Research theme

Intracellular symbiotic bacteria (endosymbionts) of the weevil Sitophilus highly contribute to the destructive power of this cereal pest, as they complement the host diet with metabolic components lacking in cereal grains (e.g. amino acids and vitamins). As mitochondria, endosymbionts are transmitted maternally (via oocytes) to the offsprings. Early during embryonic development, endosymbionts induce the differentiation of specialized host cells called the bacteriocytes, which group together to form the bacteriome organ in larvae. The bacteriocytes house endosymbionts and protect them against the insect immune response. Bacteria are only tolerated inside these specific cells, and their externalization from the bacteriocytes results in a drastic humoral immune response that sanctions endosymbionts. In adults, endosymbionts are housed within the bactériomes of mesenteric ceca of the midgut. Their number increases dramatically during the first week after adult molting. Remarkably, adults are completely devoid of gut endosymbionts two weeks later, while they keep ovary endosymbionts for transmission to offsprings. This biological phenomenon is being elucidated.

The aim of SymSIm team is to understand the cellular and molecular processes involved in bacteriocyte cell differentiation and to unravel the mechanisms of endosymbiont control and their maintenance throughout host generations. These functional investigations use genomic and integrative approaches in order to decipher the molecular dialogue occurring between bacteria and insects. The team aims to understand how symbiosis is integrated into the insect organization, at the level of the organism (metabolism, physiology), cells (differentiation and organization of bacteriocytes), and molecules (signaling pathways involved, regulation). SymSIm team also intends to unravel how the insect immune system would have evolved to both tolerate and control the presence of bacteria within the host system.

A second field of interest to SymSIm team is to understand the evolutionary bases of intracellular symbiosis within the coleopteran super family Curculionoidea. This work that uses phylogenetic and histological techniques aims at analysing the diversity of intracellular symbiosis within this large super family and to learn about symbiosis impact on insect adaptation and evolution.