Dual Symbiosis in a Bathymodiolus sp. Mussel from a Methane Seep on the Gabon Continental Margin (Southeast Atlantic): 16S rRNA Phylogeny and Distribution of the Symbionts in Gills

IFREMER Départment Environnement Profond, Centre de Brest, Plouzané, Germany.
Applied and Environmental Microbiology (Impact Factor: 3.67). 05/2005; 71(4):1694-700. DOI: 10.1128/AEM.71.4.1694-1700.2005
Source: PubMed


Deep-sea mussels of the genus Bathymodiolus (Bivalvia: Mytilidae) harbor symbiotic bacteria in their gills and are among the dominant invertebrate species at cold seeps
and hydrothermal vents. An undescribed Bathymodiolus species was collected at a depth of 3,150 m in a newly discovered cold seep area on the southeast Atlantic margin, close
to the Zaire channel. Transmission electron microscopy, comparative 16S rRNA analysis, and fluorescence in situ hybridization
indicated that this Bathymodiolus sp. lives in a dual symbiosis with sulfide- and methane-oxidizing bacteria. A distinct distribution pattern of the symbiotic
bacteria in the gill epithelium was observed, with the thiotrophic symbiont dominating the apical region and the methanotrophic
symbiont more abundant in the basal region of the bacteriocytes. No variations in this distribution pattern or in the relative
abundances of the two symbionts were observed in mussels collected from three different mussel beds with methane concentrations
ranging from 0.7 to 33.7 μM. The 16S rRNA sequence of the methanotrophic symbiont is most closely related to those of known
methanotrophic symbionts from other bathymodiolid mussels. Surprisingly, the thiotrophic Bathymodiolus sp. 16S rRNA sequence does not fall into the monophyletic group of sequences from thiotrophic symbionts of all other Bathymodiolus hosts. While these mussel species all come from vents, this study describes the first thiotrophic sequence from a seep mussel
and shows that it is most closely related (99% sequence identity) to an environmental clone sequence obtained from a hydrothermal
plume near Japan.

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