Frédéric CHEVALIER

PhD, University of Poitiers (France), 2011.

MS “Fonctional Ecology : from molecules to natural populations”, University of Perpignan Via Domitia, 2007

PhD Thesis:
Wolbachia (α-proteobacteria) symbiosis: impacts on the immune system and the immunocompetence of its host Armadillidium vulgare (crustacean isopod)

  • Supervisors: PR. Pierre GREVE and DR. Christine BRAQUART-VARNIER

Summary

Symbiosis represents a major evolutionary force leading to many adaptations of the partners, especially in response to pathogens. The endosymbiotic bacteria Wolbachia (α-proteobacteria) confer resistance to pathogens for vector insects. In the isopod crustacean Armadillidium vulgare, Wolbachia modify the host immunocompetence by decreasing total hemocyte count (THC) and increasing the natural septicemia. The presence of the bacteria in hemocytes and hematopoietic organs raises many questions about consequences of this presence on immune system functions and on immunocompetence of A. vulgare.
We thus studied the impact of the symbiosis on hemocytes, immunocompetence and immune gene expressions. We showed by fluorescent in situ hybridization that Wolbachia infect more than one third of the hemocytes and by flow cytometry that the proportion of circulating granular hemocytes is lower in one-year old infected animals, without any difference in THC at this age. Phenoloxidase activity decreases with age and symbiotic status. However, the Wolbachia presence seems to protect hemocytes against apoptosis and to increase host immunocompetence during infection with Listeria ivanovii. Finally, the quantification of the expression of immune genes, identified after establishing the first reference transcriptome of isopods (ANR EndoSymbArt project), revealed a trend to under-expression in whole animal and ovaries but an over-expression in immune tissues.
Therefore, the Wolbachia presence modifies immune system characteristics at cellular and humoral levels and the immunocompetence of A. vulgare. The study of new parameters will clarify if the Wolbachia presence is a real benefit to its host or if the bacteria do have a significant cost to its host.

Keywords : Armadillidium vulgare, Wolbachia, immunity, hemocytes, hematopoietic organs, PO activity, total hemocytes count, flow cytometry, RT-qPCR.

Teaching

  • 2007-2010 : Teaching Tutor at University of Poitiers (246 Contact Hours from B.S. level to M.S. level)
  • 2010-2011 : Education and Research Assistant at University of Poitiers (296 Contact Hours from B.S. level to M.S. level)

Selected publications

  • Feminizing Wolbachia: A transcriptomics approach with insights on the immune response genes in Armadillidium vulgare. Frédéric Chevalier, Juline Herbinière-Gaboreau, Delphine Charif, Guillaume Mitta, Frédéric Gavory, Patrick Wincker, Pierre Grève, Christine Braquart-Varnier, Didier Bouchon. BMC Microbiology 2012 12:suppl S1.
  • Armadillidium vulgareWolbachia association: Impacts on host immune system and immunocompetence. Frédéric Chevalier, Mathieu Sicard, Joanne Bertaux, Juline Herbinière, Franck Morel, Didier Bouchon, Pierre Grève & Christine Braquart-Varnier. Proceedings of the 8th International Symposium of Terrestrial Isopod Biology 2008.
  • The first reference transcriptome in isopods. Frédéric Chevalier, Juline Herbinière-Gaboreau, Delphine Charif, Guillaume Mitta, Frédéric Gavory, Patrick Wincker, Pierre Grève, Christine Braquart-Varnier, Didier Bouchon. Proceedings of the 8th International Symposium of Terrestrial Isopod Biology 2008.
  • The immune cellular effectors of terrestrial isopod Armadillidium vulgare: Meeting with their invaders, Wolbachia. Frédéric Chevalier, Juline Herbinière-Gaboreau, Joanne Bertaux, Maryline Raimond, Franck Morel, Didier Bouchon, Pierre Grève & Christine Braquart-Varnier. PLoS One 2011 6(4):e18531.
  • Variations of immune parameters in terrestrial isopods: a matter of Gender, Aging and Wolbachia. Mathieu Sicard, Frédéric Chevalier, Mickaël De Vlechouver, Didier Bouchon, Pierre Grève & Christine Braquart-Varnier. Naturwissenschaften 2010 97(9):819-826.

Coordonnées

Email : frederic.d.chevalier@gmail.com

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