Plasmid burden in chemostat culture of Escherichia coli: Its effect on the selection for overproducers of host enzymes.

The effect of plasmid-mediated metabolic burden of on the expression of the host genes and its consequences on the plasmid maintenance were studied in carbon-limited chemostat culture of Escherichia coli 1EA(pBR322) subject to selection for strains overproducing chromosomally coded ribitol dehydrogenase. The chemostat population became rapidly heterogeneous and the competition among evolved strains was found to be crucial for the kinetics of the plasmid loss from the culture. The selective disadvantages in growth rate associated with plasmid carriage in the parent-like and ribitol dehydrogenase-overproducing strains was estimated. (c) 1993 John Wiley & Sons, Inc.