The effect of copper and zinc on the metabolism of the mussel Mytilus edulis

The effects of copper and zinc on the metabolism of the mussel Mytilus edulis (L.) and its component tissues were studied. 500 ppm copper sodium citrate inhibited oxygen consumption of the whole animal and gill tissue, but no similar effect was observed on digestive gland tissue. 500 ppm zinc sodium citrate exerted no effect upon gill or digestive gland respiration, and neither metal salt affected the respiration of homogenates of gill, digestive gland or gonad. Direct observation of gill tissues during exposure to the metals revealed that 500 ppm copper sodium citrate caused inhibition of ciliary activity; exposure of tissues to 2 ppm Cu for 24 h resulted in only partial inhibition of the cilía. It is suggested that metabolic suppression noted in whole animals and gill tissues is due to the inhibition of an energy-consuming process such as ciliary activity rather than interference with respiratory enzyme systems.     

The importance of methane and thiosulfate in the metabolism of the bacterial symbionts of two deep-sea mussels

Undescribed hydrocarbon-seep mussels were collected from the Louisiana Slope, Gulf of Mexico, during March 1986, and the ultrastructure of their gills was examined and compared to Bathymodiolus thermophilus, a mussel collected from the deep-sea hydrothermal vents on the Galápagos Rift in March 1985. These closely related mytilids both contain abundant symbiotic bacteria in their gills. However, the bacteria from the two species are distinctly different in both morphology and biochemistry, and are housed differently within the gills of the two mussels. The symbionts from the seep mussel are larger than the symbionts from B. thermophilus and, unlike the latter, contain stacked intracytoplasmic membranes. In the seep mussel three or fewer symbionts appear to be contained in each host-cell vacuole, while in B. thermophilus there are often more than twenty bacteria visible in a single section through a vacuole. The methanotrophic nature of the seep-mussel symbionts was confirmed in ¹⁴C-methane uptake experiments by the appearance of label in both CO₂ and acid-stable, non-volatile, organic compounds after a 3 h incubation of isolated gill tissue. Furthermore, methane consumption was correlated with methanol dehydrogenase activity in isolated gill tissue. Activity of ribulose-1,5-biphosphate (RuBP) carboxylase and ¹⁴CO₂ assimilation studies indicate the presence of either a second type of symbiont or contaminating bacteria on the gills of freshly captured seep mussels. A reevaluation of the nutrition of the symbionts in B. thermophilus indicates that while the major symbiont is not a methanotroph, its status as a sulfur-oxidizing chemoautotroph, as has been suggested previously, is far from proven.     

Chemoautotrophic symbionts and translocation of fixed carbon from bacteria to host tissues in the littoral bivalve Loripes lucinalis (Lucinidae)

Specimens of Loripes lucinalis (Lucinidae) living in reducing sediments were collected near a sewage outfall at low tide on the Moulin Blanc beach, Brest, France, from January to March 1987. Electron microscope studies revealed numerous Gram-negative-type bacteria in the gill cells. Ribulosebiphosphate carboxylase, a diagnostic enzyme of the Calvin-Benson cycle of CO₂-fixation was measured only in the gill extracts. Various tissues of L. lucinalis were examined for activity of APS reductase, (EC 1.8.99.2), ATP sulphurylase (EC 2.7.7.4) and rhodanese (EC 2.8.1.1), enzymes involved in sulphide oxidation. APS reductase was only found in symbiont-containing tissues, i.e., gills. These enzymatic studies characterise the symbionts as chemoautotrophic sulphide-oxidizing bacteria. Histoautoradiography demonstrated that part of the carbon dioxide fixed by symbiotic bacteria in the gills is translocated to symbiont-free tissues of the bivalve. The ultrastructure of the gill is detailed and a nomenclature based on established and new terminology is proposed to describe the various cellular types comprising the gill filament.     

