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Anderson, AE, Felbeck H, Childress JJ.  1990.  Aerobic metabolism is maintained in animal tissue during rapid sulfide oxidation in the symbiont-containing clam Solemya reidi. Journal of Experimental Zoology. 256:130-134.   10.1002/jez.1402560203   AbstractWebsite

Solemya reidi is a gutless clam that contains intracellular, symbiotic sulfur-oxidizing chemoautotrophic bacteria in its gills. It lives in burrows in highly reducing muds rich in sulfide, a compound toxic at low levels to aerobic respiration. In these habitats there is wide variation in levels of O2 and sulfide, both of which are metabolic requirements for this symbiosis. In order to assess whether the animal tissues utilize aerobic or anaerobic ATP-generating pathways in the presence of sulfide, and to determine the sulfide concentrations that might induce a shift to anaerobiosis, clams were incubated in varying levels of sulfide and oxygen. Symbiont-free foot tissues from clams incubated in various levels of sulfide (50–500 μM) were analyzed for a common substrate (aspartate) and product (succinate) of invertebrate anaerobic metabolism. The concentrations of these metabolites were compared with those found in tissues of aerobic and anaerobic controls. Aerobic metabolism was maintained in animal tissues in the presence of up to 100 μM sulfide, levels at which maximum autotrophy has been previously reported; however, at higher concentrations, where inhibition of autotrophy has been reported, the onset of anaerobic pathways was evident. This use of anaerobic pathways was not due to the absence of O2, the classical definition of anaerobiosis, but rather to the inhibitory effect of sulfide on aerobic metabolism. The metabolic flexibility of this species in regard to energy metabolism is clearly advantageous living as it does at the interface between a highly oxic environment and an anoxic, highly reducing one.

Arndt, C, Schiedek D, Felbeck H.  1998.  Anaerobiosis in the hydrothermal vent tube-worm Riftia pachyptila. Cahiers De Biologie Marine. 39:271-273. AbstractWebsite
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Arndt, C, Gaill F, Felbeck H.  2001.  Anaerobic sulfur metabolism in thiotrophic symbioses. Journal of Experimental Biology. 204:741-750. AbstractWebsite

Hydrogen sulfide is generally accepted to be the energy source for the establishment of sulfur-oxidizing symbiotic communities. Here, we show that sulfur-storing symbioses not only consume but also produce large amounts of hydrogen sulfide. The prerequisite for this process appears to be the absence of oxygen, Anaerobic sulfide production is widespread among different thiotrophic symbioses from vent and non-vent sites (Riftia pachyptila, Calyptogena magnifica, Bathymodiolus thermophilus, Lucinoma aequizonata and Calyptogena elongata), The extent of H2S generation correlates positively with the amount of elemental sulfur stored in the symbiont-bearing tissues of the hosts. Sulfide production starts a few hours after anoxia sets in, with H2S initially accumulating in the circulatory system before it is excreted into the surrounding environment. We propose that not sulfate but the elemental sulfur deposited in the symbionts serves as a terminal electron acceptor during anoxia and is reduced to sulfide. In anoxia-tolerant symbioses such as L. aequizonata, anaerobic sulfur respiration may be important for producing maintenance energy to help the species survive several months without oxygen, The increased levels of cysteine in the gills of L. aequizonata may be caused by a lack of reoxidation due to the absence of oxygen.

Arndt, C, Schiedek D, Felbeck H.  1998.  Metabolic responses of the hydrothermal vent tube worm Riftia pachyptila to severe hypoxia. Marine Ecology-Progress Series. 174:151-158.   10.3354/meps174151   AbstractWebsite

The metabolic capabilities of the hydrothermal vent tube worm Riftia pachyptila to tolerate short- and long-term exposure to hypoxia were investigated. After incubating specimens under anaerobic conditions the metabolic changes in body fluids and tissues were analyzed over time. The tube worms tolerated anoxic exposure up to 60 h. Prior to hypoxia the dicarboxylic acid, malate, was found in unusually high concentrations in the blood (up to 26 mM) and tissues (up to 5 pmol g(-1) fresh wt). During hypoxia, most of the malate was degraded very quickly, while large quantities of succinate accumulated (blood: about 17 mM; tissues: about 13 mu mol g(-1) fresh wt). Volatile, short-chain fatty acids were apparently not excreted under these conditions. The storage compound, glycogen, was mainly found in the trophosome and appears to be utilized only during extended anaerobiosis. The succinate formed during hypoxia does not account for the use of malate and glycogen, which possibly indicates the presence of yet unidentified metabolic end products. Glutamate concentration in the trophosome decreased markedly during hypoxia, presumably due to a reduction in the autotrophic function of the symbionts during hypoxia. In conclusion, R. pachyptila is physiologically well adapted to the oxygen fluctuations frequently occurring in the vent habitat.

