Category: Uncategorized

PhD Defense – Charlotte COMBE – 09/05/2016 @14h – LOV

Title: Quantitative and qualitative effects of light on the growth of microalgae in dense crop and their production of molecules of interest”

Microalgae are a promising source of third generation biofuels. The interest on these photosynthetic microorganisms also lies within the extent of the spectrum of molecules that they can produce, such as proteins, pigments, and vitamins.

Nevertheless, further progress is still necessary to reduce the economic and environmental costs of cultivation processes and to ensure the viability of this sector. In particular, better understanding of the effect of light on the productivity of dense cultures is an essential step to optimize these processes.

The aim of this thesis is to study the quantitative and qualitative effects of light on growth and acclimation mechanisms of two species of microalgae with high biotechnological interest; Dunaliella salina and Tisochrysis lutea.

The first part of this thesis examines the response of Dunaliella salina to rapid light changes, by reproducing irradiance fluctuations typically experienced by microalgal cells in a highly turbid suspension in raceway ponds. In the second part, we analyzed the response of Dunaliella salina and Tisochrysis lutea to different light spectra. Our experimental and theoretical approach allowed us to identify the effect of colored light on productivity and pigment composition of microalgae. Furthermore, our results offer encouraging prospects for elevate understanding and use of light and improve the energy performance of these processes.

Jury members:

Dr. Claude Aflalo – Rapporteur
Pr. Yannick Huot – Rapporteur
Dr. Jean-Paul Cadoret – Examinateur
Dr. Bruno Sialve – Examinateur
Dr. Olivier Bernard – Co-directeur
Dr. Sophie Rabouille – Co-directrice
Dr. Antoine Sciandra – Directeur
Pr. Paul Nival – Président du jury


Dunaliella salina, Tisochrysis lutea, biofuel, photosynthesis, hydrodynamics, flashing light, photolimitation, LED, wavelengths,pigments, phenotypic plasticity, photoacclimation, productivity

PhD defense: Elsa ROUSSEAU – 27/05/16 @ 13h30 salle Euler Violet

Titel: Effect of genetic drift and selection on plant resistance durability to viruses.

Plants can be fully protected from their pathogens when they carry major resistance genes, but the efficiency of these genes is limited by the emergence and spread of adapted, resistance-breaking pathogen variants. This thesis studies how evolutionary forces imposed by the plants on pathogen populations may increase the durability of major resistance genes. Using plant viruses as a biological model, this thesis investigates the effect of genetic drift and selection, from the within-host to the host population level. Firstly, a stochastic epidemiological SI model at the field level showed that genetic drift could be particularly beneficial for crop yield when the fitness cost associated with virus adaptation to resistance was intermediate in susceptible plants. Then, the design and validation of a mechanistic-statistical model based on deterministic Lotka-Volterra equations and stochastic Dirichlet-multinomial processes allowed to disentangle the effects of genetic drift from those of selection on temporal data of within-host competition between virus variants. The intensities of genetic drift and selection acting on virus populations were shown to be controlled genetically by the hosts. Finally, a correlation analysis between these estimations of genetic drift and selection intensities and an experimental estimation of the durability of a major resistance gene showed that strong genetic drift during the early stages of plant infection led to an increase in resistance durability. These results open new perspectives for more durable management of plant resistance, by breeding plant varieties inducing strong genetic drift on pathogen populations

Jury members:

Fernando GARCIA ARENAL, Universidad Politécnica de Madrid


Elisabeta VERGU, INRA

Christian LANNOU, INRA


Alain VIARI, Inria

Jean Luc GOUZE, Inria

Frédéric FABRE, INRA

Keywords: genetic drift, selection, resistance durability, experimental evolution, epidemiology.

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