Phenotypic Convergence in Bacterial Adaptive Evolution to Ethanol Stress. Escherichia coli

Although the relationship between phenotypic plasticity and evolutionary dynamics has attracted large interest, very little is known about the contribution of phenotypic plasticity to adaptive evolution. In this study, we analyzed phenotypic and genotypic changes in E. coli cells during adaptive evolution to ethanol stress. To quantify the phenotypic changes, transcriptome analyses were performed. Overall design: We previously obtained 6 independently evolved ethanol tolerant E. coli strains, strains A through F, by culturing cells under 5% ethanol stress for about 1000 generations and found a significantly larger growth rate than the parent strains (Horinouchi et al, 2010, PMID: 20955615). To elucidate the phenotypic changes that occurred during adaptive evolution, we quantified the time-series of the expression changes by microarray analysis. Starting from frozen stocks obtained at 6 time points (0, 384, 744, 1224, 1824 and 2496 hours) in laboratory evolution, cells were cultured under 5% ethanol stress, and mRNA samples were obtained in the exponential growth phase for microarray analysis.

尽管表型可塑性（phenotypic plasticity）与进化动力学之间的关联已引发广泛关注，但学界对表型可塑性对适应性进化的贡献仍知之甚少。本研究针对大肠杆菌（E. coli）细胞在乙醇胁迫适应性进化过程中的表型与基因型变化进行了分析。为量化表型变化，本研究开展了转录组（transcriptome）分析。总体实验设计：我们此前通过在5%乙醇胁迫条件下培养细胞约1000代，获得了6株独立进化的乙醇耐受大肠杆菌菌株A至F，且发现其生长速率显著高于亲本菌株（Horinouchi等，2010，PMID：20955615）。为阐明适应性进化过程中发生的表型变化，我们通过微阵列分析（microarray analysis）对基因表达变化的时间序列进行了定量分析。本实验从实验室进化过程中6个时间点（0、384、744、1224、1824与2496小时）获取的冷冻保存菌种出发，在5%乙醇胁迫条件下培养细胞，并于指数生长阶段收集mRNA样本用于微阵列分析。