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6.1. Introduction CBAPI'ER 6 IMMOBILIZED RECOMBINANT YEAST CULTURE Through the experimental nsults and modeUing discussed in Chapters 4 and 5, a better understanding of the nature of the recombinant yeast was obtained. In the foilowing sections, effects of immobilization on the behaviow of the recombinant yeast wiU be addressed. Use of immo~on as an alternative method for maintaining genetic stability under nonselective conditions has k n examined (Kwnar and Schugerl. 1990). Enhanced genetic stability and productivity of recombinant products were observed in both immobiiized recombinant E. coli and recombinant S. cerevisiae. However, a general explanation for the enhancement û stül lacking. In this work, a novel immobüiIed-cell- film airlift bioreactor (See Figure 3.1.) is developed by employing Cotton cloth sheets to immobiiize yeast ce& by amchment The performance of the immobilized-ceI-nIm bionactor is compared with the comsponduig fiex celi system in both continuons and repeated batch culture modes to evaluate the efnciency and feasibüiPy of the proposed bionactor. A mathematical mode1 is developed to describe the plasmid loss and enzyme production decay kinetics m the immobillled c d system. A general explanation for the enhancement by irnmobilization is sought It is the intent of this work to gain a betw
understanding of the nature of the immobiüÿed recombinant yeast through experiments and modelling. 6.2. Continuous Culture in XmmobiIizeà-Ceil Bioreactor 62.1. Modd Development An idealised modei is w d to characten.ize the Unmobiliwl cell system as jiiustrated in Figure 6.1. As shown in Figure 6.1, the i-d biofilm has a unifonn density of œUs attached to the support and a locally d o m thickness with negiigible interna1 and extemal mas W e r mistance. 'Ihese assurnptions may be justified for the present immobïiized-ceU-film airM bioreactor because of the thin biofilm (les than 2.0 mm ) and suong hydmdynamic Nculation and mixing in the bioreactor. It is ako assumed that no growth merence between the plasrnid-bea~g and plasmid-frez cells ex&&, which was confimied for the present ncombinant yeast in previous studies. Under these assumptions, an identicai specific growth rate for both the biofïim and suspended plasmid- bearing and plamid-Eree ceh in the immobilized-ceiî-fîim biore-r may be justified. The specific growth rate of the immobilized ceil system at a fïxed dilution rate is denoted as in the immobïiized-cetl-fi airlift bioreactor, ceils grow on the cloth film and are continuously detached into the medium due to hydrodynamic forces. It is unlüUely that additional free space wiU be avaiiable for re-entiy of the released œk onto the Wy- covend cloth surface again (Ghose, 1988). huming a constant vaiue of plasmid los
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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
Page 133 and 134: Figure 4.17. Totai Cell Mas at Diff
Page 135 and 136: another recombinant yeast (impoolsu
Page 137 and 138: other recombinant yeast under nonse
Page 139 and 140: 4.3.4. Effixt of Dilution Rate On R
Page 141 and 142: Figure 4.18- Etlects of Mluiioa Rat
Page 143 and 144: Number of Generations - - - - - - *
Page 145 and 146: B Table 4.5. Metabolic Pathway Anal
Page 147 and 148: concentration. But this may be more
Page 149 and 150: [+ Enzyme (ALR) + Enzyme (STR) +Fra
Page 151 and 152: necessary for host ce& to grow in t
Page 153 and 154: Glucoamylase ConcentraUon (unltsll)
Page 155 and 156: [a Selective Medium A Nonseiective
Page 157 and 158: 5.1 Introduction CHAPTER 5 MODELING
Page 159 and 160: handle. excess glucose is femented
Page 161 and 162: The carbon fluxes h m the three met
Page 163 and 164: 53. Modei Simulation in Batch CuItu
Page 165 and 166: 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: It may take several generations for
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 and 218: ecause glucose fermentation dominat
Page 219 and 220: cells. Tests of the proposed model
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
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(continue)
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(continue)
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(continue)
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E.2. Batch Fermentation with Recomb
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(continue)
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(continue) tfhJ 0.5 10.5 12.75 12.5
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(continue)
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E.3.2. Experimental Data (Parker an
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Run No: CALE (Selected Strain. D =
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Run No: CALR 5 (Original Suain, D =
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Run No: CSTR3 (Selected Suain, D =
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(continue)
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Run No: CICR2 (Selected Suain, D =
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Run No: CiCR4 (Selected Suain, D =
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Eh. Repeated Batch Culture in hmobi
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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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