Elemental sulfur in the gills of three species of clams containing chemoautotrophic symbiotic bacteria: a possible inorganic energy storage compound

Sulfur content and fine structure were studied for tissues of three species of clams, Lucinoma annulata, Calyptogena elongata and Lucina floridana, which inhabit sulfide-rich environments and whose gills harbor symbiotic sulfur bacteria. Lucinoma annulata and C. elongata were dredged from the Santa Barbara basin, California, USA, at a depth of 480 to 490 m, and Lucina floridana were dug from below the roots of seagrasses in Saint Joseph Bay, Florida, at a depth of 0.25 to 2m. Foot tissue of Lucinoma annulata, without symbionts, had a total sulfur content of 1.4±0.1 (SD) mg 100 mg^-1 dry weight of tissue (%DW). The symbiont-containing gill tissue of different individuals of L. annulata varied in color from dark red to pale yellow, and the total sulfur content was 2.5±0.4% DW in red gills and was 5.6±3.3 % DW in the yellowest gills. Maintenance of L. annulata in the laboratory for 21 d in the absence of sulfide resulted in the loss from the gill of yellow deposits which were elemental sulfur in the form of liquid-crystalline sulfur globules rather than solid orthorhombic sulfur crystals. The foot tissue did not contain elemental sulfur. When examined by freeze-etch microscopy, sulfur globules were found only within bacteria and not in the animal host cytoplasm. Sulfur globules were confined to the periplasmic space of the bacteria. C. elongata and Lucina floridana resembled Lucinoma annulata in the physical form and distribution of elemental sulfur. The absence of elemental sulfur in the animal cytoplasm suggests that its formation from sulfide is not a detoxification scheme to protect animal tissue from sulfide toxicity. The sulfur deposits probably represent inorganic energy reserves that permit the symbiotic bacteria to function even during the temporary absence of external sulfide.     

Anatomical and experimental evidence for particulate feeding in<Emphasis Type="Italic"> Lucinoma aequizonata</Emphasis> and<Emphasis Type="Italic"> Parvilucina tenuisculpta</Emphasis> (Bivalvia: Lucinidae) from the Santa Barbara Basin

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 hosts 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.Electronic Supplementary Material Supplementary material is available in the online version of this article at Communicated by P.W. Sammarco, Chauvin     

Persistence,morphology, and nutritional state of a gastropod hosted bacterial symbiosis in different levels of hydrothermal vent flux

The limpet, Lepetodrilus fucensis McLean, is found in prominent stacks around hydrothermal vents on the Juan de Fuca Ridge. L. fucensis hosts a filamentous episymbiont on its gill lamellae that may be ingested directly by the gill epithelium. To assess the persistence of this symbiosis I used microscopy to examine the gills of L. fucensis from sites representing its geographic range and different habitats. The symbiosis is present on all the specimens examined in this study, including both sexes and a range of juvenile and adult sizes. Next, I aimed to determine if patterns in bacterial abundance, host condition, and gill morphology support the hypotheses that the bacteria are chemoautotrophic and provide limpets with a food resource. To do so, I compared specimens from high and low flux locations at multiple vents. My results support the above hypotheses: (1) gill bacteria are significantly less abundant in low flux where the concentrations of reduced chemicals (for chemoautotrophy) are negligible, (2) low flux specimens have remarkably poor tissue condition, and (3) the lamellae of high flux limpets have greater surface area: the blood space and bacteria-hosting epithelium are deeper and have more folds than low flux lamellae, modifications that support higher symbiont abundances. I next asked if the morphology of the lamellae could change. To test this, I moved high flux limpets away from a vent and after 1 year the lamellar depth and shape of the transplanted specimens resembled low flux gills. Last, I was interested in whether bacterial digestion by the gill epithelium is a significant feeding mechanism. As bacteria-like cells are rarely apparent in lysosomes of the gill epithelium, I predicted that lysosome number would be unrelated to bacterial abundance. My data support this prediction, suggesting that digestion of bacteria by the gill epithelium probably contributes only minimally to the limpet’s nutrition. Overall, the persistence and morphology of the L. fucensis gill symbiosis relates to the intensity of vent flux and indicates that specimens from a variety of habitats may be necessary to characterize the morphological variability of gill-hosted symbioses in other molluscs.     

