RIEHLE, Michelle M; BENNETT, Albert F; LONG, Anthony D; Univ of California, Irvine and Univ. of Minnesota; Univ. of California, Irvine; Univ. of California, Irvine: Differential Patterns of Gene Expression and Gene Complement in Laboratory-Evolved Lines of E. coli

Combining laboratory natural selection and genomics with comparative physiology creates a powerful tool for understanding organismal responses to long-term temperature stress. Although bacteria are not yet commonly used in comparative physiology, they are an ideal organism for laboratory natural selection and genomics. Bacteria can be maintained in large populations while occupying limited lab space, have short generation times, are well characterized physiologically, biochemically, and genetically, are readily frozen and revived from the freezer, and bacterial fitness can be assayed by direct competition between ancestral and derived lines. Using six lines of Escherichia coli grown at 41.5�C for 2000 generations and thirty E. coli lines grown at 20�C for 2000 generations we measured both phenotypic and genotypic changes to determine the degree to which the adaptation to temperature is replicable across independently derived lines. All lines show significantly (p<0.05) increased fitness in their selective environment, with fitness increases at high temperature of greater magnitude than those at low temperature. Measurement of gene expression phenotype indicates that 4 to 5 times more genes show replicable expression change across high temperature derived lines than expected due to chance. At the level of gene copy number, duplication events predominate during high temperature adaptation, while deletion events predominate during cold temperature adaptation (p<0.05). Three of six high temperature derived lines show gene duplications in the same genome region, while six of thirty cold adapted lines show deletion in the same region, both suggesting convergent evolution and moderate evolutionary replicability at the level of gene copy number. These results are an example of the powerful insights that can be discovered by combining the tools and analyses of many biological disciplines including genomics, evolutionary biology, and comparative physiology.