Sulfur-oxidizing endosymbiosis in <i>Divaricella quadrisulcata</i> (Bivalvia : Lucinidae): Morphological, ultrastructural, and phylogenetic analysis

Gros, O, Frenkiel L, Felbeck H.  2000.  Sulfur-oxidizing endosymbiosis in Divaricella quadrisulcata (Bivalvia : Lucinidae): Morphological, ultrastructural, and phylogenetic analysis. Symbiosis. 29:293-317.


16S rRNA gene, bacteria, bacterial endosymbionts, chemoautotrophic symbionts, codakia-orbicularis bivalvia, environmental, gill ultrastructure, hosts, lucinidae, phylogeny, riftia-pachyptila, symbiosis, symbiotic, transmission, tropical lucinid, vertical transmission


Based on light and electron microscopy, the cellular organization of the gill filament of Divaricella quadrisulcata is described and compared with other gill filaments of lucinids examined to date. TEM observations revealed a dense population of Gram-negative bacteria located within bacteriocytes in the lateral zone of the gill filament which looks similar to that of Codakia orbicularis with typical "granule cells". The digestive tract of this shallow-water lucinid species is less modified than in other lucinid species. The stomach has a well developed gastric shield, a cristalline style protruding in the stomach from a typical style sac, and active digestive diverticula. The mid gut is coiled through the visceral mass. Therefore, D. quadrisulcata appears to be at least partially dependent on filter-feeding for nutrition. Only one type of bacterial 16S rRNA gene was FCR-amplified from symbiont-containing gill tissue of two specimens, indicating a symbiont population composed of a single species. Phylogenetic analysis showed that sequences of D. quadrisulcata- and C. orbicularis-symbiont were 100% identical at all nucleotide positions determined, suggesting that this other tropical lucinid species harbors the same bacterial symbiont species as the previously analyzed C. orbicularis. Thus, D. quadrisulcata appears as the fifth tropical bivalve colonized by the same symbiont species even though it lives in a different habitat as the four other ones. The symbiont transmission mode was investigated by PCR amplifications from mature ovaries and testes. The C. orbicularis-specific 16S rDNA primer set was unsuccesful in amplifying DNA target for all individuals investigated suggesting that the gill-endosymbionts are environmentally transmitted to the new host generation as for all lucinids examined to date.