Investigating the lipid profile of animal-microbe symbioses

Lipids are important and understudied elements of host-bacteria interactions. Lipids play central roles in defining cellular membranes, they have a structural role but also influence the distribution and activity of transporters, enzymes and receptors. Aside of their functions in the membrane, they have important functions as signaling molecules, energy storages, coenzymes or toxins. In pathogenic interactions, lipids have been shown to participate to every stage of the interaction between the host and the bacteria. A few studies have focused on beneficial symbioses and we only start to discover the importance of lipids in those interactions. Much of the functional importance of the rich chemical diversity of lipids remains unknown. In this study, I aimed to describe the chemical landscape of deep-sea mussels living in close association with chemoautotrophic bacteria (Chapter I) and determine the identity, distribution and potential functions of a metabolite group specific to the association between deep-sea mussels and methane-oxidizing symbionts (Chapter II). This research was expanded to shallow water symbioses formed by gutless annelids and chemoautotrophic bacteria. The study of their sterol pool revealed a new phytosterol synthesis pathway specific to animals (Chapter III).