Date

2009

Author

Açık, Eda

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In this study, effects of different carbon sources and their feeding strategies on recombinant human growth hormone (rhGH) production by Pichia pastoris were investigated by means of cell growth, recombinant protein production and expression levels of hGH and alcohol oxidase (AOX) genes. In this content, firstly, the strain to be used for high level rhGH production was selected between the two phenotypes, i.e., P. pastoris hGH-Mut+ and P. pastoris hGH-MutS. In this selection both phenotypes were compared in two different media containing glycerol/methanol or sorbitol/methanol and P. pastoris-hGH-Mut+ strain grown on medium containing 30 g/L sorbitol with 1% (v/v) methanol was found to have the highest hGH expression level and rhGH production level, 9.84x109 copies/mg CDW and 120 mg/L, respectively. Thereafter, effects of sorbitol, mannitol, fructose, lactose, sucrose, citric acid, lactic acid and acetic acid were investigated by using P. pastoris hGH-Mut+ strain in laboratory scale bioreactors. Among them sorbitol and sucrose were selected to be compared for production in pilot scale bioreactors by adding them batch-wise at the beginning of induction phase with fed batch methanol feeding scheme at μ=0.03h-1. It was shown that sucrose does not support cell growth as sorbitol although it does not repress recombinant protein production. Then three different feeding strategies were applied to develop sorbitol/methanol mixed feeding i) single sorbitol addition at t=0, ii) besides at t=0, adding second batch-wise sorbitol at t=9 h, iii) giving pulse methanol at t=24 h to trigger AOX promoter. These three strategies were compared with a production without addition of co-substrate sorbitol. Substrate consumption, cell growth, recombinant protein production and expression levels of hGH and AOX were investigated for these different feeding strategies. The highest cell concentration was achieved in third strategy as 55 g/L where the highest extracellular rhGH production (301 mg/L) was achieved in the second strategy, with addition of two times of sorbitol. For this highest recombinant protein production case, overall cell and product yield on total substrate were found as 0.17 g/g and 1.71 mg/g, respectively. Moreover, the highest hGH and AOX expression levels were obtained in this strategy.

Subject Keywords

Chemical engineering., Biotechnology.

URI

http://etd.lib.metu.edu.tr/upload/12610881/index.pdf
https://hdl.handle.net/11511/19066

Collections

Graduate School of Natural and Applied Sciences, Thesis