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4. increased enzyme production was achieved in the airlift bioreactor compared to the stirred-tank bioreactor. Higher glucoamylase productivity (70 %) was obtained in batch cultures. in continuous suspension culture, it was also show that the enzyme production decreased more rapidly in the stined-tank bioreactor because plasmid loss was faster than in the airW bioreactor. This was possibly due to the vigorous fluid movement and wide variation of shear forces caused by agitation. Airüft bioreacton provide more uniform h ydmdynarnic and mas transfer c haracteristics. Double selection pressure was used to select and maintah the recombinant strain. The selected strain showed better production performance than the original suah in both airlift and stured-tank bioreactors. 5. Based on this work and the iitenture, a semi-senrctwed metabolic model was developed for describing ceii growth. subsuate consumption. ethanol formation and utilization, plasmid loss and recombinant protein production of recombinant yeast By combining the Monod equation and segregational instabüity kinetics with the key chmcteristics in yeast metabolism, the proposed model has feamres of simpiicity and accuncy. The proposed model simulated the Crabtree effect. diamic growth, plasmid los and recombinant protein production. The model contains 18 parameters which cm be estimated fmm either experimentaI data or iiterature idormation. Most of the parameters are generd and suitable for different yeast recombinant saains. When the model was applied to the barch and continuous fermentations of the present recombinant yeast (C468/pGAC9), excellent agreement between mode1 predictions and experimentai results was achieved for giucose, ceil mas, ethanol, glucoamylase and fraction of plasmid-bearing
cells. Tests of the proposed model were also carried out with pubüshed experimental data fmm independent researchers. The model successfuUy predicted the experimental data for different recombinant yeast strains The sirnplicity, feasibility, accuracy and generality of the model rnake it very usefi11 for designing, scaiing-up, controlling and optimizing recombinant yeast fermentation processes. 6. An immobilized-cell-fi airlift bioreactor was developed for the recombinant yeast. The performance of the UNnobilized ceU system was compared with the corresponding free suspension ce11 system at different dilution ntes using the YPG nonselective medium. Enhanced enzyme pmductivity and production stability in the immobilized cell system were observed. Expenmental data indicated that the immobilized cells maintained a higher proportion of plasmid-bearing cells for longer penods under continuous opention. By opentinp the immobilized-celi-film bioreactor in repeated batch mode. the stability of the recombinant yeast was funher improved. ïhis is possibly the result of retention of a higher proponion of plasmici-karing cells in the immobilizûtion mauix. The attached yeast fürn behaved as a plasmid-bearing c d reservoir and continuously generated plasmid- bearing cells. providing for enhanced apparent plasmid stability. 7. A mathematical model was developed to describe plasmid loss and enzyme production Jecay kinetics in the bobilized recombinant yeast system based on ûn ideaiized biofilm model. Correlation between plasmid loss and enzyme production decay was estabüshed. The pmposed model successfully described the enhanced effects observed in the
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BIOREACTOR STUDIES OF HETEROLOGOUS
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nie University of Waterloo requin%
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ate depended on activities of the p
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Acknowiedgments Fmt of aü, 1 am ve
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2.6. Concluding Rernarks ..........
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5.3.3. Simlilated Results for Prese
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Table 1.1. Table 1.2. Table 1.3. Ta
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Figure 2.1. Figure 3.1. Figure 3.2.
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during Continuous Culture in Airlif
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Figure 5.3. Comparison between Mode
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Cell Systern at Glucose Feed Concen
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a .......... growth ratio (dimensio
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Y, ... ethanol yield for fermentati
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foreign plasmids. One major chalien
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than the denanired, inclusion body
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Table 1.2. Strategies for Enhancing
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Table 1.3. Host Cek, Pfasmids, Gene
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1.4. Immo bilized-Cell Bioreactors
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1. Study the gmwth characteristics,
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plasmid are used; or chromaromal DN
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2.2.1. Genetic Factors 2.2.1.1. Pid
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1- fkquently than a plasmid with Io
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Da Silva and Bailey (1991) used the
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LEU2 or TRPI is cloned into the aux
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eported reduced stabiliity in the s
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on metabolic pathways. In the ferme
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OC), oniy about 35% of the populati
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loss @) is dehned as the probabilit
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+ s Dilution Rate = p' = CI,- - K*+
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concentration couid Iead to coexist
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that factors other than immobiiizat
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earing and plasmid-tke =Ils. Gel be
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productivity irrespective of the mo
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inactive and useless. The problern
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Aerobic fermentation osing iamnobih
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(ranghg h m 1 to 7) on citric acid
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celi fraction decreases monotonicai
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(1987) model aliows for plasmid ins
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affect plasmid stability have ben o
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CEtAPTER 3 MATERIALS AND METHODS 3.
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stiU deleted hm the plasmid. Such p
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1) Reagent solution preparation was
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nonse1ective agar plates, but only
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working Liquid volume. The aeration
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3.5. UNnobilized Ceil Culture 35.1.
