| 1. |
- de Maré, Lena, et al.
(author)
-
Cultivations of Vibrio cholerae using probing control of glucose feeding
- 2002
-
In: [Host publication title missing]. ; , s. 62-62
-
Conference paper (peer-reviewed)abstract
- One reason for cultvating Vibrio cholera is for production of CTB, which is a component in a cholera vaccine. Techniques of high cell density fermentation developed for recombinant E. coli are investigated.In the literature there is evidence of acetate formation when cultivating V. cholerae, and it is probable that the acetate has the same negative consequences for V. cholerae as for E. coli. Formation of acetate in E. coli cultures occurs under anaerobic conditions, but also under fully aerobic conditions in situations with excess carbon source.Mats Åkesson has developed a probing feeding strategy, which avoid overflow metabolism while maintaining a high growth rate. The probing feeding strategy consists of pulses that are superimposed to the glucose feed. The pulses give rise to changes in the glucose uptake, which can be seen in the dissolved oxygen measurements. A feedback algorithm uses the information from the pulse responses to change the feed rate. A safety net decreases the feed rate when maximal stirrer speed is reached to avoid oxygen limitations. The probing feeding has been tested in five fed - batch cultivations with V. cholerae JS1596 in defined media. The strategy is working as well for V. cholerae as for E. coli in minimizing the amount acetic acid formed and avoiding anaerobic conditions. Two hours after the feed start most of the acetic acid accumulated during the batch phase is consumed. During this acetic acid consumption period the resulting growth rate is a bit lower than later on when the acetic acid is depleted. The probing feeding strategy thus gives favorable cultivation conditions in a controlled way.
|
|
| 2. |
- de Maré, Lena, et al.
(author)
-
Probing control of glucose feeding in Vibrio cholerae cultivations
- 2003
-
In: Bioprocess and Biosystems Engineering. - : Springer Science and Business Media LLC. - 1615-7605 .- 1615-7591. ; 25:4, s. 221-228
-
Journal article (peer-reviewed)abstract
- Infection with Vibrio cholerae is a significant problem in manydeveloping countries. Cultivation of Vibrio cholerae is used inproduction of CTB, which is a component in a cholera vaccine. Fed - batch cultivations with V. cholerae in defined mediahave been conducted and reproducible results were obtained. A probing feeding strategy developed by Åkessonfor E. coli cultivations has been tested.The program is working as well for V. cholerae as forE. coliin minimizing the amount acetic acid formed and avoiding anaerobicconditions. Two hours after the feed start most of the acetic acidaccumulated during the batch phase is consumed. The resulting feedrate tends to be thehighest possible with respect to the constraints from cell metabolismand mass transfer, thus maximizing productivity in terms of biomass.A cell dry weight of 20 - 23 g/l is obtained after12 hours of feeding.
|
|
| 3. |
- de Maré, Lena, et al.
(author)
-
A cultivation technique for E. coli fed-batch cultivations operating close to the maximum oxygen transfer capacity of the reactor
- 2005
-
In: Biotechnology Letters. - : Springer Science and Business Media LLC. - 0141-5492 .- 1573-6776. ; 27:14, s. 983-990
-
Journal article (peer-reviewed)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.
|
|
| 4. |
- de Maré, Lena, et al.
(author)
-
Feedback control of flow rate from a peristaltic pump using balance measurements
- 2001
-
Conference paper (other academic/artistic)abstract
- In many biotechnological processes it is important to perform exactdosing of the substrate into the bioreactor. The idea in this paper is to use the measurements from a balance to control the flow rate, since there is no access to the flow itself. The goals of the controller are several: it should be capable of handling load disturbances acting on the pump, measurement noise and even shocks acting on the balance. For this purpose an observer disregarding outliers is designed for low influence of the measurement noise. The observer-based feedback term compensates the load disturbances and the model errors. A dynamic feed forward structure is introduced to speed up the setpoint response. Simulation experiments show that the suggested controller structure works well.
