Analyses of intercellular interaction and genome structure change during heat tolerant evolution by using experimental evolution system with Escherichia coli

我们对细胞和大肠杆菌的动力学进行了研究。大肠杆菌种群水平在适应热应激（高温; 39度以上）。首先建立了维持比生长速率的连续传代培养体系，然后将E.将大肠杆菌培养物置于高温（高于过去温度2度）下。我们可以进化出E.大肠杆菌能接受45 ℃的最高温度条件。大肠杆菌能在最小条件培养基中存活。在39 ℃适应过程中，温度过渡后，生长速率迅速下降，细胞内绿色荧光蛋白（GFP）荧光标准差下降。大肠杆菌在2~ 7 d内生长迅速，10-20 d后生长速度恢复，GFP的SD值下降，并收敛到39度特异值。这些结果表明，温度变化引起了细胞内环境的变化，可能导致了E. coli群体，然后用E.大肠杆菌多样性。在45度适应初期，E. coli能以密度依赖方式生长。这种依赖性来源于E.因此，温度变化可能诱导群体感应。我们一直在从大肠杆菌中寻找相应的分泌因子。coli培养上清液。此外，E.随着温度的升高，大肠杆菌细胞内鸟嘌呤和胞嘧啶的含量均呈下降趋势。这些结果表明，E.大肠杆菌的多样性和/或相互作用可能带来的。通过进化表型的固定过程，观察到了基因组DNA含量增加和G/C含量降低。

We have researched about the dynamics both of cellular and E. coli population level during adaptation to heat stress (high temperature; above 39 degree). First, we constructed the serially transfer culture system maintaining specific growth rate, then transferred E. coli culture to high temperature (2 degree above past temperature). We could evolve E. coli to accept 45 degree condition that was highest temperature E. coli could survive in minimum conditioned medium. During 39 degree adaptation, just after temperature transition, growth rate decreased rapidly and standard deviation of fluorescence of cellular green fluorescence protein (GFP) of E. coli population enhanced in 2~7days, then growth rate recovered and SD of GFP was decreased for 10-20 days and converged to 39 degree specific values. These results indicated that temperature shift induced diversity of intracellular conditions that might bring the recovery of plasticity of E. coli population, and then adaptation was facilitated by E. coli diversity. At the early stage of 45 degree adaptation, E. coli could grow cell density dependent-manner. This dependency was derived from secreted factors from E. coli, therefore, temperature shift might induce quorum sensing. We have been searching corresponding secreted factors from E. coli culture supernatant. Moreover, average genome DNA content in E. coli cell increased in proportion to adaptation to higher temperature, and interestingly content both of guanine and cytosine decreased according to adaptation to higher temperature. Our results suggested that heat tolerant adaptation and evolution of E. coli might be brought by diversification and/or interaction among E. roll population, and genome DNA content increment and G/C content decrement were observed through fixation process of evolved phenotype.