Arndt-Sullivan, C, Lechaire JP, Felbeck H.  2008.  Extreme tolerance to anoxia in the Lucinoma aequizonata symbiosis. Journal of Shellfish Research. 27:119-127.   10.2983/0730-8000(2008)27[119:ettait]2.0.co;2   AbstractWebsite

Our study describes the extraordinary capability of the endosymbiont-bearing bivalve Lucinoma aequizonata to tolerate environmental anoxia. The clam survives without oxygen for 262 days (50% mortality). The total quantity of glycogen in a specimen does not decrease significantly after long-term anoxia (10.5 mo). Common glycogen-derived anaerobic products (opines, lactate, succinate, acetate, and propionate) are only produced in minor quantities. This indicates either severe metabolic depression or the utilization of alternative energy sources. We have found indications that the endosymbiotic bacteria might function as an important carbon source for the bivalve. Transmission electron microscopy studies showed that the symbionts are largely degraded after L. aequizonata was incubated anoxically for 10.5 mo. Polyphosphates detected in symbiont granules by energy dispersive X-ray spectrometry (EDX) might represent an alternative energy source for the clam's metabolism under this stress situation.

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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.

Bright, M, Arndt C, Keckeis H, Felbeck H.  2003.  A temperature-tolerant interstitial worm with associated epibiotic bacteria from the shallow water fumaroles of Deception Island, Antarctica. Deep-Sea Research Part Ii-Topical Studies in Oceanography. 50:1859-1871.   10.1016/s0967-0645(03)00095-x   AbstractWebsite

A prominent not previously identified species of Monocelidae (Platyhelminthes, Proseriata) was found in the vicinity of fumarole activity at Fumarole Bay. The distribution of this animal and the metazoan meiobenthos in the vicinity of this area suggests that this species constitutes the most abundant species and the bulk of the biomass at these shallow water fumaroles. In contrast to the other metazoan meiofauna, the distribution of this species is positively correlated with the water temperature and gas emissions, indicating a preference for the areas around fumaroles. The range of temperature tolerated by this animal was determined in in vivo experiments to be at least 30-40degreesC. The outer surface the animals is colonized by apparently symbiotic bacteria, which are usually rod-like and approximately 0.68 mum wide and 2.07 mum long. The results of this study revealed a remarkable difference between shallow-water and deep-sea hydrothermal vent meiobenthic communities. Generalists capable of tolerating extreme abiotic conditions appear to dominate shallow-water vents, whereas endemism seems to be the rule in the deep-sea vents. (C) 2003 Elsevier Science Ltd. All rights reserved.

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Cary, SC, Vetter RD, Felbeck H.  1989.  Habitat characterization and nutritional strategies of the endosymbiont-bearing bivalve Lucinoma aequizonata. Marine Ecology-Progress Series. 55:31-45.   10.3354/meps055031   AbstractWebsite

A population of the lucinid bivalve Lucinorna aequizonata, with sulfur-oxidizing endosymbiotic bacteria in the gills, is restricted to a narrow depth range (500 ±10m) on the slope of the Santa Barbara Basin, California, USA. In this zone, the seawater just above the substratum is sub-oxic (O2 < 20 µM).The organically rich sediments in which these clams live are well mixed by bioturbation, which appears to maintain a redox condition limiting the extensive accumulation of hydrogen sulfide. However, thiol levels in the blood of the clams indicate an exposure to significant amounts of sulfide and/or thiosulfate apparently from randomly dispersed short-lived pockets of sulfidic mud that can be reached by the clam's burrowing vermiform foot. When the bivalves are incubated in the presence of hydrogen sulfide, thiosulfate is concentrated in the blood and apparently utilized by the bacteria for metabohc energy and the production of intracellular elemental sulfur. Laboratory growth experiments demonstrated that sulfide concentrations greater than 10 µM were detrimental to the host, even though the bacteria continued to accumulate elemental sulfur. The utilization of thiosulfate under near anaerobic conditions and the accumulation of intracellular elemental sulfur by the endosymbiotic bacteria coupled with the high availability of environmental nitrate and low molecular oxygen suggests a metabolic strategy analogous to the free-living sulfur oxidizer Thlobacillus denjtrificans. The δ13C values of the purified endosymbiont bacteria (-34.0 5 0.8‰) were significantly lighter than those of the host tissue (-29.0 +0.7‰)suggesting that in addition to the nutrition provided by the bacteria, over 25 % of the host carbon may be attributed to exogenous dissolved carbon which is in high concentrations in its natural habitat.

