The Investigation of a Possible Adaptive Role for Insertion Sequence Transposition in Evolving Populations of Escherichia Coli
Langeland, James A., 1964-
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Two long-term chemostat populations of E. coli were used to determine if genomic sequence rearrangements due Insertion Sequence transposition correlate with adaptive shifts in the population. One population ran for 753 generations and the other ran for 1730 generations. Total cellular DNA from a cross-section of clones of the populations, as well as DNA from the input strains were restricted with EcoRI and SaIl and electrophoresed on agarose gels. The gels were then blotted onto nitrocellulose and hybridized with radioactively-labeled plasmids containing elements lSI and IS5 as probes. Technical difficulties likely involving the transfer and/or hybridization procedures prevented obtaining adequate results. The hybridizations should have revealed the number and positions of the corresponding IS elements in the genome and allowed comparison between the input strains and the isolated clones. From the frequency of observed transposition it would then have been possible to determine whether transposition of IS elements had been selected for or against during the evolution of the populations. Selection for transposition events would suggest their having an important role in providing genetic variability, while the lack of positive selection would suggest that IS elements are maintained primarily by virtue of their ability to independently replicate.