BackgroundMutualistic symbioses between invertebrate animals and chemosynthetic bacteria are at the basis of Life in hydrothermal vent ecosystems. The shrimp Rimicaris exoculata, which dominates animal fauna along the Mid Atlantic Ridge, houses in its cephalothorax a complex bacterial community including Campylobacteria, Gamma- Delta- and some recently discovered iron oxyhydroxides-coated Zetaproteobacteria. This epibiotic consortium uses iron, sulfide, methane and hydrogen as energy sources. Here, we used a DNA extraction procedure adapted to recalcitrant embedded bacteria and generated shotgun metagenomes from Rimicaris exoculata cephalothoracic epibiotic community. We aimed reconstructing symbiotic genomes from specimen collected in three geochemically contrasted vent fields, TAG, Rainbow and Snake Pit to unravel the specificity, variability and adaptation of host-microbes associations.ResultsUsing these data we were able to reconstruct 49 high quality metagenome-assembled genomes (MAGs) from TAG and Rainbow vents fields. Most critically, two MAGs in our collection were affiliated to Zetaproteobacteria and had no close relatives (ANI < 77% from the closest relative Ghiorsea bivora isolated from TAG and <88% between each other), suggesting potential novel species. Genes for CBB carbon fixation, iron and sulfur oxidation, as well as nitrate reduction, occurred in both MAGs. However, genes for hydrogen oxidation and quorum sensing as well as multicopper oxidases occurred in one MAG only, suggesting shared and specific potential functions for these two novel Zetaproteobacteria symbiotic lineages. Overall, we observed highly similar symbionts that co-exist in a single shrimp at both basaltic TAG and ultramafic Rainbow vent sites. Nevertheless, further insights into the seemingly functional redundancy between those epibionts revealed important differences. ConclusionThese data highlight microniche partitioning in the Rimicaris holobiont and confirm recent works that show functional diversity enables multiple symbiont strains to coexist in animals from hydrothermal vents.