ENVIRONMENTAL TRANSMISSION OF A SULFUR-OXIDIZING BACTERIAL GILL ENDOSYMBIONT IN THE TROPICAL LUCINID BIVALVE CODAKIA-ORBICULARIS

Codakia orbicularis is a large tropical member of the bivalve mollusk family Lucinidae which inhabits shallow-water sea-grass beds (Thalassi a testudinum environment) and harbors sulfur-oxidizing endosymbiotic b acteria within bacteriocytes of its gill filaments, When a C, orbicula ris-specific 16S rDNA (DNA encoding rRNA) primer is used with a bacter ium-specific 16S rDNA reverse primer in amplifications by PCR, the pri mer set was unsuccessful in amplifying symbiont DNA targets from ovari es, eggs, veligers, and metamorphosed juveniles (600 mu m to 1 mm in s hell length) cultivated in sterile sand, whereas successful amplificat ions were obtained from gill tissue of adult specimens and from metamo rphosed juveniles (600 mu m to 1 mm in shell length) cultivated in uns terilized sea-grass bed sand, To ascertain the presence of the symbion t target in juveniles, restriction fragment length polymorphism analys is, Southern blotting, and transmission electron microscopy were used, Specific hybridizations and observation of endosymbiotic bacteria in the gills of numerous juveniles cultivated in unsterilized sea-grass b ed sand showed that the sulfur-oxidizing endosymbionts of C, orbicular is are environmentally transmitted to the new generation after larval metamorphosis.