| 1. |
- Axelsson, Jan Peter, et al.
(author)
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A Probing Approach for Detection of Acetate Formation
- 1998
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Conference paper (peer-reviewed)abstract
- Many pharmaceuticals are today produced using genetically modified microorganisms. A typical problem in monitoring and control of biotechnical processes is that many important process variables cannot be measured on-line. This has triggered much research and development concerning new sensors. Another way of addressing the problem is to improve and to extend the use of existing sensors.
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| 2. |
- Axelsson, Jan Peter, et al.
(author)
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A Probing Feeding Strategy for E. coli Cultivations
- 1999
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In: Abstract book of 217th ACS National Meeting.
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Conference paper (peer-reviewed)abstract
- Accumulation of acetate tends to reduce growth and recombinant protein production in E. coli cultivations. Formation of acetate can be avoided by a proper substrate feeding strategy, but most strategies require considerable process knowledge to work well. A feedback strategy is presented that requires minimal a priori information. The key idea is to exploit a characteristic change in the cell metabolism at the onset of acetate formation. By superimposing short pulses in the substrate feed rate, on-line detection of acetate formation can be made using a standard dissolved oxygen sensor. A simple feedback algorithm is then used to adjust the feed rate to avoid acetate formation while maintaining a high growth rate. The strategy was used in fed-batch cultivations of recombinant E. coli. Acetate accumulation was avoided and a good production of recombinant protein could be achieved at the first attempt for each genetic construction.
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| 3. |
- Axelsson, Jan Peter, et al.
(author)
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A Probing Feeding Strategy for Escherichia coli Cultures
- 1999
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In: Biotechnology Techniques. - 0951-208X. ; 13, s. 523-528
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Journal article (peer-reviewed)abstract
- A strain-independent feeding strategy for fed-batch cultures of Escherichia coli is presented. The key idea is to exploit a characteristic change in the cell metabolism at the onset of acetate formation. By superimposing short pulses in the glucose feed rate, on-line detection of acetate formation can be made using a standard dissolved oxygen sensor. A simple feedback algorithm is then used to adjust the feed rate to avoid acetate formation. The feasibility of the strategy is demonstrated by both simulation and experiments.
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| 4. |
- Axelsson, Jan Peter, et al.
(author)
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A Probing Feeding Strategy for Recombinant E. coli Cultivations
- 1999
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Conference paper (peer-reviewed)abstract
- *Summary: The bacterium Escherichia coli is a common host organism for recombinant protein production. A problem encountered is the accumulation of the by-product acetate, which tends to reduce growth and protein production (1). Formation of acetate can be avoided by a proper substrate feeding strategy, but most strategies require considerable process knowledge to work well. The main problem is that many important process variables cannot be measured on-line. This paper presents a feedback strategy for substrate feeding that is based on standard measurements and that only requires a minimum of process knowledge. The validity of the approach is demonstrated by both simulations and experiments. *Materials and Methods: Fed-batch cultivations of E. coli BL21(DE3) with different plasmids was made in a 3 L bioreactor using a defined medium. The temperature was 37 C and pH was kept at 7.0 by titration of ammonia. DO was kept around 30% saturation by manipulation of the stirrer speed. Expression of recombinant protein was initiated by addition of IPTG. OD was measured at 620 nm. Glucose and acetate concentration was determined using enzymatic kits. *Overview and discussion of results: The key idea of the novel feedback strategy is to exploit a characteristic change in the cell metabolism at the onset of acetate formation. By superimposing short pulses in the substrate feed rate, on-line detection of acetate formation can be made using a standard dissolved oxygen sensor (2). A simple feedback algorithm is then used to adjust the feed rate to avoid acetate formation while maintaining a high cell growth rate. The feasibility of the feeding strategy is demonstrated by simulations and tuning rules that require a minimum of process specific information are derived. The strategy was used in fed-batch cultivations of recombinant E. coli. Acetate accumulation was avoided and a good production of the recombinant protein was achieved. *Conclusions: A feedback strategy for substrate feeding in E. coli cultivations has been developed. An attractive feature is that only a minimum of process specific knowledge is required which makes it a valuable tool for cutting the development time for new processes. *References: (1) Bauer et al (1990) Appl. Env. Microbiol. 56, 1296-1302 (2) Akesson (1998) Licentiate Thesis ISRN LUTFD2/TFRT--3220--SE, Dept. of Automatic Control, Lund Inst. of Technology, Lund, Sweden
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| 5. |
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| 6. |
- Axelsson, Jan Peter, et al.
(author)
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A Pulse Technique for Control of Fed-batch Fermentations
- 1997
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Conference paper (peer-reviewed)abstract
- A strategy for control of substrate feed rate in fed-batch fermentations is presented. The main idea is to make pulses in the feed rate and to evaluate the response in the dissolved oxygen signal. This gives an indirect measurement of the substrate demand that is used for feedback control of the feed rate. Experimental data is used to develop a model of a fermentation process. The model is used to derive simple tuning rules that require little process specific information. Several simulation experiments show the feasibility of the presented strategy.
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| 8. |
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| 9. |
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| 10. |
- Björck-Åkesson, Eva, et al.
(author)
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Family involvement in assessment and intervention : Preceptions of professionals and parents in Sweden
- 1995
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In: Exceptional children. - 0014-4029 .- 2163-5560. ; 61:6, s. 520-535
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Journal article (peer-reviewed)abstract
- Describes perceptions of professionals and parents of the current and ideal state of family involvement in the habilitation process for children with disabilities in early intervention in Sweden. Significant discrepancies between current and ideal practices in four dimensions; Professionals' preferences for a higher degree of family involvement.
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