Cary, SC, Fisher CR, Felbeck H.  1988.  Mussel growth supported by methane as sole carbon and energy source. Science. 240:78-80.   10.1126/science.240.4848.78   AbstractWebsite

Symbioses between chemoautotrophic bacteria and several specialized marine invertebrates are well documented. However, none of these symbioses have been demonstrated to provide sufficient energy and carbon to the host to enable it to grow. Growth rates of seep mussels collected from hydrocarbon seeps off the coast of Louisiana were measured in a controlled environment where methane was the sole carbon and energy source. The growth rates increased to a maximum of 17.2 micrometers per day in response to methane and approached zero in the absence of methane. These mussels contain methanotrophic symbiotic bacteria in their gills, which suggests that these bacteria provide their hosts with a net carbon flux originating from methane.

Cary, C, Fry B, Felbeck H, Vetter RD.  1989.  Multiple trophic resources for a chemoautotrophic community at a cold water brine seep at the base of the Florida Escarpment. Marine Biology. 100:411-418.   10.1007/bf00391157   AbstractWebsite

The biological community that surrounds the hypersaline cold water brine seeps at the base of the Florida Escarpment is dominated by two macrofaunal species: an undescribed bivalve of the family Mytilidac and a vestimentiferan worm, Escarpia laminata. These animals are apparently supported by the chemoautotrophic fixation of carbon via bacterial endosymbionts. Water column and sediment data indicate that high levels of both sulfide and methane are present in surface sediments around the animals but absent from overlying waters. Stable isotopic analyses of pore water indicate that there are two sources of sulfide: the first is geothermal sulfide carried in groundwater leaching from the base of the escarpment, and the second is microbial sulfide produced in situ. The vestimentiferan E. laminata, and the mytilid bivalve (seep mussel) live contiguously but rely on different substrates for chemoautotrophy. Enzyme assays, patterns of elemental sulfur storage and stable isotopic analyses indicate that E. laminata relies on sulfide oxidation and the seep mussel on methane oxidation for growth.

Cary, SC, Felbeck H, Holland ND.  1989.  Observations on the reproductive biology of the hydrothermal vent tube worm Riftia pachyptila. Marine Ecology-Progress Series. 52:89-94.   10.3354/meps052089   AbstractWebsite

On the Hydronaut Expedition to 13"N on the East Pacific Rise, we made some observations on the reproductive biology of Riftia pachyptila relevant to larval dispersal, symbiont acquisition, and sperm transfer. Two females spawned in a pressure chamber about 15 h after collection. During each 30 min spawning episode, the relatively small (105pm), lipid-rich eggs were emitted in large numbers from the female gonopores and floated upward in still seawater at about 2 cm min^-1. Therefore, it is likely that early development takes place in deep water well above the vent habitat of the adults. Two males spawned in non-pressurized aquaria about 45 min after reaching the deck of the ship. Semen issuing from the male gonopores contained sperm bundles, each composed of several hundred sperm wlth remarkable detached acrosomes. Each bundle swam vigorously through seawater by the beating of all its flagella In unison Motilty was not inhibited by hydrogen sulfide concentratlons greater than those at the vent habitat. After swimmlng for about 15 min, the bundles broke up into individual sperm that were relatively immotile. It is reasonable to assume that sperm bundles swim from the male to the female's tube or body where they adhere by their detached acrosomes before disintegrating into individual sperm that subsequently ferhhze the eggs.

