Connections among Genotype, Phenotype and Fitness in Escherichia coli High Temperature Lines

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An improved understanding of the process of evolutionary genetic adaptation must rely in part on a better understanding of how genetic changes are linked to changes in structural and functional characteristics of organisms (phenotypes) that result in improved reproductive success (i.e., fitness). However, the relationship between genotype and phenotype is not well understood, limiting an understanding of the evolutionary process. The work funded by this award will investigate the relationship between genotype and phenotype on an unprecedented scale in the bacterium Escherichia coli. The bacterium has been adapted through artificial selection experiments to thermal stress (42.2 C) for one year in over 100 replicate populations. A clone from each population has been genotyped completely by genomic sequencing. This grant will characterize the phenotypes of these replicate populations and then relate these phenotypes explicitly to the known genotypes. The phenotypes that will be measured include patterns of gene expression and features of cell metabolism. Of particular interest will be a contrast between clones that adapted by mutations in either the transcriptional termination gene rho or the RNA polymerase subunit gene rpoB. The work will determine whether these different genetic solutions lead to similar functional changes in phenotypes and whether the two adaptive pathways are mutually exclusive. To address the latter issue, mutations of both rho and rpoB will be introduced into a single genetic background, and the evolutionary fitness of double mutants will be determined at high temperature. By characterizing both phenotypic changes and genetic interactions associated with adaptation, this work will impact the heart of evolutionary theory, including classical views on the adaptive process. In addition, this project will continue a successful outreach project that introduced K-12 teachers to lab modules that facilitate "hands on" teaching of evolution in the classroom, based on the E. coli model.