Intra- and inter-population diversity of the Gammaproteobacteria Endorifita persephone in vestimentiferan tubeworms from the eastern Pacific.




Perez, Maëva

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Vestimentiferan tubeworms of the eastern Pacific Ocean are often keystone species in vent communities. These polychaetes are host to intracellular Gammaproteobacteria symbionts. In this association, the siboglinid worms supply their symbionts with the compounds necessary to chemosynthesis while the sulfide oxidizing bacteria provide their host with the organic molecules necessary for their metabolism. The adult worms lack a digestive system and are therefore completely dependent on their symbionts for their nutrition. Given the obligate nature of the association for the host, it is surprising that the symbionts are not transmitted from parents to offspring but are acquired de novo from the environment at each generation. In other known cases of horizontally acquired mutualism (e.g. Rhizobium-legumes, dinoflagellates- corals), obtaining symbionts from the environment benefit the hosts by allowing for a degree of partner choice. According to the partner choice hypothesis, tubeworms that associate with the best-adapted partner(s) to a specific range of habitat conditions are in turn better adapted to this environment. Of course, this hypothesis assumes that there is diversity within the symbiotic partners. Phylogenetic analyses on the other hand seemed to indicate that nearly all species of vent tubeworms of the eastern Pacific were associated with the same species of symbionts: Candidatus Endoriftia persephone. However, these studies focussed on a few molecular markers. In this thesis, I used in situ hybridization and next generation sequencing to characterize the symbiont diversity at the species and strain level, as well as within individual hosts and across host species. I found that the intra-host symbiont populations are likely composed of multiple strains or lineages of the same bacterial species, that the symbiont populations separated by mid-ocean ridge discontinuities are vicariant, and that other factors such as local environmental conditions or host specificity might participate in shaping the genetic make-up of these populations.



genome, bacteria, symbiosis, diversity, evolution, hydrothermal vents, vestimentiferan, Endeavour, tubeworm, population, FISH, CRISPR