Cell culture, batch size

TABLE 4.9. Batch size of cell cultures and estimated time required for fermentation... 

Flow cytometry [141, 142] is a technique that allows the measurement of multiple parameters on individual cells. Cells are introduced in a fluid stream to the measuring point in the apparatus. Here, the cell stream intersects a beam of light (usually from a laser). Light scattered from the beam and/or cell-associated fluorescence are collected for each cell that is analysed. Unlike the majority of spectroscopic or bulk biochemical methods it thus allows quantification of the heterogeneity of the cell sample being studied. This approach offers tremendous advantages for the study of cells in industrial processes, since it not only enables the visualisation of the distribution of a property within the population, but also can be used to determine the relationship between properties. As an example, flow cytometry has been used to determine the size, DNA content, and number of bud scars of individual cells in batch and continuous cultures of yeast [143,144]. This approach can thus provide information on the effect of the cell cycle on observed differences between cells that cannot be readily obtained by any other technique. 

A problem with in vitro cultured hybridomas is low antibody 3held, typically in the range 20-100 mg/litre compared to the ascites in vivo route of 5-10 g/litre. Regulation in the use of experimental animals in many countries now means that the ascitic route is not an option, but to put matters in perspective 1 g of mAb obtainable from 100 mice can be produced in 10-20 litres of culture. This difference can be dramatically reduced if perfusion systems with high cell densities (over 5 X lO ml) are used. When mAbs are needed for research or diagnostic purposes then batches up to only 200 mg are needed and this can be achieved in 2-5 litres of culture. However for in vivo diagnostics and therapeutics where batch sizes of 10-100 g are required then the scale-up to fermenter/airlift reactor or perfusion systems is a necessity. 

Compeau et al. (1990) reported a full-scale slurry-phase PCP remediation. The system consisted of soil washing and screening and resulted in clean soil and wash solution. The wash solution was a slurry containing PCP and < 60-mesh-size soil particles at approximately 20% solids concentration. Slurry was treated subsequently in on-site slurry-phase bioreactors. A 50 m3 slurry reactor was operated in batch mode and inoculated by an uncharacterized PCP-mineralizing culture (107 cells/ml of slurry). After 14 days, 370mg PCP/kg slurry had been degraded to below 0.5 mg/kg. For effective biogradation to occur, inoculation was required. 

Mavituna, F. and J. M. Park, "Size Distribution of Plant Cell Aggregates in Batch Culture," Chem. Eng. J. 35 (1987) B9-B14. 

Figure 6.23 illustrates simulation curves of a batch culture, which show the changes of mass (Cx/CXmax), number (Cx/CXBmax), and size of cells (Cx/CXg), and the substrate concentration (Cs/CSq) in dimensionless form. This curve shows the following features ... 

Unstructured distributed models such as Monod s equation satisfactorily predict the growth behavior in many situations. However, they cannot account for lag phases, sequential uptake of substrates, or changes in mean cell size during the growth cycle of a batch culture. Structured models recognize the multiplicity of cell components and their interactions. Many different models have been proposed based on the assumptions made for cell components and their interactions. 

---