Chromosomal Changes during Experimental Evolution in Laboratory Populations of Escherichia coli

Short-term rates of chromosome evolution were analyzed in experimental populations of Escherichia coli B that had been propagated for 2,000 generations under four thermal regimens. Chromosome alterations were monitored in 24 independent populations by pulsed-field gel electrophoresis of DNA treated with five rare-cutting restriction enzymes. A total of 11 changes, 8 affecting chromosome size and 3 altering restriction sites, were observed in these populations, with none occurring in strains cultured at 37°C. Considering the changes detected in these experimental populations, the rate of chromosome alteration of E. coli is estimated to be half of that observed in experimental populations of yeast.