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3.52 Cd Lmmobiiization Yeast attach
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3.6. Experimental Error and Reprodu
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-0-Cell(1) +Total CeII (2) 4- Ethan
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* . I I a O 2 4 6 8 10 12 14 Batche
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Cell Maso, Glucose and EthanoI(g1L)
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4.2.2. Batch CuIture in Stirreà-Ta
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[t ~lucoamylase (ALR) -e Glucoamyla
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The finai giucoamyiase concentratio
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Bentley and Kompala, 1989; Satyagal
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160 First ExponenUaI Phase 1 -c ALR
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Figure 4hl. Pathways of Yeast Intem
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fermentation (using nitrogen spargi
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43. Continuous Suspension Culture C
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Figure 4.9. Continuous Suspension C
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1 +Enzyme +Fradlan of PBC +CeIl Mas
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Figures 4.12 and 4.13 show that by
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Fi- 4.13. Cornparison of Glu~iase C
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where 6 = p- - p' + pp*, which is a
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Figure 4-14. Effeds of Dilution Rat
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Impoolsup et ai. (1989a) and Hardji
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Figure 4.16. dB/dt versus B Plots a
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Figure 4.17. Totai Cell Mas at Diff
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another recombinant yeast (impoolsu
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other recombinant yeast under nonse
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4.3.4. Effixt of Dilution Rate On R
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Figure 4.18- Etlects of Mluiioa Rat
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Number of Generations - - - - - - *
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B Table 4.5. Metabolic Pathway Anal
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concentration. But this may be more
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[+ Enzyme (ALR) + Enzyme (STR) +Fra
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necessary for host ce& to grow in t
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Glucoamylase ConcentraUon (unltsll)
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[a Selective Medium A Nonseiective
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5.1 Introduction CHAPTER 5 MODELING
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handle. excess glucose is femented
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The carbon fluxes h m the three met
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53. Modei Simulation in Batch CuItu
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Table 5.1. Summary of Parameters fo
Page 167 and 168: 1 n Glucose o Cell Mass O Ethano1 A
Page 169 and 170: detennined in the cunent study, the
Page 171 and 172: Figure 5.4. Cornparison between Mod
Page 173 and 174: equations are üsted in Appendix G.
Page 175 and 176: a dilution rate at which the giucoa
Page 177 and 178: [ o Expetfmental data -Simuiated mt
Page 179 and 180: The effixts of dilution rate on the
Page 181 and 182: Ttme (hrs) 1 a Enzyme A Phsrnid-Bea
Page 183 and 184: It may take several generations for
Page 185 and 186: understanding of the nature of the
Page 187 and 188: On the other hand. the net accumula
Page 189 and 190: Differentiating Equation (6.20) res
Page 191 and 192: Enyme collcentration m the t>ioreac
Page 193 and 194: Glucoamylase Concentration (units/L
Page 195 and 196: 50 100 150 200 Time (hrs) 1 O Free
Page 197 and 198: F i 6.6. Cornparison of Fnx Cd Mars
Page 199 and 200: . - O 50 100 150 200 250 nme (hrs)
Page 201 and 202: Nasi et ai.. 1988) and recombinant
Page 203 and 204: estimated by using Equation (6.24)
Page 205 and 206: [a lmmobilked System O Free System
Page 207 and 208: oxidation pathway. W~th increasing
Page 209 and 210: O 50 100 150 200 250 300 Tirne (hrs
Page 211 and 212: epeated batch fermentations, the fe
Page 213 and 214: Glucoamylase Concentration (unitslL
Page 215 and 216: 6) Suitable for repeated-batch and
Page 217: ecause glucose fermentation dominat
Page 221 and 222: 7.2. Recommendations The foUowing f
Page 223 and 224: APPENDIX A: PLASMID MAP FOR pGAC9 l
Page 225 and 226: where Bi (Biot number) = - ks De @
Page 227 and 228: APPENDK C. EFFECTS OF INITIAL GLUCO
Page 229 and 230: Figure C.2. Effect of Initial Gluco
Page 231 and 232: Figure C.4 Effect of Initial Glucos
Page 233 and 234: APPENDLX D. COMPARISON OF ORIGINAL
Page 235 and 236: (continue)
Page 237: (continue)
Page 242 and 243: E.2. Batch Fermentation with Recomb
Page 246 and 247: (continue) tfhJ 0.5 10.5 12.75 12.5
Page 250 and 251: E.3.2. Experimental Data (Parker an
Page 252 and 253: Run No: CALE (Selected Strain. D =
Page 254 and 255: Run No: CALR 5 (Original Suain, D =
Page 256 and 257: Run No: CSTR3 (Selected Suain, D =
Page 260 and 261: Run No: CICR2 (Selected Suain, D =
Page 262 and 263: Run No: CiCR4 (Selected Suain, D =
Page 264 and 265: Eh. Repeated Batch Culture in hmobi
Page 266 and 267: APPENDIX F. C CODE FOR THE PROPOSED
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* the initial data */ /* gening the
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* getting the founh term in R-K met
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I*Plasrnid-bearing ceU concentratio
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* Func tion C 1 */ îloat C l(float
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APPEMIM G. EXAMPLES OF MAPLE V CODE
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REFERENCES Ataai. MM. and Shuler. M
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Caunt, P.. hpoolsup, A.. and Greenf
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cuitanes of E. coli BZ18@TG 201) wi
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Gabrieisen. O.S. et aL (1990), Effi
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Huang, C-T., Peretti, S.W., and Bry
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Kim, B.G. and Shuler, M.L. (1990a),
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Lee, S.B.. Ryu, D.D.Y., seigel, R,
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Nasri, M., Sayadi. S.. Barbotin, J.
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Pin, S.J. and Kmwski. W.M. (1970),
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Seo, I-H. and Bailey. J.E. (1985).
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Tumer. B.G., Avgerinos G-C.? Melnic
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Yu, J. and Tang, X (Editor, 1991),
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