A new bathymodioline mussel symbiosis at the Juan de Fuca hydrothermal vents

Until recently, the only major hydrothermal vent biogeographic province not known to include bathymodioline mussels was the spreading centers of the northeast Pacific, but deep-sea dives using DSV Alvin on the Endeavor segment of the Juan de Fuca Ridge (47°56N 129°06W; ∼2,200 m depth) in August 1999 yielded the only recorded bathymodioline mytilids from these northeastern Pacific vents. One specimen in good condition was evaluated for its relatedness to other deep-sea bathymodioline mussels and for the occurrence of chemoautotrophic and/or methanotrophic symbionts in the gills. Phylogenetic analyses of the host cytochrome oxidase I gene show this mussel shares evolutionary alliances with hydrothermal vent and cold seep mussels from the genus Bathymodiolus, and is distinct from other known species of deep-sea bathymodiolines, suggesting this mussel is a newly discovered species. Ultrastructural analyses of gill tissue revealed the presence of coccoid bacteria that lacked the intracellular membranes observed in methanotrophic symbionts. The bacteria may be extracellular but poor condition of the fixed tissue complicated conclusions regarding symbiont location. A single gamma-proteobacterial 16S rRNA sequence was amplified from gill tissue and directly sequenced from gill tissue. This sequence clusters with other mussel chemoautotrophic symbiont 16S rRNA sequences, which suggests a chemoautotrophic, rather than methanotrophic, symbiosis in this mussel. Stable carbon (δ¹³C = −26.6%) and nitrogen (δ¹⁵N = +5.19%) isotope ratios were also consistent with those reported for other chemoautotroph-mussel symbioses. Despite the apparent rarity of these mussels at the Juan de Fuca vent sites, this finding extends the range of the bathymodioline mussels to all hydrothermal vent biogeographic provinces studied to date.     

Methanotrophic symbiont location and fate of carbon incorporated from methane in a hydrocarbon seep mussel

Seep Mytilid Ia (SMIa), an undescribed mussel found at hydrocarbon seeps in the Gulf of Mexico, harbors intracellular methanotrophic symbionts. Two techniques were used to address the hypothesis that host digestion of symbionts is a significant mechanism of carbon transfer from symbiont to host in the SMIa association: lysosomal enzyme cytochemistry and ¹⁴C tissue autoradiography. Acid phosphatase activity was consistently localized in the Golgi apparatus and associated vesicles of gill cells, but was detected around bacteria in only three of approximately 50 bacteriocytes examined. These results indicate that the cellular equipment necessary for lysosomal digestion of symbionts is present in host bacteriocytes, but that acid phosphatase activity in symbiont vacuoles is rare at a given point in time. Tissue autoradiography was conducted with mussels collected in September 1992 to document carbon fixation by symbionts and follow the time course of transfer to host tissues. No asymbiotic host cell type showed a significant increase in relative grain density until at least 1 d after the end of incubation with ¹⁴C-methane. The ratio of label in the basal portion of bacteriocytes to total bacteriocyte label did not show a significant increase until 10 d after the end of the incubation period, indicating a slow increase of labeled carbon in the putative residual bodies, containing the remnants of lysosomal digestion. These results are consistent with the hypothesis that host digestion of symbionts is one route of nutrient acquisition in SMIa. Intracellular methanotrophic bacteria were found outside of the gill in SMIa juveniles, in mantle and foot epithelial tissues previously believed to be symbiont-free. These extra-gill symbionts and their host cells are morphologically similar to their gill counterparts and, like the gill symbionts, actively fix carbon from methane. Received: 29 March 1997 / Accepted: 12 May 1997     

The gill symbiont of the hydrothermal vent mussel Bathymodiolus thermophilus is a psychrophilic,chemoautotrophic, sulfur bacterium

Certain hydrothermal vent invertebrates, e.g. Riftia pachyptila and Calyptogena magnifica, are clearly established as harboring dense populations of chemoautotrophic sulfur bacteria in specialized tissues. By contrast, the physiological characteristics of the abundant intracellular gill symbiont of the vent mussel Bathymodiolus thermophilus have been questioned. The low activities of enzymes diagnostic for CO₂ fixation (Calvin cycle) and for sulfur-driven energy generation, as measured by other investigators, have been attributed to bacterial contamination of the gill surface. Based on research at the Galápagos Rift hydrothermal vents in 1988 and subsequent laboratory experiments, the current study confirms that the B. thermophilus symbiont is a psychrophile for which thiosulfate and sulfide stimulate CO₂ fixation. It strongly indicates that the symbiont is a chemoautotroph by establishing the following: (1) Sulfide and thiosulfate can stimulate CO₂ fixation by partially purified symbionts by up to 43-fold and 120-fold, respectively; (2) the ribulose-1,5-bisphosphate carboxylase/oxygenase activity of the symbiont is sufficient to account for its sulfide- or thiosulfate-stimulated CO₂ incorporation; (3) the symbiont's molar growth yield on thiosulfate, as judged by CO₂ incorporation, is indistinguishable from that of free-living chemoautotrophs. Due to the high protein-degrading activity of B. thermophilus gill lysate, it is also suggested that host lysis of symbionts plays a more important role in the nutrition of the vent mussel than in R. pachyptila or C. magnifica, for which no comparable protein-degrading activity was found.     

