|Title||Epsilonproteobacteria as gill epibionts of the hydrothermal vent gastropod Cyathermia naticoides (North East‑Pacific Rise)|
|Publication Type||Journal Article|
|Year of Publication||2014|
|Authors||Zbinden, M, Marqué, L, Gaudron, S, Ravaux, J, Duperron, S|
Molluscs, and particularly gastropods, are one of the major taxonomic groups at vents. In these ecosystems, devoid of light, chemoautotrophic bacteria are at the base of the food web, and symbiotic association between metazoa and these bacteria are numerous. Nevertheless, apart few "large size" well known species, the "small size" gastropods (shell < 5mm), although very abundant, remain poorly studied regarding symbioses. We investigated here Cyathermia naticoides (Warén and Bouchet 1989), a small coiled gastropod found in abundance on the East Pacific Rise among Riftia pachyptila tubes and usually inferred to graze on tubeworms bacterial cover, and/or filter feeding. Among molluscs, symbioses are well known in large species and almost exclusively rely on sulfide or methane-oxidizing Proteobacterial endosymbionts, occurring within the host tissues in gill epithelial bacteriocytes. Combining several approaches (molecular biology, microscopy, stable isotopes analyses), we described here an unusual symbiosis, where autotrophic filamentous Epsilonproteobacteria are located extracellularly, at the base of hosts gill filaments. Numerous endocytotic lysosome-like structures were observed in the gill epithelium of the animal suggesting bacteria may contribute to its nutrition through intracellular digestion by gill cells. Additional food source by non-symbiotic Proteobacteria grazed on R. pachyptila tubes could complete the diet. The possible role of temperature in the selection of Epsilon vs Gamma proteobacterial partners is discussed.