Competition between strains of Escherichia coli with and without plasmid RP4 during chemostat growth

Escherichia coli strains J53(nal) and J53(RP4) were grown together in glucose-limited continuous cultures. Based on the measured growth kinetic constants of the two strains, take-over of the cultures by J53(RP4) was predicted. However, in practice, an initial period of predominance by J53(RP4) was always followed by a prolonged period in which relative numerical proportions of the two strains oscillated widely. This period of oscillation was removed or greatly reduced when the difference between the predicted growth-rate potentials of the two strains was increased by selection of a chemostat-adapted variant of J53(RP4).