Date

2012

Author

Zerze, Halime Gül

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Recombinant human growth hormone (rhGH) production levels and bioprocess characteristics were investigated for two recombinant Pichia pastoris strains. In the first part of the study, feeding strategies for semi-batch operations were developed in pilot scale bioreactors to improve rhGH production under strong methanol inducible alcohol oxidase I (AOX1) promoter, by previously constructed P. pastoris M13 strain (pPICZαA::hGH-Mut+). Three different methanol feeding strategies together with mannitol co-feeding named as MM1, MM2 and MM3 were performed. In MM1, methanol was fed to the bioreactor with a pre-determined specific feeding rate of µM0=0.03 h-1; whereas, three pulses of mannitol was introduced at t=0, 8, and 15 h and the mannitol concentration in the bioreactor increased to 50 g L-1. In MM2, the semi-batch bioprocess was started with 50 g L-1 mannitol concentration at t=0 h and kept constant at this concentration until t=6 h; in the following period until t=19.5 h, methanol was fed with a pre-determined specific feeding rate for µM0=0.03 h-1; and then in the third period, by t=20 h dynamic methanol feeding was employed for constant µ=0.03 h-1. In MM3, the same mannitol feeding strategy was performed as in MM2, together with the pre-determined methanol feeding for µM0=0.03 h-1, until t=12 h; thereafter, for constant µ=0.03 h-1 dynamic methanol was feeding employed. Throughout the experiments, the cell, mannitol and methanol concentrations, rhGH, and organic acid concentrations; AOX and protease activities were experimentally determined. The highest rhGH concentration was obtained in the MM2 strategy as CrhGH=1.2 g L-1; whereas the highest cell concentration was reached in MM3 as CX=157 g L-1. Further, the highest overall product yields on substrate and cell, YP/St and YP/X, were obtained in MM2 respectively as 4.02 mg g-1 and 10.67 mg g-1. In the second part of study, recombinant P. pastoris G7 strain, which provides constitutive rhGH expression under glyceraldehyde-3-phosphate dehydrogenase (GAP) promoter, was designed and constructed. After selection (how?) of the microorganism having the highest production potential (G7), two different glucose feeding strategy, namely G1 and G2, were employed to investigate and improve the rhGH production. In G1, glucose was fed with the pre-determined µG0=0.2 h-1 until t=6 h; where, with a step-down operation the pre-determined µG0 decreased to µG0=0.03 h-1 throughout the bioprocess. Based on the findings of the G1 strategy, in G2, glucose was fed with the pre-determined specific growth rate of µG0=0.2 h-1 until t=3 h; and than proceeded with constant glucose feeding. The highest CX and CrhGH were obtained as 90 g L-1 and 0.2 g L-1 in G2; moreover, the overall yield coefficients YX/S, YP/S, and YP/X were obtained, respectively, as 0.48 g g-1, 1.21 mg g-1, and 2.53 mg g-1.

Subject Keywords

Somatotropin., Recombinant human somatotropin., Pichia pastoris.

URI

http://etd.lib.metu.edu.tr/upload/12615249/index.pdf
https://hdl.handle.net/11511/22239

Collections

Graduate School of Natural and Applied Sciences, Thesis