New insigths on the metabolic diversity

18 The shrimp Rimicaris exoculata (Williams and Rona, 1986) dominates the megafauna of 19 some of the Mid Atlantic ridge hydrothermal vent sites. This species harbors a rich 20 community of bacterial epibionts inside its gill chamber. Literature data indicate that a single 21 16S rRNA phylotype dominates this epibiotic community, and is assumed to be a sulfide22 oxidizing bacteria. However attempts of cultivation were not successful and did not allow to 23 confirm it. The aim of our study was to test the hypothesis of sulfide oxidation in the gill 24 chamber, by a multidisciplinary approach, using in vivo experiments at in situ pressure in the 25 presence of sulfide, microscopic observations and a molecular survey. Morphology of 26 microorganisms, before and after treatment, was analyzed to test the effect of sulfide 27 depletion and re-exposure. Our observations, as well as molecular data indicate a wider 28 diversity than previously described for this shrimp’s epibiotic community. We observed 29 occurrence of bacterial intracellular sulfurand iron-enriched granules and some 30 methanotrophic-like bacteria cells for the first time. Genes that are characteristic of methane31 oxidizing (pmoA) and sulfide-oxidizing (APS) bacteria were identified. These results suggest 32 that three metabolic types (iron, sulfide and methane oxidation) may co-occur within the 33 epibiont community associated with Rimicaris exoculata. As this shrimp colonizes chemically 34 contrasted environments, the relative abundance of each metabolic type could vary according 35 to the local availability of reduced compounds. 36 37