Childress, JJ, Fisher CR, Felbeck H, Girguis P.  2004.  On the edge of a deep biosphere: real animals in extreme environments. The subseafloor biosphere at mid-ocean ridges. ( Wilcock WSD, Delong EF, Kelley DS, Baross JA, Cary SC, Eds.).:41-49., Washington, DC: American Geophysical Union Abstract
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Childress, JJ, Felbeck H, Somero GN.  1987.  Symbiosis in the Deep-Sea. Scientific American. 256:114-121. AbstractWebsite
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Childress, JJ, Lee RW, Sanders NK, Felbeck H, Oros DR, Toulmond A, Desbruyeres D, Kennicutt MC, Brooks J.  1993.  Inorganic carbon uptake in hydrothermal vent tubeworms facilitated by high environmental pC02. Nature. 362:147-149.   10.1038/362147a0   AbstractWebsite

THE marine invertebrate Riftia pachyptila has a remarkable symbiosis with intracellular carbon-fixing sulphide-oxidizing bacteria which was first discovered at 2,450 m depth on the Galapagos Rift1-4. Such symbiotic arrangements have since been found in a variety of invertebrate taxa and habitat5,6. Studies of these symbioses have focused on temperature, sulphide and oxygen as critical environmental parameters5,7-9. As Riftia has a high growth rate and its symbionts are far removed from the host surface10,11, inorganic carbon supply to the symbionts has been recognized as a problem and host mechanisms to concentrate inorganic carbo have been posited12,13. Increased environmental CO2 partial pressure (pCO2) has not seriously been considered as a critical environmental parameter7,14. Here we report that elevated pCO2 (2.9 kPa) in the worms' environment is a determinant of internal total CO2 (SIGMACO2) and pCO2, facilitating CO2 transport and diffusion to the symbionts. We propose that elevated pCO2 is a potentially critical environmental factor for this species as well as for other chemoautotrophic symbioses.

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Distel, DL, Lane DJ, Olsen GJ, Giovannoni SJ, Pace B, Pace NR, Stahl DA, Felbeck H.  1988.  Sulfur-oxidizing bacterial endosymbionts: analysis of phylogeny and specificity by 16S rRNA sequences.. Journal of Bacteriology. 170:2506-2510. AbstractWebsite

The 16S rRNAs from the bacterial endosymbionts of six marine invertebrates from diverse environments were isolated and partially sequenced. These symbionts included the trophosome symbiont of Riftia pachyptila, the gill symbionts of Calyptogena magnifica and Bathymodiolus thermophilus (from deep-sea hydrothermal vents), and the gill symbionts of Lucinoma annulata, Lucinoma aequizonata, and Codakia orbicularis (from relatively shallow coastal environments). Only one type of bacterial 16S rRNA was detected in each symbiosis. Using nucleotide sequence comparisons, we showed that each of the bacterial symbionts is distinct from the others and that all fall within a limited domain of the gamma subdivision of the purple bacteria (one of the major eubacterial divisions previously defined by 16S rRNA analysis [C. R. Woese, Microbiol. Rev. 51: 221-271, 1987]). Two host specimens were analyzed in five of the symbioses; in each case, identical bacterial rRNA sequences were obtained from conspecific host specimens. These data indicate that the symbioses examined are species specific and that the symbiont species are unique to and invariant within their respective host species.

Distel, DL, Felbeck H.  1988.  Pathways of inorganic carbon fixation in the endosymbiont-bearing lucinid clam Lucinoma aequizonata. Part 1. Purification and characterization of the endosymbiotic bacteria. Journal of Experimental Zoology. 247:1-10.   10.1002/jez.1402470102   AbstractWebsite

Two simple techniques by which the sulfur-oxidizing endosymbiotic bacteria may be purified from the bacteriocyte tissues of the marine bivalve Lucinoma aequizonata, are described. Tissue homogenates are prepared from symbiont-containing tissues, and symbionts are recovered by centrifugation through gradients of Percoll density gradient medium. The high density of the endosymbionts (probably because of the presence of numerous sulfur deposits within the cells) allows clean, rapid, and efficient separation of these cells from host cells and cell constituents. Light and electron microscopy and enzymatic and biochemical techniques are used to demonstrate the identity, quality, and purity of the symbiont isolates from this lucinid clam. The techniques described here for L. aequizonata, have also been used successfully to purify sulfur-oxidizing endosymbionts from a variety of marine invertebrates, including the bivalves L. annulata, Lucina floridana, Calyptogena magnifica, and Codakia orbicularis, and from the vestimentiferan tubeworms Riftia pachyptila, and Tevnia jerichonana. Such preparations should prove useful for investigating these and similar sulfur-oxidizing symbioses.

