Congratulations to our new doctor Thomas Julou who graduated on June 9th 2011 !
Her thesis defense took place at the Ecole Normale Supérieure Physics Departement in Paris.
« Evolution, competition and cooperation in bacterial populations »
Members of the Jury
Didier Chatenay (CNRS 3231, Paris), President
Ivan Matic (Inserm U1001, Paris)
Sam Brown (University of Edinburgh, UK)
Pierre Cornelis (Vrije Universiteit Brussels)
David Bensimon (CNRS, ENS Paris), Supervisor
Nicolas Desprat (Université Paris Diderot)
The interplay of environment, heritability, and stochasticity results in the development of different individuals starting from a given genotype. This phenotypic variability affects how natural selection acts on genetic variability. From a general perspective, I aim at studying the impact of phenotypic variability on adaptive dynamics.
In the first chapter, I report on the design of an evolutionary experiment in a structured environment using Escherichia coli. The trait under selection is resistance to high temperature. In particular, we study the effects of high temperature on chemotaxis, as well as the impact of acclimation on growth and survival at high temperature.
The second chapter is about the development of a microbial population measurement device dedicated to diluted populations. This continuous, non-invasive measurement has a low detection limit that depends on the species. For the model species Escherichia ecoli, the limit is ca. 5000/mL which represents a 100-fold improvement compared to classical photometric methods.
In the third chapter, we study the distribution of pyoverdine between individuals of a clonal population of Pseudomonas aeruginosa. The variability of the concentration of this siderophore is much greater than expected. Although pyoverdine is considered to be a public good, neither spatial heterogeneity nor heritability provide a meaningful description of the variability. Instead we characterize rapid fluctuations in pyoverdine concentration, and propose a model based on a phenotypic switch in pyoverdine metabolism that is in good agreement with the experimental data.