Strategies for Improved dCO2 Removal in Large-Scale Fed-Batch Cultures

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• 作者：Sigma S. Mostafa and Xuejun (Sherry) Gu
• 刊名：Biotechnology Progress
• 出版年：2003
• 出版时间：February 2003
• 年：2003
• 卷：19
• 期：1
• 页码：45 - 51
• 全文大小：153K
• 年卷期：v.19,no.1(February 2003)
• ISSN：1520-6033

文摘

Carbon dioxide buildup in large-scale reactors can be detrimental to cell growth andproductivity. In case of protein X, a therapeutic glycoprotein, when cultures were scaledup from bench scale to the pilot plant, there was a 40% loss of specific productivity.The dissolved CO₂ (dCO₂) level was 179 ± 9 mmHg at the pilot plant scale and 68 ±13 mmHg at bench scale. The authors proposed a comprehensive approach to maintaindCO₂ levels between 40 and 120 mmHg throughout the 14-day fed-batch process. Acell-free experiment was used to investigate the impact of the following parameterson dCO₂ removal: (1) sparge rate, (2) agitator speed, (3) bubble size, (4) bicarbonateconcentration, (5) impeller position, and (6) aeration rate at the headspace of bioreactor.dCO₂ was measured using a fiber optic based probe. dCO₂ removal rate was a strongfunction of sparge rate and a weak function of agitator speed. Bubble size wasmodulated by the presence or absence of a sparge stone (10 m pore size, 1 cm pipei.d.). Open pipe provided 3- to 4-fold better dCO₂ removal for the same mass transfercoefficient (k_La) value. A mathematical model and a bench-scale experiment indicatedthat the benefit of a lower level of sodium bicarbonate in the culture medium wastransient for batch and fed-batch cultures. Thus, this strategy was not used at pilotscale. Decreasing top impeller position improved k_La of dCO₂ by 2-fold. Changingheadspace aeration rate from 0.02 to 0.04 vvm had no impact on dCO₂ removal. Twopilot runs were conducted using (A) open pipe and (B) antifoam in the presence ofsparge stone, both in conjunction with lower impeller position. The presence of antifoammay interfere in product purification; however, demonstration of antifoam removalcan be difficult. Open pipe allowed an alternative to using antifoam, as foam levelwith open pipe was significantly less. Both strategies successfully reduced dCO₂ levelby 2.5-fold (179 ± 9 vs 72 ± 9 mmHg). Titer at day 10 of culture improved by 1.5-fold.Specific productivity improved by 41%. Historically, cultures were harvested aroundday 9-11 because of the high amount of foam; both strategies allowed the cultures tobe extended up to day 14, resulting in 2-fold higher titer compared to that of thehistorical control without compromising protein quality.