Evolution of carrying capacity in evolution experiments focusing on a single locus on the Escherichia coli chromosome

We performed a series of evolution experiments, the results of which illustrated the relationship between mutations and increased carrying capacity (K). Performing an evolution experiment with repeated cycles of mutation by PCR and selection makes it possible to obtain results over shorter culture durations than in methods reported previously relying on spontaneous mutation and selection. We constructed random mutant populations of Escherichia coli in which members differed only in part of the genomic copy of the glutamine synthetase gene and performed daily serial transfer culture where the populations were in K-selected environments. The value of K in this system was increased by 10(5)- to 10(8)-fold relative to the parent clone, which was achieved by four randomly introduced mutations. This method can be applied to any gene and will be useful for analyzing a number of important issues in evolutionary biology.