Bacteria play critical roles in many environmental processes, in human health and disease, and in biotechnology. It is important, therefore, to understand the processes by which bacteria change over time, and to measure the rates of change in their genes and ecological functions. Reseachers at Michigan State University will study evolutionary changes in replicate experimental populations of the bacteria species Escherichia coli, as they evolve in a controlled laboratory environment for thousands of bacterial generations. To measure adaptation, the researchers place the bacteria from later generations in competition with the ancestral strain, which is stored frozen and revived for these experiments. To quantify genetic evolution, the researchers will sequence the genomes of bacteria from many time points and compare them to the ancestor's DNA sequence. These analyses will provide unique information about the rates, mechanisms, effects, and predictability of bacterial evolution. The knowledge gained will benefit both science and society because bacteria are key players in the environment, health, and technology.
This experiment provides a unique study of bacterial evolution by generating exceptionally long time-series of samples from 12 replicate populations, all founded from the same strain of E. coli and maintained in identical environments. The research team will propagate the populations by transferring them every day into fresh medium; every 500 generations, samples are stored frozen, where they remain viable. Over the next decade, the experiment will surpass 85,000 generations. The frozen samples will be used to analyze the dynamics of adaptation by natural selection, the coupling of phenotypic and genetic evolution, and the repeatability of evolutionary changes. Research questions to be addressed include: Will the fitness of the evolving bacteria relative to their ancestor continue to increase indefinitely? Do the trajectories for relative fitness and genomic evolution have similar curvatures, or are they discordant? How repeatable are fitness gains and genomic changes across replicate populations? The biological samples and datasets generated in this project will be shared with the scientific community.