Distel, DL, Felbeck H.  1987.  Endosymbiosis in the lucinid clams Lucinoma aequizonata, Lucinoma annulata and Lucina floridana: a reexamination of the functional morphology of the gills as bacteria-bearing organs. Marine Biology. 96:79-86.   10.1007/bf00394840   AbstractWebsite

A three-dimensional representation of the structure of the endosymbiont-containing gills of Lucinoma aequizonata, L. annulata and Lucina floridana was constructed using light and electron microscopy of fresh and plastic-embedded thin-sectioned samples. The gills of these lucinids are identical in overall structure, each being composed of three structurally and functionally distinct regions here called the ctenidial filament zone (CFZ), the transition zone (TZ), and the bacteriocyte zone (BZ). Rather than a simple medial extension of the filament tissue, the bacteriocyte tissue is organized as an array of cylindrical tubes, the walls of which are composed primarily of bacteriocyte cells covered by a thin microvillar epithelium. The physical relationship between the symbionts, the host tissues and the external environment are examined, and structural constraints on the potential functions of bacteria in this host-symbiont system are discussed.

Distel, DL, Felbeck H, Cavanaugh CM.  1994.  Evidence for phylogenetic congruence among sulfur-oxidizing chemoautotrophic bacterial endosymbionts and their bivalve hosts. Journal of Molecular Evolution. 38:533-542.   10.1007/bf00178852   AbstractWebsite

Sulfur-oxidizing chemoautotrophic (thioautotrophic) bacteria are now known to occur as endosymbionts in phylogenetically diverse bivalve hosts found in a wide variety of marine environments. The evolutionary origins of these symbioses, however, have remained obscure. Comparative 16S rRNA sequence analysis was used to investigate whether thioautotrophic endosymbionts are monophyletic or polyphyletic in origin and to assess whether phylogenetic relationships inferred among these symbionts reflect those inferred among their hosts. 16S rRNA gene sequences determined for endosymbionts from nine newly examined bivalve species from three families (Vesicomyidae, Lucinidae, and Solemyidae) were compared with previously published 16S rRNA sequences of thioautotrophic symbionts and free-living bacteria. Distance and parsimony methods were used to infer phylogenetic relationships among these bacteria. All newly examined symbionts fall within the gamma subdivision of the Proteobacteria, in clusters containing previously examined symbiotic thioautotrophs. The closest free-living relatives of these symbionts are bacteria of the genus Thiomicrospira. Symbionts of the bivalve superfamily Lucinacea and the family Vesicomyidae each form distinct monophyletic lineages which are strongly supported by bootstrap analysis, demonstrating that host phylogenies inferred from morphological and fossil evidence are congruent with phylogenies inferred for their respective symbionts by molecular sequence analysis. The observed congruence between host and symbiont phylogenies indicates shared evolutionary history of hosts and symbiont lineages and suggests an ancient origin for these symbioses.

Distel, DL, Felbeck H.  1988.  Pathways of inorganic carbon fixation in the endosymbiont-bearing lucinid clam Lucinoma aequizonata. Part 2. Analysis of the individual contributions of host and symbiont cells to inorganic carbon assimilation. Journal of Experimental Zoology. 247:11-22.   10.1002/jez.1402470103   AbstractWebsite

The incorporation of 14C from H14CO−3 into acid-soluble metabolites was examined in the endosymbiont-containing gills and purified symbionts of the lucinid clam Lucinoma aequizonata. HPLC, paper chromatography, and enzymatic techniques were used to identify and quantify compounds into which label was incorporated in continuous and pulse-labeling experiments. Both symbiont and host cells fix carbon in considerable quantities; however, each incorporates carbon into a distinctly different subset of compounds. In intact gills the initial carbon fixation product is malate. Label subsequently accumulates in succinate, glucose phosphate, glutamate, alanine, and glycogen. In the symbiont cells carbon is incorporated into aspartate, 3-phosphoglycerate, malate, and citrate. Purified symbionts incorporate carbon into the same compounds in the same proportions as do symbionts that are exposed to labeled H14CO−3 while still within the host tissues. Under the conditions tested, purified symbionts released no significant quantities of labeled compounds into the incubation medium.

