Riehle, M. M.*; Bennett, A.F.; Long, A.D.: Genetic analysis of the adaptation to temperature stress: a role for gene duplications

Additional copies of certain genes or gene regions have been implicated previously as instrumental players in organismal adaptation to environmental stresses, especially as a means for gene amplification in microorganisms. Six lines of high temperature (41.5�C) adapted Escherichia coli were screened for gene duplications and deletions using DNA high-density array technology. Three of the six selected lines contain a region of gene duplication at least 23.7 kb in size at the 59th minute of the chromosome. This duplicated region contains genes that have previously been shown to enhance stationary phase survival under benign or stressful conditions and to help in the repair of damaged proteins. Expression of two candidate genes in the lines with the gene duplication is significantly elevated over ancestral expression levels. In the two cases where the duplication at 2.85MB has been furthered characterized, the timing of the genome reorganization is coincident with significant increases in relative fitness. These six lines of high temperature adapted bacteria have now spent 2000 additional generations back at their ancestral temperature of 37�C and we will determine (1) how their relative fitness has changed at both high temperature and at 37�C and (2) whether the bacteria still contain the duplication at the 59th minute that originated during the 2000 generations at high temperature or have they reverted back to their ancestral haploid state. Supported by NSF-IBN 9507416, NSF-IBN 9905980 to AFB, NIH-GM 58564 to ADL and a NSF Predoctoral Fellowship to MMR.