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Ponnudurai, R, Sayavedra L, Kleiner M, Heiden SE, Thurmer A, Felbeck H, Schluter R, Sievert SM, Daniel R, Schweder T, Markert S.  2017.  Genome sequence of the sulfur-oxidizing Bathymodiolus thermophilus gill endosymbiont. Standards in Genomic Sciences. 12   10.1186/s40793-017-0266-y   AbstractWebsite

Bathymodiolus thermophilus, a mytilid mussel inhabiting the deep-sea hydrothermal vents of the East Pacific Rise, lives in symbiosis with chemosynthetic Gammaproteobacteria within its gills. The intracellular symbiont population synthesizes nutrients for the bivalve host using the reduced sulfur compounds emanating from the vents as energy source. As the symbiont is uncultured, comprehensive and detailed insights into its metabolism and its interactions with the host can only be obtained from culture-independent approaches such as genomics and proteomics. In this study, we report the first draft genome sequence of the sulfur-oxidizing symbiont of B. thermophilus, here tentatively named Candidatus Thioglobus thermophilus. The draft genome (3.1 Mb) harbors 3045 protein-coding genes. It revealed pathways for the use of sulfide and thiosulfate as energy sources and encodes the Calvin-Benson-Bassham cycle for CO2 fixation. Enzymes required for the synthesis of the tricarboxylic acid cycle intermediates oxaloacetate and succinate were absent, suggesting that these intermediates may be substituted by metabolites from external sources. We also detected a repertoire of genes associated with cell surface adhesion, bacteriotoxicity and phage immunity, which may perform symbiosis-specific roles in the B. thermophilus symbiosis.

Duplessis, MR, Dufour SC, Blankenship LE, Felbeck H, Yayanos AA.  2004.  Anatomical and experimental evidence for particulate feeding in Lucinoma aequizonata and Parvilucina tenuisculpta (Bivalvia : Lucinidae) from the Santa Barbara Basin. Marine Biology. 145:551-561.   10.1007/s00227-004-1350-6   AbstractWebsite

Previous nutritional models for adults of the lucinid bivalve Lucinoma aequizonata contend that symbiotic chemoautotrophic bacteria provide most of the organic carbon for the host. The existence of this symbiosis, coupled with the host's distinctive anatomical features, shaped the impression that particulate feeding was not a significant part of L. aequizonata nutrition. Here, we use several techniques to show that particulate feeding is a consistent and important part of the L. aequizonata nutritional strategy. Histological and scanning electron microscopy observations reveal that the gills of L. aequizonata, like those of the lucinid Parvilucina tenuisculpta, have functional mucociliary epithelia, able to transport captured particles to the mouth. Observations of gut content and radiolabeled feeding experiments indicate that L. aequizonata does ingest and assimilate carbon from particulate organic matter. Furthermore, molecular identification of a broad spectrum of organisms in the guts of native adult specimens demonstrates that L. aequizonata is non-selective when ingesting organic material, and has a mixotrophic diet.

Boetius, A, Felbeck H.  1995.  Digestive enzymes in marine invertebrates from hydrothermal vents and other reducing environments. Marine Biology. 122:105-113.   10.1007/bf00349283   AbstractWebsite

The present study demonstrates the potential hydrolytic activities in the symbiont-containing tissues of the vent invertebrates Riftia pachyptila, Bathymodiolus thermophilus (collected in 1991 at the East Pacific Rise) and the shallow-water bivalve Lucinoma aequizonata (collected in 1991 from the Santa Barbara Basin). Activities of phosphatases, esterases, beta-glucuronidase and leucine aminopeptidase were comparable to those of digestive tract tissues of other marine invertebrates. A lack in most glycosidases as well as in trypsin and chymotrypsin was observed. Activities of lysozyme and chitobiase were rather high. In all vent invertebrates with symbionts and in L. aequizonata, the symbiont-containing tissues and the symbiont-free tissues had similar levels of enzymatic activities, indicating that polymeric nutrients could be hydrolysed after release from the symbionts and cellular uptake. The high activities of alpha-fucosidase in all vent invertebrates as well as in the shallow-water bivalve L. aequizonata could point to the existence of a yet undescribed substrate available to hydrolysation. The ectosymbionts-carrying polychaete Alvinella pompejana (collected in 1991 at the East Pacific Rise, EPR) shows high lysozyme activities in its gut, consistent with the proposed food source of bacteria. For the vent crab Bythogrea thermydron (also collected in 1991 at the EPR) hydrolytic activities were highest in the gut, dominated by esterase and peptidase activities which support their proposed carnivorous food source. A snail and a limpet collected from R. pachyptila tubes showed high levels of chitobiase suggesting a food source of grazed bacteria or ingested R. pachyptila tube.