Dufour, SC, Felbeck H.  2003.  Sulphide mining by the superextensile foot of symbiotic thyasirid bivalves. Nature. 426:65-67.   10.1038/nature02095   AbstractWebsite

In a symbiotic association between an invertebrate host and chemoautotrophic bacteria, each partner has different metabolic requirements, and the host typically supplies the bacteria with necessary reduced chemicals ( sulphide or methane). Some combination of anatomical, physiological and behavioural adaptations in the host often facilitates uptake and transport of reduced chemicals to the symbionts(1-4). We have studied five species of bivalve molluscs of the family Thyasiridae ( that is, thyasirids) three of which harbour chemoautotrophic bacteria. Here we show that the symbiotic bivalves extend their feet to form elongated and ramifying burrows in the sediment, most probably to gain access to reduced sulphur. Closely related bivalves ( including some thyasirid species) without bacterial symbionts show no comparable foot extension behaviour. The length and number of burrows formed by chemosymbiotic thyasirids are related to the concentration of hydrogen sulphide in the sediment. The burrows are formed by the foot of each bivalve, which can extend up to 30 times the length of the shell, and may be the most extreme case of animal structure elongation documented to date.

Dufour, SC, Felbeck H.  2006.  Symbiont abundance in thyasirids (Bivalvia) is related to particulate food and sulphide availability. Marine Ecology-Progress Series. 320:185-194.   10.3354/meps320185   AbstractWebsite

Many bivalve species with chemoautotrophic symbionts have mixotrophic diets and some of their nutritional requirements are met by particulate feeding. The symbionts require reduced compounds (such as sulphide) for their autotrophic production. As the concentration of both particulate food and sulphide can vary in their habitat, it has been suggested that symbiont numbers may vary in response. To address whether symbiont abundance can be influenced by the external medium, we compared symbiont. abundance (1) in specimens kept with or without particulate food, and (2) in specimens kept in sediments with low or high dissolved sulphide content. The relative surface area occupied by symbionts on semi-thin gill sections was determined for Thyasira flexuosa (and, in the sulfide experiment, for Parathyasira equalis and T sarsi) kept for up to 3 wk in experimental microcosms, where the quantity of particulate food or dissolved sulphide was manipulated. Symbiont abundance declined with time; the decline was greater in particle-starved thyasirids and in specimens kept in low sulphide. In the latter conditions, T flexuosa may have also had a greater symbiont digestion rate. The observed patterns may be due to a combination of increased symbiont uptake by the bivalve host, and reduced symbiont vigour under the imposed conditions. The flexible feeding mode of chemosymbiotic thyasirids may help them to survive in fluctuating environments.

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.

Duplessis, MR, Ziebis W, Gros O, Caro A, Robidart J, Felbeck H.  2004.  Respiration strategies utilized by the gill endosymbiont from the host lucinid Codakia orbicularis (Bivalvia : Lucinidae). Applied and Environmental Microbiology. 70:4144-4150.   10.1128/aem.70.7.4144-4150.2004   AbstractWebsite

The large tropical lucinid clam Codakia orbicularis has a symbiotic relationship with intracellular, sulfide-oxidizing chemoautotrophic bacteria. The respiration strategies utilized by the symbiont were explored using integrative techniques on mechanically purified symbionts and intact clam-symbiont associations along with habitat analysis. Previous work on a related symbiont species found in the host lucinid Lucinoma aequizonata showed that the symbionts obligately used nitrate as an electron acceptor, even under oxygenated conditions. In contrast, the symbionts of C orbicularis use oxygen as the primary electron acceptor while evidence for nitrate respiration was lacking. Direct measurements obtained by using microelectrodes in purified symbiont suspensions showed that the symbionts consumed oxygen; this intracellular respiration was confirmed by using the redox dye CTC (5-cyano-2,3-ditolyl tetrazolium chloride). In the few intact chemosymbioses tested in previous studies, hydrogen sulfide production was shown to occur when the animal-symbiont association was exposed to anoxia and elemental sulfur stored in the thioautotrophic symbionts was proposed to serve as an electron sink in the absence of oxygen and nitrate. However, this is the first study to show by direct measurements using sulfide microelectrodes in enriched symbiont suspensions that the symbionts are the actual source of sulfide under anoxic conditions.

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Felbeck, H, Childress JJ, Somero GN.  1983.  Biochemical interactions between molluscs and their symbionts. The mollusca Vol. 2, Environmental biochemistry and physiology. ( Hochachka PW, Ed.).:331-358., New York; London: Academic Press Abstract
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Felbeck, H.  1985.  CO2 fixation in the hydrothermal vent tube worm Riftia pachyptila (Jones). Physiological Zoology. 58:272-281. AbstractWebsite
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