Determination of division rates of rCHO cells in high density and immobilized fermentation systems by flow cytometry.

As most high density and immobilized fermentation systems do not allow the direct quantitative determination of cell density, two flow cytometric methods (the determination of incorporation of bromodeoxyuridine into newly synthesized DNA and the increase in mitotic cells by colchicine blockage) were evaluated as to their suitability to measure true division rates of cells in bioreactors. The BrdU method gave division rates identical to the growth rates measured by cell count, while the colchicine block method gave values that were lower and varied with the cell line. This is due to the cytotoxicity of colchicine and makes a calibration of the method for each cell line necessary. Both methods have been successfully used to measure division rates of rCHO cells immobilized in an alginate matrix as well as in macroporous carriers in a fluidised bed system and in dialysis culture.