High throughput approaches to study laboratory-based evolution of E. coli for enhanced growth at low pH

Laboratory-based evolution has become a widely used method to explore fundamental questions about evolution as a process, and is also a powerful tool to study the link between genotype and phenotype. We have evolved six populations of E. coli MG1655 by iterative growth and dilution at pH 4.5 over five months, keeping a frozen fossil record of intermediate populations during this process. Whole genome sequencing of the evolved strains revealed many striking similarities in the evolutionary trajectories in the evolved strains; for example, mutations in arcA are common and may cause loss or alteration of function. We are interested in exploring the impact of different parameters on evolutionary trajectories, but as evolution experiments take a long time, we are currently investigating the potential of traDIS to replicate evolution experiments in a relatively short time frame. Since TraDIS provides a measure of relative contributions to fitness of each gene (by comparison of read counts after growth in two conditions), in principle it should be possible to use TraDIS to identify genes whose loss of function provides a fitness benefit. Here we compare the outcome of these two techniques and present our latest results.