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Interactions entre ciliés et métazoaires dans deux environnements marins contrastés : les sources hydrothermales et les sédiments anoxiques

Abstract : Cilliates (Ciliophora) are defined as one of the main groups within the eukaryotic systematic. These ubiquitous unicellular microorganisms have adapted to a wide range of habitats (terrestrial, marine and freshwater habitats) using different morphological and physiological strategies, some of which are based on symbiosis. Out of the numerous ecological niches found in the marine environment, two were selected in this study : hydrothermal vents and coastal marine sediments. Morphological observations (live, stained, scanning, and transmission electron microscopy) and molecular genetic analyses (PCR, cloning, sequencing, in situ hybridization) were combined in order to characterise the unicellular eukaryote communities associated with endemic metazoans from these two contrasted environments (hydrothermal bivalves and intertidal polychaetes). The present study (i) compared the distribution of unicellular eukaryotes associated with different deep-sea marine environments (seawater, hydrothermal vents, Bathymodiolus), (ii) revealed new clades within the ciliates detected in hydrothermal bivalves, (iii) redescribed and compared the distribution of astomes, a specific group of ciliates, only found associated with metazoans, (iv) defined endocytoplasmic bacteria as a third partner in this tripartite association. Here we show that a majority of unicellular eukaryotes detected in hydrothermal environments are also widespread in oceanic waters. However, distinct and stable ecological niches, such as endemic bivalves, harbour more specific ciliate communities, either symbiotic and/or parasitic. Moreover, Cirratulidae polychaetes from anoxic coastal sediments are part of a tripartite association with endocommensal ciliates harbouring endocytoplasmic bacteria. The endosymbiotic bacteria, mainly affiliated to Epsilon-Proteobacteria and to a new Proteobacteria clade named Durchoniella Endocytoplasmic Proteobacteria Group (DEPG), were phylogeneticaly distant from any previously described Proteobacteria, suggesting a common evolutionary history. These new models may help to better understand the interactions between eukaryotes and bacteria.
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  • HAL Id : tel-01146192, version 1


Anne-Laure Sauvadet. Interactions entre ciliés et métazoaires dans deux environnements marins contrastés : les sources hydrothermales et les sédiments anoxiques. Ecosystèmes. Paris 6, 2010. Français. ⟨NNT : 2010PA066521⟩. ⟨tel-01146192⟩



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