|
|
| 5. |
- de Maré, Lena
(author)
-
Feeding Strategies Based on Probing Control for E. coli and V. cholerae Cultivations
- 2006
-
Doctoral thesis (other academic/artistic)abstract
- The recombinant DNA techniques have made it possible to produce many different proteins for a wide range of applications. The vector encoding for the recombinant protein is often inserted in the bacterium E. coli as it is a well studied and a well-known organism. To achieve a high productivity, it is important to reach a high cell density. This is obtained through fed-batch operation where the nutrient, usually glucose, is added continuously. The feeding strategy should be designed to avoid starvation and overfeeding. This is not an easy task as on-line measurements of key variables are normally not available. A probing feeding strategy using the measurements of the standard dissolved oxygen sensor is developed by M. Åkesson. The key idea is to superimpose pulses on the feed-rate and make use of the responses in the dissolved oxygen in a feedback algorithm. Also, when the maximum transfer capacity of the reactor is reached the feed-rate is decreased in order to keep the reactor working under aerobic conditions. The strategy has been successfully implemented in cultivations with different E. coli strains and on different scales. The probing feeding strategy is further developed in many aspects in this thesis. Firstly, it is implemented with good results also in V. cholerae cultivations, which shows how general the strategy is. Also, a model of a bio-reactor operating in fed-batch mode is presented and verified. The effect on the tuning rules of the probing controller is investigated. The probing feeding strategy is further improved for a more efficient product synthesis. This new fermentation technique manipulates the temperature when the maximum oxygen transfer capacity of the reactor is reached. The strategy consists of a mid-ranging controller structure and a modified probing controller. It is analysed and evaluated in experiments and simulations. Furthermore, some E. coli production strains need additions of amino acids or complex media besides the carbon nutrient to grow and produce the recombinant protein. The probing control concept is therefore extended in order to handle these situations. Feeding strategies for dual feeding of amino acids or complex media and glucose are developed.
|
|
| 6. |
- de Maré, Lena, et al.
(author)
-
Feeding strategies for E-coli fermentations demanding an enriched environment
- 2007
-
In: Bioprocess and Biosystems Engineering. - : Springer Science and Business Media LLC. - 1615-7605 .- 1615-7591. ; 30:1, s. 13-25
-
Journal article (peer-reviewed)abstract
- The addition of a carbon nutrient feed to a fed-batch cultivation is often not enough to obtain satisfactory growth and/or production. In some cases, an additional feed with for example supplementary amino acids or complex media is required. This work presents the development of feeding strategies where more than one feed is required and the knowledge of the growth requirements is low. Simulations and cultivations with E. coli are shown using the proposed feed controllers which are based on a probing control concept. The strategies work well and they can be used to shorten the process development phase considerably.
|
|
| 7. |
|
|
| 8. |
- de Maré, Lena, et al.
(author)
-
Simuleringar och analys av V. Cholerae odling där feeden styrs genom återkoppling från ättiksyramätningar
- 2002
-
Reports (other academic/artistic)abstract
- På Linköpings tekniska högskola har man tillgång till många olika sätt att mäta ättiksyra i en bioreaktor. Utrustningen för att mäta ättiksyra består av en NIR (near infrared spectroscopy) som mäter online och en samplingstid på sekund nivå kan uppnås. HPLC (high-performance liquid chromatography) finns det också tillgång till. Där räknar man med att ta prover var 15 min och att själva analysen tar ca 15 min. Näsan kan också användas och där räknar man med en samplingshastighet på 15 min men med att själva analysen sedan tar någon minut. Målet med denna rapport är att undersöka genom simuleringar hur det skulle fungera att styra feeden in till reaktorn med återkoppling från ättiksyra genom mätningar på de tre ovan nämda sätten. Robusthet mot störningar och även systemets stabilitet har undersökts. Det verkar som att det går bra att använda ättiksyramätningarna för att reglera feeden. Enligt simuleringar fungerar en enkel P regulator väl i fallet med NIR om inte mätbruset är stort. I så fall krävs en PI regulator. Då HPLC eller näsan används ser det ut att räcka med en PI regulator, men troligen behövs även reglering runt en profil.
|
|
| 9. |
- de Maré, Lena, et al.
(author)
-
Temperature limited fed-batch cultivation with a probing feeding strategy for Escherichia coli
- 2004
-
In: Computer Applications in Biotechnology 2004. - 008044251X ; , s. 73-79
-
Conference paper (peer-reviewed)abstract
- A cultivation strategy combining the advantages of temperature limitedfed-batch and probing control is presented.This is a suitable way to produce recombinant proteins while minimizing therelease of endotoxins which complicates the downstream processing.The downside with the temperature limited fed-batch technique has been the difficulty to achieve a controlled excess of glucose inthe reactor without the accumulation of acetic acid when usingstandard sensors.A method using a probing feeding strategy withdown-pulses is here suggested. The technique is investigated insimulations and experiments.
|
|
| 10. |
- Petersson, Mikael, et al.
(author)
-
Implementation of a Tool for Control Structure Assessment
- 2002
-
In: Proceedings of the 15th IFAC World Congress, Barcelona, Spain. - : IFAC.
-
Conference paper (peer-reviewed)abstract
- A method for assessing disturbances in SISO loops has been developed. The method indicates if the SISO loop under consideration will benefit from an addition of feedforward control from a measured disturbance. An implementation in Java of the methodology is presented in the paper.
|
|
