Alvinella pompejana is a polychaetous annelid that inhabits active deep-sea hydrothermal vent sites along the East Pacific Rise, where it colonizes the walls of actively venting high-temperature chimneys. An abundant, morphologically diverse epibiotic microflora is associated with the worm's dorsal integument, with a highly integrated filamentous morphotype clearly dominating the microbial biomass. It has been suggested that this bacterial population participates in either the nutrition of the worm or in detoxification of the worm's immediate environment. The primary goal of this study was to phylogenetically characterize selected epibionts through the analysis of 16S rRNA gene sequences. Nucleic acids were extracted from bacteria collected from the dorsal surface of A. pompejana. 16S rRNA genes were amplified with universal bacterial primers by the PCR. These genes were subsequently cloned, and the resulting clone library was screened by restriction fragment length polymorphism analysis to identify distinct clone types. The restriction fragment length polymorphism analysis identified 32 different clone families in the library. Four of these families were clearly dominant, representing more than 65% of the library. Representatives from the four most abundant clone families were chosen for complete 16S rRNA gene sequencing and phylogenetic analysis. These gene sequences were analyzed by a variety of phylogenetic inference methods and found to be related to the newly established epsilon subdivision of the division Proteobacteria. Secondary structural model comparisons and comparisons of established signature base positions in the 16S rRNA confirmed the placement of the Alvinella clones in the epsilon subdivision of the Proteobacteria.

Codakia orbicularis is a large tropical member of the bivalve mollusk family Lucinidae which inhabits shallow-water sea-grass beds (Thalassia testudinum environment) and harbors sulfur-oxidizing endosymbiotic bacteria within bacteriocytes of its gill filaments. When a C. orbicularis-specific 16S rDNA (DNA encoding rRNA) primer is used with a bacterium-specific 16S rDNA reverse primer in amplifications by PCR, the primer set was unsuccessful in amplifying symbiont DNA targets from ovaries, eggs, veligers, and metamorphosed juveniles (600 m to 1 mm in shell length) cultivated in sterile sand, whereas successful amplifications were obtained from gill tissue of adult specimens and from metamorphosed juveniles (600 m to 1 mm in shell length) cultivated in unsterilized sea-grass bed sand. To ascertain the presence of the symbiont target in juveniles, restriction fragment length polymorphism analysis, 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 bed sand showed that the sulfur-oxidizing endosymbionts of C. orbicularis are environmentally transmitted to the new generation after larval metamorphosis.

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Abstract. Specimens of alvinellid polychaetes (Alvinella pompejana Desbruy6res andLaubier, 1980 and A. caudata Desbruy6res andLaubier, 1986) and their tubes were sampled from deep-sea hydrothermal vents at 13°N from the manned submersible "Nautile" during the "Hydronaut" cruise (October to November 1987) on the East Pacific Rise. Samples were subjected to bacterial analysis aboard the mother ship "Nadir" to detect bacteria involved in the nitrogen and sulphur cycles, in non-specific heterotrophic processes, and displaying resistance to selected heavy metals. Cultures were incubated at different temperatures under atmospheric and "in situ" (250 atm) pressures. Bacterial growth was observed in enrichment cultures for most metabolic types screened. Heavy-metalresistant bacteria were also detected in many samples. No filamentous bacterial form was observed in the cultures. The results demonstrate a high metabolic diversity in episymbiotic flora, indicating that the worm (A. pompejana or A. caudata), its tube and its epiflora represent a complex micro-ecosystem.