productivity per viable cell. When using NH4OH productivity completely ceased at approximately 40 g L-1. Volumetric productivities remained at 2.5 g L-1 h-1 for 5 to 10 hours longer when using K- or Na-bases than when using NH4OH. However, loss of cell viability occurred, and together with the acid inhibition decreased the volumetric productivities. In this study it was demonstrated that by altering the neutralising agent it was possible to increase the period of high volumetric productivity in the anaerobic phase and improve the final succinic acid concentration by almost 100 %
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| 9. |
- Andersson, Christian, et al.
(författare)
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Inhibition of succinic acid production in metabolically engineered Escherichia Coli by neutralizing agent, organic acids, and osmolarity
- 2009
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Ingår i: Biotechnology progress (Print). - : Wiley. - 8756-7938 .- 1520-6033. ; 25:1, s. 116-123
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Tidskriftsartikel (refereegranskat)abstract
- The economical viability of biochemical succinic acid production is a result of many processing parameters including final succinic acid concentration, recovery of succinate, and the volumetric productivity. Maintaining volumetric productivities >2.5 g L-1 h(-1) is important if production of succinic acid from. renewable resources should be competitive. In this work, the effects of organic acids, osmolarity, and neutralizing agent (NH4OH, KOH, NaOH, K2CO3, and Na2CO3) on the fermentative succinic acid production by Escherichia coli AFP184 were investigated. The highest concentration of succinic acid, 77 g L-1. was obtained with Na2O3. In general, irrespective of the base used, succinic acid productivity per viable cell was significantly reduced as the concentration of the produced acid increased. Increased osmolarity resulting from base addition during succinate production only marginally affected the productivity per viable cell. Addition of the osmoprotectant glycine betaine to cultures resulted in an increased aerobic growth rate and anaerobic glucose consumption rate, but decreased succinic acid yield. When using NH4OH productivity completely ceased at a succinic acid concentration of similar to 40 g L-1. Volumetric productivities remained at 2.5 g L-1 h(-1) for tip to 10 h longer when K- or Na-bases where used instead of NH4OH. The decrease in cellular succinic acid productivity observed during the anaerobic phase was found to be due to increased organic acid concentrations rather than medium osmolarity.
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| 10. |
- Andersson, Christian, et al.
(författare)
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Process for producing succinic acid from sucrose
- 2005
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Patent (populärvet., debatt m.m.)abstract
- A process for hydrolyzing sucrose to glucose and fructose using succinic acid is described. The hydrolysate can be used to produce purified glucose and/or fructose or can be used as a carbon source for fermentations to produce various chemicals including succinic acid.
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