Bacterial host specificity of Lucinacea endosymbionts: interspecific variation in 16S rRNA sequences.

Three tropical lucinid clams (Codakia orbiculata, Codakia pectinella and Lucina nassula) from a shallow coastal environment have been studied regarding to their thioautotrophic bacterial endosymbionts. The 16S rRNA genes (rDNA) from these three endosymbionts were amplified using PCR. Phylogenetic analysis by distance matrix and parsimony methods always placed the newly examined symbionts within the monophyletic group composed of symbionts of the bivalve superfamily Lucinacea. A same single 16S rRNA sequence was found in C. orbiculata and C. pectinella and was identical to that found in C. orbicularis and Linga pensylvanica, two other lucinids living in the same type of environment. These data indicate that a same symbiont species may be associated with different host species. Lucina nassula host a symbiont with a distinct 16S rDNA sequence, but very closely related to the former.