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

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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.