1:45 PM - 2:00 PM
[BBC03-01] Chemical speciation analysis of the brown and black precipitates observed in the gill chamber of the vent shrimp Rimicaris kairei
Keywords:hydrothermal vent, Rimicaris kairei, biomineralization, XAFS
Specimens of Rimicaris kairei were collected during the YK16-E02 cruise at two hydrothermal vent site, Edmond and Kairei on the CIR. Each tissues were fixed in 99.5 % ethanol, and embedded in Epoxy resin(Epofix, Struers), and both sides polished thin section with a thickness of about 50 µm were obtained. Thin section was subjected to μ-XRF element analysis and Fe K-edge XANES analysis at KEK PF BL-4A to investigate the element distribution and the speciation of iron around the bacteria. Fitting was carried out using a software REX 2000 (Rigaku) using ferrihydrite, goethite, magnetite, FePO4, pyrite, pyrrhotite as reference materials.
By observing the freeze-dried samples by scanning electron microscope (JSM-6100, JEOL) and thin section samples by polarized microscopy, it was observed that the brown precipitates forms crusts of about 50 μm in thickness and covers entirely the inside of the branchiostegite, where black precipitates occur as submicron size microparticles in organic filmy tissues around filamentous bacteria. From the XANES fitting, it was suggested that the brown precipitates contain ferrihydrite, goethite, FePO4, while the black precipitates contain ferrihydrite, goethite, FePO4, and pyrrhotite. It was revealed that iron exists as Fe3+ in the brown precipitate, but in the black precipitate, iron exist as a mixture of Fe2+ and Fe3+. It is estimated that the brown precipitates were formed in the aerobic environment and the black precipitates were formed in the relatively anaerobic environment. Overall, our suggested that the gill chamber environment was diverse even among the same species. We will perform next-generation sequencing of microbes in the gill chamber, and we need to investigate in detail the precipitation conditions of each mineral and the environment in which the host can grow.