Digestive enzymes in marine invertebrates from hydrothermal vents and other reducing environments

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, -glucuronidase and leucineaminopeptidase 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 -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.     

Association of bacteria with larvae of the gutless protobranch bivalve Solemya reidi (Cryptodonta: Solemyidae)

Rod-shaped bacteria were consistently observed by transmission electron microscopy in the locomotory test of larvae and in the perivisceral cavity of post-larvae of Solemya reidi, a gutless protobranch bivalve known to possess intracellular chemoautotrophic bacterial symbionts in the adult gill. Bacteria develop within granular vesicles in the larval test, where they either remain to be ingested at metamorphosis, or are released into the space separating the test and embryo, to be subsequently ingested through the larval mouth. In either case, bacteria lie within the perivisceral cavity following metamorphosis. Bacteria were not seen either in or on gametes or in gills of juveniles. It is hypothesized that these bacteria represent a transmission stage of the gill symbionts present in adult S. reidi and are not evident in gametes or gills of juveniles due to cryptic packaging within granular vesicles. Perpetuation of this symbiosis would therefore be assured through vertical transmission, as is typical of other marine invertebrate-bacteria endosymbioses.Harbor Branch Oceanographic Institution Contribution No. 602     

Nutrition and development of brooded embryos in the brittlestar Amphipholis squamata: do endosymbiotic bacteria play a role?

To identify sources of nutrition potentially available to the yolk-deficient embryos of the brooding brittlestar Amphipholis squamata Della Chiaje, (= Axiognathus squamata, Thomas 1966), specimens were collected intertidally at all seasons (1986 through 1987) from Odiorne Point, Rye, New Hampshire and from Appledore Island, Isles of Shoals, Maine, USA. Ultrastructural, autoradiographic and immunohistochemical studies were made of adults and brooded embryos. Adult and embryonic tissues have morphological adaptations which support healthy, symbiotic bacteria (5 to 9 x 10⁶ colony forming units/adult brittlestar), while autoradiographic studies indicate direct uptake of labeled amino acids by eukaryotic host tissues and bacteria. Cell envelopes of subcuticular bacteria suggest that they are Gram negative and may belong in the genus Vibrio. Based on immunohistochemical localization, it appears that a single type of bacterium is present in large numbers under the cuticles of embryos and adults of A. squamata. This is the first study of the relationship between an echinoderm and a bacterium which includes isolation and immunohistochemical verification of the identity of the bacterial symbiont.     

Effects of cadmium on metallothionein and histology in gills of tilapia (Oreochromis niloticus) at different salinities

The objectives of this study were to evaluate the effects of sublethal cadmium concentrations on the levels of cadmium, metallothionein (MT) and histological changes in gills of East Java strain tilapia (Oreochromis niloticus) at different salinity levels. The levels of cadmium in control gills were not significantly different at 0, 5 and 10 practical salinity unit (PSU). The cadmium concentrations in gills of cadmium-exposed fish were significantly higher at 0 PSU than at 5, 10 and 15 PSU. The MT concentrations in control gills were not significantly different at 0, 5, and 10 PSU. The MT concentrations of cadmium-exposed fish were significantly higher than those in respective control groups at 0, 5 and 10 PSU. Significant gill damage occurred in fish exposed to cadmium at lower salinity. The epithelial lifting was noted at gills of fish exposed to 2.5 mg/L of cadmium at 0 PSU, and telangiectasis was observed at gills exposed to 5 mg/L of cadmium at 0 PSU. The level of gill damage decreased with increasing salinity of media. The increased MT and histological changes in gills of our findings could be a protective response of animals to toxic effect of cadmium.     

