AGUILAR-ROCA, Nancy; LONG, Tony; BENNETT, Al; University of California, Irvine; University of California, Irvine; University of California, Irvine: Genomic changes during adaptation to variable temperatures in Escherichia coli

Most organisms live in thermally variable environments and understanding the genetic basis of adaptation to variable temperatures has been made is now becoming possible by high-density arrays and sequenced genomes. DNA high-density arrays were used to examine insertion and deletion events in six independently derived lines of Escherichia coli that evolved for 2000 generations in a fluctuating temperature environment (daily oscillations between 32 and 42^oC). Genomic DNA from these derived lines that had evolved for 2000 generations in oscillating temperatures was radiolabelled and hybridized to Sigma-Genosys nylon membrane arrays. Spot intensity differences between the derived lines and a corresponding ancestor were used to identify the insertions and deletions of major segments of DNA in the bacterial chromosome. A deletion event occurred in each of two lines in different regions of the genome. All of the lines had a significant increase in fitness at both 32 and 42^oC relative to the ancestor, but the deletion event does not appear to be an important factor in changes in fitness at either 32 or 42^oC. The deletions included genes involved in iron transport and glycolate metabolism. Although the deletions were neither beneficial or detrimental under the culture conditions used, under different culture conditions fitness may be compromised. These results suggest that deletions are one mechanism of trade-offs during evolutionary adaptation to a specific environmental condition. Supported by NSF Grant IBN9905980 and NASA Grant 632731.