Iron oxide deposits associated with the ectosymbiotic bacteria in the hydrothermal vent shrimp Rimicaris exoculata
- 1Université de Liège, Laboratoire de Morphologie fonctionnelle et Evolutive, Unité de Morphologie ultrastructurale et Cellule d'Appui Technologique en Microscopie (Catμ), allée de la chimie, 3, 4000 Liège, Belgium
- 2Laboratoire de Microbiologie et Biotechnologie des Extrêmophiles, Ifremer, centre de Brest, BP 70, 29280 Plouzané, France
- 3Department of Chemistry, Missouri University of Science and Technology, University of Missouri-Rolla, Rolla, Missouri 65409-0010, USA
- 4Department of Physics, B5, University of Liège, 4000 Sart-Tilman, Belgium
- 5UMR CNRS 7138 "Systématique, Adaptation et Evolution", Université Pierre et Marie Curie, 7 Quai St Bernard, Bâtiment A, 75252 Paris Cedex 05, France
Abstract. The Rimicaris exoculata shrimp is considered as a primary consumer that dominates the fauna of most Mid-Atlantic Ridge (MAR) hydrothermal ecosystems. These shrimps harbour in their gill chambers an important ectosymbiotic community of chemoautotrophic bacteria associated with iron oxide deposits. The structure and elemental composition of the mineral concretions associated with these bacteria have been investigated by using LM, ESEM, TEM STEM and EDX microanalyses. The nature of the iron oxides in shrimps obtained from the Rainbow vent field has also been determined by Mössbauer spectroscopy. This multidisciplinary approach has revealed that the three layers of mineral crust in the Rimicaris exoculata shrimps consist of large concretions formed by aggregated nanoparticles of two-line ferrihydrite and include other minor elements as Si, Ca, Mg, S and P, probably present as silicates cations, sulphates or phosphates respectively that may contribute to stabilise the ferrihydrite form of iron oxides. TEM-observations on the bacteria have revealed their close interactions with these minerals. Abiotic and biotic precipitation could occur within the gill chamber of Rimicaris exoculata, suggesting the biologically-mediated formation of the iron oxide deposits. The difference of the bacterial density in the three-mineral crust layers could be correlated to the importance of the iron oxide concretions and suggest that the first mineral particles precipitates on the lower layer which could be considered as the most likely location of iron-oxidizing bacteria.