Iron oxide deposits associated with the ectosymbiotic bacteria in the hydrothermal vent shrimp &amp;lt;i&amp;gt;Rimicaris exoculata&amp;lt;/i&amp;gt;

L Corbari,M Zbinden,P Compère,G J Long,M.-A Cambon-Bonavita,F Gaill,F Grandjean

doi:10.5194/bg-5-1295-2008

Abstract

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.

Highlights

Rimicaris exoculata (Williams and Rona, 1986) is one of the most dominant species found at the Mid-Atlantic Ridge (MAR) hydrothermal vents
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
Transmission Electron Microscopy (TEM) images (Fig. 2b) reveal that the lower level is characterised by a high density of rod-shaped bacteria; mineral precipitation occurs on the cell walls of these bacteria (Fig. 3a)

Summary

Introduction

Rimicaris exoculata (Williams and Rona, 1986) is one of the most dominant species found at the Mid-Atlantic Ridge (MAR) hydrothermal vents. This endemic shrimp swarms on the chimney walls, exhibiting a patch-like distribution of up to several thousand per square meter (Segonzac et al, 1993). The bacterial community housed in the gill chamber of R. exoculata has been identified as chemoautotrophic bacteria (Wirsen et al, 1993) and phylogenetic analysis revealed that the bacteria could correspond to a single epsilon-proteobacteria phylotype (Polz and Cavanaugh, 1995). Some authors have hypothesized that the bacteria could acquire their energy from sulphide oxidation

Objectives

Methods

Results

Discussion

Conclusion