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Non Equilibrium Transitions in a Template Copying Ensemble and from noisy cell size control to population growth
Par Arthur GENTHON
Le 26 Novembre 2024 à 11h00 - Laboratoire Jean Perrin - Campus Jussieu - T 22-32- 4e et. - P407
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Résumé
Part 1: Non Equilibrium Transitions in a Template Copying Ensemble
The fuel-driven process of replication in living systems generates distributions of copied entities with varying degrees of copying accuracy. Here we introduce a thermodynamically consistent ensemble for investigating universal population features of template copying systems. In the context of copolymer copying, coarse-graining over molecular details, we establish a phase diagram of copying accuracy. We discover sharp non-equilibrium transitions between populations of random and accurate copies. Maintaining a population of accurate copies requires a minimum energy expenditure that depends on the configurational entropy of copolymer sequences.
Part 2: From noisy cell size control to population growth: when variability can be beneficial
Single-cell experiments revealed substantial variability in generation times, growth rates but also in birth and division sizes between genetically identical cells. Understanding how these fluctuations determine the fitness of the population, i.e. its growth rate, is necessary in any quantitative theory of evolution. Here, we develop a biologically-relevant model which accounts for the stochasticity in single-cell growth rates, birth sizes and division sizes. We derive expressions for the population growth rate and for the mean birth size in the population in terms of the single-cell fluctuations. Allowing division sizes to fluctuate reveals how the mechanism of cell size control (timer, sizer, adder) influences population growth. Surprisingly, we find that fluctuations in single-cell growth rates can be beneficial for population growth when slow-growing cells tend to divide at smaller sizes than fast- growing cells. Our framework is not limited to exponentially-growing cells like E. coli, and we derive similar expressions for cells with linear and bi-linear growth laws, such as M. tuberculosis and fission yeast S. pombe, respectively.