Phylogenetic characterization of sulfur-oxidizing bacterial endosymbionts in three tropical Lucinidae by 16S rDNA sequence analysis

Nearly complete 16S rDNA sequences were determined for three tropical Lucinid endosymbionts and compared with previously examined symbiotic thioautotrophs. These symbionts include one previously analyzed, Codakia orbicularis, and two new gill symbionts of Lingua pensylvanica and Lucina pectinata. Only one type of bacterial 16S rDNA was detected in the two analyzed specimens of each host species, showing that the symbiont population within a Bivalve species appears to be composed of a single species. The three symbiont sequences analyzed fall within the γ-subdivision of the Proteobacteria, in the cluster containing previously examined symbiotic thioautotrophs from the bivalve superfamily Lucinacea. The two bivalves from shallow-water sea-grass beds, Codakia orbicularis and Lingua pensylvanica, seem to be colonized by the same symbiotic bacteria. However, the symbiont of Lucina pectinata, which that lives in sulfide-rich muddy mangrove areas, seems to be a deeply branching microorganism of the Lucinacea cluster