An amplified NS0 cell line transfected with a vector expressing a humanized monoclonal antibody (MAb) against CD‐18 and glutamine synthetase (GS) was cultivated in a 1.5 L fed‐batch culture using a serum‐free, glutamine‐free medium. Concentrated solutions of key nutrient components were fed periodically using a simple feeding control strategy. Feeding amounts were adjusted daily based on the integral of viable cell concentration over time (IVC) and assumed constant specific nutrient consumption rates or yields to maintain concentrations of the key nutrient components around their initial levels. On‐line oxygen uptake rate (OUR) measurement was used to aid empirically the adjustment of the feeding time points and amounts by inferring time points of nutrient depletion. Through effective nutritional control, both cell growth phase and culture lifetime were prolonged significantly, resulting in a maximal viable cell concentration of 6.6 × 109 cells/L and a final IVC of 1.6 × 1012 cells‐h/L at 672 h. The final MAb concentration reached more than 2.7 g/L. In this fed‐batch culture, cellular metabolism shifts were repeatedly observed. Accompanying the culture phase transition from the exponential growth to the stationary phase, lactate, which was produced in the exponential growth phase, became consumed. The time point at which this metabolism shift occurred corresponded to that of rapid decrease of OUR, which most likely was caused by nutrient depletion. This transition coincided with the onset of ammonia, glutamate and glutamine accumulation. With removal of the nutrient depletion by increasing the daily nutrient feeding amount, OUR recovered and viable cell concentration increased, while cell metabolism shifted again. Instead of consumption, lactate became produced again. These results suggest close relationships among nutrient depletion, cell metabolism transition, and cell death. © 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 783–792, 1997.

Polyvinylpyridine (PVP) and activated carbon were examined for the adsorption characteristics pertinent to their application in lactic acid fermentation. For PVP the linear adsorption constant, K aii , was between 0.7 and 1.0 for an equilibrium pH range of 3 to 9. The pH was adjusted by acid/base addition, similar to pH control in fermentation. The values of K^ in the pH-adjusted systems were much lower than that reported for pure lactic acid solutions, i.e., about 9.7. Furthermore, no clear effect of pH was observed. These are attributed mainly to the competition of anions (Cl~ and lactate) for the adsorption sites of protonated pyridinal N. Its adsorption capacity was also found to decrease with the base regeneration (by about 14% each time) after being contacted with the culture broth. These limit its potential application in lactic acid fermentation. Activated carbon was much more effective in lactic acid/lactate adsorption than PVP. At pH 5.5 (optimal for fermentation), the value of /f ad of activated carbon was about 7. The adsorption further favored lower pH under acid (HC1) addition. Activated carbon has been reported to adsorb glucose. However, the presence of glucose in 0-70 g/L was found in this study to have an insignificant effect on lactate adsorption. Cells of Lactobacillus delbrueckii also adsorbed rapidly on activated carbon. This cell adsorption had a negative effect on lactate adsorption.