Evolution of gene expression during long term coexistence in a bacterial evolution experiment

We used microarrays to study the evolution of gene expression in two bacterial ecotypes that coexisted for more than 35000 generations of experimental evolution in an extremely simple environment We sampled four clones from each of two lineages at generations 6,500, 17,000 and 40,000 from the polymorphic Ara-2 population of the E. coli long-term evolution experiment. The four clones from each lineage and generation were mixed equally and used for global expression profiling, growth assays and competition experiments. Global expression profiles and growth assays were also performed on the ancestral strain. RNA extractions were done using cells in mid-exponential growth in the same glucose-limited minimal medium used in the evolution experiment. Global expression profiles were obtained by using Affymetrix arrays, with 5 or 6 biological replicates for each lineage-generation sample.