Large-scale (20 l) culture of surface-immobilized Catharanthus roseus cells

Abstract

Surface-immobilized C. roseus cell cultures were grown in a 20-l modified airlift bioreactor operated at 0.51 vvm (k L a ∼ 8 h −1) under various gassing regimes [air, 2% (v/v) and 5% CO 2]. Extracellular ammonium, phosphate, and nitrate ions as well as carbohydrate uptake and pH value of the medium were monitored together with on-line dissolved oxygen concentration, conductivity of the medium, and carbon dioxide production rate (CPR) of the cultures. Cultures supplemented with 2% CO 2 showed higher nitrate (5.0–7.0 m m d −1) and carbohydrate (3.3 g l −1 d −1) uptake rates and biomass production (μ ∼ 0.24 d −1, yield ∼0.33 g dw g CHO −1 and 7.4 g dw L −1) as compared to air (3.6 m m d −1, 2.1 g l −1 d −1; 0.20 d −1, 0.25 g dw g CHO −1 and 5 g dw l −1) and 5% CO 2 (2.0–3.6 m m d −1, 2.0 g l −1 d −1; 0.11 d −1, 0.20 g dw g CHO −1 and 5 g dw l −1) cultures and as reported previously for suspension cultures. In addition, air and 5% CO 2 cultures displayed incomplete carbohydrate uptake and, more important, phosphate and ammonium ion release into the medium at the end, which was ascribed to loss of viability. This was not observed for 2% CO 2 immobilized bioreactor as well as shake flask control suspension cultures, which suggests that sparged C. roseus surface-immobilized cell cultures require 2% CO 2 supplementation of the gas phase for both maximum growth and retained viability. The maximum CPRs of all cultures were in the same range (2.1–2.8 m m CO 2 l −1 h −1). However, the estimated maximum specific CO 2 production rates of 2% CO 2 and 5% CO 2 immobilized cultures (0.6 m m g dw −1 h −1) were lower than those found for air-sparged immobilized cultures (1.0–1.3 m m g dw −1 h −1). These rates are significantly higher than those reported in the literature for C. roseus cell suspension cultures performed in bioreactors gassed with air (∼0.2–0.55 m m g dw −1 h −1) .