RIEHLE, M. M.*; BENNETT, A. F.; LONG, A.D.: Evolutionary changes in stress gene expression in thermally adapted lines of Escherchia coli .

Stress gene expression and stress proteins are widely known to increase in response to thermal stress, playing roles in the degradation or refolding of proteins damaged by environmental stress and in preventing the aggregation of damaged proteins. The response of individual genes and their protein products to thermal stress has been thoroughly studied; however, the application of a whole genome approach allows simultaneous investigation of all genes associated with thermal stress. We used DNA high-density array technology and data from expression profiling experiments to address the hypothesis that natural selection leads to changes in stress gene expression during the adaptation to a constant high temperature (42°C) in experimentally evolved lines of Escherichia coli . The 8 highly conserved chaperone genes ( dnaK/hsp70, mopA/hsp60 etc.) were found to have increased expression as a result of high temperature adaptation: mean expression of the 6 replicate lineages was 5.5 fold higher than the average gene vs 4.7 fold higher than the average gene in their common ancestor (p<.03). In addition to being highly expressed at high temperature, the 33 stress genes examined, including 8 highly conserved chaperone genes and 25 other heat inducible genes, exhibit significant (p<.02) differences in expression between the group of high temperature adapted lines and their ancestors. A number of genes appear to be targets of selection during high temperature adaptation, including genes involved in the extracytoplasmic stress response. Supported by an NSF Predoctoral Fellowship and a DDIG to MMR and NSF Grant IBN 9905980 to AFB.