Feeding cycle cell culture

Typically, the number of seed steps is impacted by the inoculation ratio, that is, the volume expansion factor between two seed steps. Depending on the duration of seed cultures and the cycle time of the main fermentation or cell culture, seed trains may feed into one or multiple bioreactors. Cycle time defines the time window between start of batch N and batch Af -I-1. 

Figure 3.6. SDS-PAGE gel of samples taken during affinity precipitation of avidin from cell culture supernatant. M molecular mass markers, Ref avidin containing feed, SI feed after affinity precipitation, S2 and S3 supernatants obtained during washing cycles, S4 first dissociating buffer supernatant (release of avidin), S5 second pr dpitation of the AML from dissociating buffer, B buffer samples (reproduced with p>ermission from reference 25).

Figure 2. Changes of cell density and COj-concentration in outlet gas of the culture vessel Chlorella sp. UKOOl strain was cultured in the photobioreactor, tmder condition of light (lOh)-dark (14h) cycles with artificial halogen supply and exhaust gases and the feed lamps at 35 U. COj concentration of...

The model-based dynamic optimisation results that were obtained from a fixed feed composition, same initial condition as the batch culture, and a feeding interval of 6-12 h, suggested an optimal cell cycle-arrest time at 126 h and supplementation with feed from 48 h onwards. The results of three different fed-batch cultures with identical supplementation strategies but various cell cycle-arrest times are shown in Fig.3. The viable cell concentration, Xy, was closely predicted up to about 80 h. However, after lOOh, Xv decreased significantly in all three cultures. The predicted MAb concentration was in accordance with the experimental results with only a slight under-prediction around 80-100 h. Both model predictions and experimental results indicated a small difference in MAb yield when the cultures were arrested at different times. The optimised fed-batch experiments involved a total of 9 shake flask cultures so the... 

The bacteria s spatial juxtaposition (awareness relative to other bacteria) may also be hindered by turbulence. In the worst-case scenario, the bacteria are not able to make significant contact and are not able to achieve the necessary cell density for optimal operation (Bliem and Katinger, 1988b) or are not able to make syntropic relationships with other bacterial cultures (Hoffmann et al., 2008). The result is that start-up performance is very poor with minimal or insignificant conversion while long-term performance is not hindered in a bacterial mixture that allows competition and has at least one shear-tolerant species. Conditioning with feast and famine cycles improved recovery time and tolerance to feed and shear shocks (Hoffmann et al., 2008). 

Figure 3 Fermentation modes for recombinant bacteria, yeast, and animal cells. On the left-hand side, the feed streams and harvesting streams are schematically shown for the batch, fed-batch, and continuous cultivation of microorganisms. On the right-hand side, the product concentration and the cell density are shown. For batch and fed-batch a discontinuous product concentration profile is obtained. With constitutive expression of a product, the product concentration is dependent on the cell density. Product is present in the culture supernatant during the whole production cycle and thus more susceptible to degradation. When the product formation is induction controlled, the production concentration raises sharply after addition of the inductor. The residence time of the product in the bioreactor is reduced. For continuous culture a constant product concentration profile is maintained over the entire production cycle. The residence time of the product in the bioreactor depends on the harvesting time and is shortest tor all fermentation modes when harvesting is continuously performed. Changing the mode of production can highly influence the composition of feed for preparative chromatography.

---