Approches culturales et moléculaires des assemblages microbiens associés aux polychètes hydrothermaux de la famille Alvinellidae

Cultural and molecular approaches were used to analyse the microbial assemblages associated to the deep-sea hydrothermal vent polychaete worms of the family Alvinellidae. In a first part of the work, the populations associated to three alvinellid species from the Juan de Fuca Ridge (Paralvinella palmiformis, Paralvinella pandorae and Paralvinella sulfincola) were identified by phylogenetic analyses. A wide microbial diversity was detected, like a great number of new sequences or of sequences belonging to species previously unidentified at deep-sea hydrothermal vents. All the libraries were found to be dominated by sequences affiliated to the epsilon-Proteobacteria. In other respects, fermentative micro-organisms belonging to the Thermococcales, the Thermotogales, the CFB and the Firmicutes were isolated. Autotrophic bacteria reducing sulphur and/or nitrates and belonging to the epsilon-Proteobacteria or to the genus Desulfurobacterium were isolated. Three micro-organisms have been characterised : Caminicella sporogenes, Desulfurobacterium crinifex and Caminibacter hydrogeniphilus. In a last part of the work, ultrastructural and chemical analyses of the atypical macrofilaments formed in culture by Desulfurobacterium crinifex were performed. Finally, in situ colonisation experiments of new surfaces were performed in alvinellid habitat. The microbial cohort preceding the Alvinella spp. settlement and the populations associated to these polychaetes were analysed using cultural and phylogenetic approaches. Thermal and chemical conditions were monitored during the colonisation process. Based on our results, it would seem that the formation of a microbial mat would be necessary to the alvinellid settlement.