Phenotypic Convergence in Bacterial Adaptive Evolution to Ethanol Stress

Bacterial cells have a remarkable ability to adapt and evolve to environmental changes, a phenomenon known as adaptive evolution. Adaptive evolution can be explained by phenotypic changes caused by genetic mutations, and by phenotypic plasticity that occur without genetic alteration, although far less is known about the contributions of the latter. In this study, we analyzed phenotypic and genotypic changes in Escherichia coli cells during adaptive evolution to ethanol stress. Phenotypic changes were quantified by transcriptome and metabolome analyses and found similar among independently evolved ethanol tolerant strains. The contribution of identified mutations in the tolerant strain was evaluated by using site-directed mutagenesis, which suggested that the fixation of these mutations cannot fully explain the observed ethanol tolerance. The phenotype of ethanol tolerance was stably maintained after an environmental change, suggesting that a mechanism of non-genetic memory contributed to at least part of the adaptation process.