Escherichia coliHost Cell Modifications in Continuous Culture Affecting Heterologous Protein Overproduction: A Population Dynamics Study

摘要

AbstractThere are many published studies of plasmid segregational instability inEscherichia coliin the literature. However, the formation of plasmid‐free segregants can be controlled by the addition of selective chemical agents like antibiotics. This solution has become commonplace in both the laboratory and industry. On the other hand, host cell modifications, which result in low production of plasmid‐encoded protein and lead to loss of culture productivity, have not been adequately addressed. Continuous culture of an inducible (ptac)Escherichia colivector containing strain, RB791(pKN), was characterized by strong dynamic changes in the cell population and product (β‐lactamase) expression. Long‐term cultivation resulted in the loss of high‐level production ofβ‐lactamase. Loss of productivity was not due to the formation of plasmid‐free cells or structural modifications to the plasmid; instead, continuous operation resulted in a culture dominated by irreversibly altered, low‐producing cells. Two distinct classes oflac−mutants which inhibited induction were id