Escherichia coli strain:K-12 MG1655 Variation

Although the evolution of organisms is predicted to be driven and constrained by chance, natural selection and evolutionary trajectories, specifically, how the evolutionary trajectories affect evolutionary outcomes remains understudied. Here, we report a two step experimental evolution study showing that different kanamycin exposure regimes lead to divergent evolutionary trajectories that significantly affect the adaptation rates of Escherichia coli to antibiotics. Populations under mild, periodic or irregular selection regimes evolved similar level of resistance, while populations under strong selection displayed the highest level of resistance in the antibiotic environment. Whole-genome sequencing revealed that only the populations under strong selection acquired SNP mutations in the gene crl. Notably, in the absence of antibiotics, populations with different selection histories exhibited significant differences in antibiotic resistance and adaptive rates. These differences were driven by divergent resistance evolutionary trajectories, even though the populations reached similar levels of resistance under differing selection regimes.