Ultrastructural and molecular evidence for potentially symbiotic bacteria within the byssal plaques of the deep-sea hydrothermal vent mussel Bathymodiolus azoricus
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This study reports on the presence of a putatively symbiotic bacterial flora within the byssus plaque of the deep sea hydrothermal mussel Bathymodiolus azoricus, contributing to metal sequestration/deposition and testing positive to methane oxidizing symbiont-specific fluorescent probes. Combining an array of approaches including histology, electron microscopy, X-ray microanalysis, analytical chemistry, and microbiology we provide evidence for the frequently assumed, but rarely shown influence of prokaryotes on the biogeochemical cycling of metals as well as inorganic C sources (i.e., methane) at deep sea hydrothermal vents. Our results indicate that in spite of its antibacterial protective sheath, the byssus plaque gives access to a whole range of prokaryotic organisms which may be responsible for the extremely high concentration of metallic elements (Fe, Cu, Zn, Mn, Co, Mo, Cd, Pb and Hg) measured in this attachment organ. The very high levels of metals in byssus, together with its frequent renewal rate due to the dynamic nature of the habitat, suggest that intra-byssal bacteria may have a major influence on biomineralisation/deposition of metals. The presence of a methanotroph morphotype within the byssus plaque was confirmed by FISH and TEM. The implications of the biogeochemical cycling of metals and methane at hydrothermal vents are discussed.
KeywordsHydrothermal vent Bathymodiolus azoricus Biomineralisation Byssus Endosymbiont Fe-oxidising bacteria
This study was undertaken under the framework of SEAHMA (PDCTM/P/MAR/15281/1999) and FISIOVENT-Physiological adaptations to extreme conditions at deep sea hydrothermal vents, project (POCTI/MAR/55547/2004) funded by FCT, Portugal. The Pluriannual and Programatic funding schemes of FCT-MCTES and DRCT-Azores to the R&D Unit #531 are acknowledged. Postdoctoral fellowship was awarded to Eniko Kadar (SFRH-BPD-19625/2004) and to Raul Bettencourt (SFRH/BPD/14896/2004) by FCT. We thank the crew of R/V Atalante, the ROV team and the crew of R/V Arquipelago for technical assistance during sample collection. Domitilia Rosa is acknowledged for her assistance in the histological preparations.
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