Selection experiments with random sequence clones in E. coli

Previous experiments suggested that expression of random sequence clones in Escherichia coli can enhance growth of cells, i.e. they can provide a direct fitness advantage. However, these findings have been questioned, regarding potential confounding effects of the clone mixtures and a possibly negatively acting peptide expressed from the cloning vector.

Here we performed controlled competitive growth assays using a defined subset of random sequence clones representing a spectrum of fitness effects. Experiments across multiple conditions, including two different growth cycle durations, induction states, and replicate sets, showed high technical reproducibility and consistent clone-specific growth trajectories for the majority of the clones, but for some also influences of genomic background and experimental conditions.