A tale of two symbioses: molecular mechanisms underlying insect-microbe associations

Aurélien Vigneron

Amphitheatre Guyton de Morveau, 11 AM

Insects are efficacious model systems for studying how interactions with microbial partners -both parasites or mutualists- impact host fitness and contribute to the host evolution. A major challenge in this research field is to identify the factors structuring the development of the host’s immune system in the perpetual tug-of-war between a parasite and its partner. A second central goal is the understanding of trade-offs associated with mutualism, which drives the evolution of insects. Using two models, the Tsetse flies (Glossina spp.) and the cereal weevils (Sitophilus spp.), I addressed those two questions through the investigation of the microbe-derived factors and mechanisms impacting the host biology, and subsequently the host-associated pathways that respond to these factors.

Tsetse flies (Glossina spp.) are the main vector of the African trypanosomes, which are the causative agents of human and animal trypanosomiases. Trypanosomes that colonize tsetse’s midgut must pass through the fly’s cardia organ and reach the salivary glands in order to transmit to a new vertebrate host. However, some flies with midgut infection never develop a salivary glands infection – the reasons for which are unclear. Using large-scale transcriptomics, microscopy and functional genomics, I deciphered the factors that regulate trypanosome migration through tsetse’s cardia, thus determining the ability of the fly to transmit the parasite.

Cereal weevils Sitophilus spp. are associated with the mutualist endosymbiont Sodalis pierantonius, which supports its host by providing vitamins and amino acids that foster cuticle synthesis. However, the endosymbiont is dislodged from the adult weevils’ gut soon after its ultimate molting. Using microscopy, manipulation of the insect diet and amino acids quantification, I uncovered fine-tuned apoptotic and autophagic processes that govern endosymbionts elimination immediately after the insect cuticle synthesis is achieved. My results provide evidence of a coordinated molecular cross-talk between metabolic and cellular processes that drives tolerance or recycling of endosymbionts depending on the host’s needs.

These two examples show that host-microbe interactions, independently of their nature, have in common the intimate molecular dialogue that is ongoing between the partners to regulate and perpetuate symbioses.

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A tale of two symbioses: molecular mechanisms underlying insect-microbe associations

Aurélien Vigneron

Amphitheatre Guyton de Morveau, 11 AM

 

Insects are efficacious model systems for studying how interactions with microbial partners -both parasites or mutualists- impact host fitness and contribute to the host evolution. A major challenge in this research field is to identify the factors structuring the development of the host's immune system in the perpetual tug-of-war between a parasite and its partner. A second central goal is the understanding of trade-offs associated with mutualism, which drives the evolution of insects. Using two models, the Tsetse flies (Glossina spp.) and the cereal weevils (Sitophilus spp.), I addressed those two questions through the investigation of the microbe-derived factors and mechanisms impacting the host biology, and subsequently the host-associated pathways that respond to these factors.

Tsetse flies (Glossina spp.) are the main vector of the African trypanosomes, which are the causative agents of human and animal trypanosomiases. Trypanosomes that colonize tsetse’s midgut must pass through the fly’s cardia organ and reach the salivary glands in order to transmit to a new vertebrate host. However, some flies with midgut infection never develop a salivary glands infection – the reasons for which are unclear. Using large-scale transcriptomics, microscopy and functional genomics, I deciphered the factors that regulate trypanosome migration through tsetse’s cardia, thus determining the ability of the fly to transmit the parasite.

Cereal weevils Sitophilus spp. are associated with the mutualist endosymbiont Sodalis pierantonius, which supports its host by providing vitamins and amino acids that foster cuticle synthesis. However, the endosymbiont is dislodged from the adult weevils' gut soon after its ultimate molting. Using microscopy, manipulation of the insect diet and amino acids quantification, I uncovered fine-tuned apoptotic and autophagic processes that govern endosymbionts elimination immediately after the insect cuticle synthesis is achieved. My results provide evidence of a coordinated molecular cross-talk between metabolic and cellular processes that drives tolerance or recycling of endosymbionts depending on the host’s needs.

These two examples show that host-microbe interactions, independently of their nature, have in common the intimate molecular dialogue that is ongoing between the partners to regulate and perpetuate symbioses.

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