The growth behavior of a mixed culture of plasmid-free and plasmid-containing (YEp352) Escherichia coli HB101 cells in free suspension and immobilized conditions was studied experimentally. It was found that immobilization in calcium alginate beads delayed the reduction of the plasmid-containing fraction for a period of time inversely related to the total number of cells initially immobilized. A simple unstructured model that assumes compartmentalization of cells in the immobilization matrix at the beginning of growth gave a fit which was in good agreement with the data.

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