MEPS 208:147-155 (2000)  -  doi:10.3354/meps208147

Phylogenetic characterization of endosymbionts in three hydrothermal vent mussels: influence on host distributions

Yoshihiro Fujiwara1,*, Ken Takai2, Katsuyuki Uematsu3, Shinji Tsuchida1, James C. Hunt1, Jun Hashimoto1

1Marine Ecosystems Research Department, Japan Marine Science and Technology Center (JAMSTEC), 2-15 Natsushima, Yokosuka 237-0061, Japan
2Frontier Research Program for Deep-Sea Environment, Japan Marine Science and Technology Center (JAMSTEC), 2-15 Natsushima, Yokosuka 237-0061, Japan
3Marine Work Japan Co., 2-15 Natsushima, Yokosuka 237-0061, Japan

ABSTRACT: The bacterial endosymbionts of 3 hydrothermal vent mussels from Japanese waters were characterized by transmission electron microscopic (TEM) observation and phylogenetic analyses of 16S ribosomal RNA gene sequences. Endosymbionts of Bathymodiolus septemdierum were related to sulfur-oxidizing bacteria (thioautotrophs), while endosymbionts of B. platifrons and B. japonicus were related to methane-oxidizing bacteria (methanotrophs). This is the first report of deep-sea mussels containing only methanotrophs (lacking thioautotrophs) from hydrothermal vents. Comparison of methane and hydrogen sulfide concentrations in end-member fluids from deep-sea hydrothermal vents indicated that methane concentrations were much higher in habitats containing Bathymodiolus spp. which harbored only methanotrophs than in other habitats of hydrothermal vent mussels. The known distribution of other mussels containing only methanotrophs has thus far been limited to cold-seep environments with high methane concentrations from the interstitial water. These results suggest that the distribution of methanotrophic symbioses between deep-sea mussels and methanotrophs is strongly influenced by the methane or hydrocarbon concentrations provided from hydrothermal vent and cold-seep activities (or that methane concentration is a possible limiting factor that restricts the distribution of methanotrophy-dependent symbioses in the deep sea).

KEY WORDS: Methanotrophic symbiosis · Bathymodiolus · Phylogenetic analysis · Host distribution· Methane concentration · Hydrothermal vent

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