Allometry of gill weights,gill surface areas,and foot biomass δ<Superscript>13</Superscript>C values of the chemoautotroph–bivalve symbiosis<Emphasis Type="Italic"> Solemya velum</Emphasis>

The protobranch bivalve Solemya velum Say, 1822 has large gills, which harbor chemolithoautotrophic bacteria that supply the majority of the clams organic carbon. A substantial portion of the CO₂, O₂, H₂S, and other nutrients necessary for symbiont autotrophy and host heterotrophy are acquired from the environment through the gills, whose large size may be necessary to facilitate the acquisition of sufficient O₂ from S. velums habitat to meet the combined demands of the host and symbionts. Large gills may also result in an oversupply of CO₂, which may in turn be responsible for the isotopically depleted ¹³C values observed in S. velum biomass (–31 to –34). Alternatively, gill hypertrophy may simply be an adaptation to house a large population of symbionts adjacent to their environmental source of dissolved gases and other nutrients. To better understand gill function in this symbiosis, gill weights, gill surface areas, and foot ¹³C values were measured as a function of total weights. S. velum gill weights were found to be a substantial portion of total clam weight, averaging 38% of wet weight, compared to nonsymbiotic protobranch bivalves Yoldia limatula Say, 1831 (5%) and Nucula proxima Say, 1822 (11%). Gill weights are a smaller percentage of total weight in larger individuals; the allometric equation for gill weight (G) as a function of total weight (M) is G=0.26M^0.85. Dry weights scale similarly. Gill surface areas are immense; the average gill surface area measured was 107 cm² g^–1 total soft tissue wet weight, the highest value for any marine invertebrate. Gill surface area (SA) also scales with size (SA=69.8M^0.85). When gill surface areas were calculated with respect to gill wet weights, they did not scale with size. The ¹³C values do not scale with size either, consistent with high rates of CO₂ supply at all sizes. Extraordinarily high rates of CO₂ supply relative to demand are supported by a model for CO₂ delivery based on Ficks law and the allometric relationship between surface areas and total weight, consistent with a role for large gill surface areas in the generation of isotopically depleted tissue ¹³C values.Communicated by J. P. Grassle, New Brunswick     

Gill and intestinal Na+-K+ ATPase activity, and estimated maximal osmoregulatory costs, in three high-energy-demand teleosts: yellowfin tuna (Thunnus albacares), skipjack tuna (Katsuwonus pelamis), and dolphin fish (Coryphaena hippurus)

We hypothesize that the morpho-physiological adaptations that permit tunas to achieve maximum metabolic rates (MMR) that are more than double those of other active fishes should result in high water and ion flux rates across the gills and concomitant high osmoregulatory costs. The high standard metabolic rates (SMR) of tunas and dolphin fish may, therefore, be due to the elevated rates of energy expenditure for osmoregulation (i.e. teleosts capable of achieving exceptionally high MMR necessarily have SMR). Previous investigators have suggested a link between activity patterns and osmoregulatory costs based on Na⁺-K⁺ ATPase activity in the gills of active epipelagic and sluggish deep-sea fishes. Based on these observations, we conclude that high-energy-demand fishes (i.e. tunas and dolphin fish) should have exceptionally elevated gill and intestinal Na⁺-K⁺ ATPase activity reflecting their elevated rates of salt and water transfer. To test this idea and estimate osmoregulatory costs, we measured Na⁺-K⁺ ATPase activity (V _max) in homogenates of frozen samples taken from the gills and intestines of skipjack and yellowfin tunas, and the gills of dolphin fish. As a check of our procedures, we made similar measurements using tissues from hybrid red tilapia (Oreochromis mossambicus ×O. niloticus). Contrary to our supposition, we found no difference in Na⁺-K⁺ ATPase activity per unit mass of gill or intestine in these four species. We estimate the cost of osmoregulation to be at most 9% and 13% of the SMR in skipjack tuna and yellowfin tuna, respectively. Our results, therefore, do not support either of our original suppositions, and the cause(s) underlying the high SMR of tunas and dolphin fish remain unexplained. Received: 7 September 2000 / Accepted: 4 December 2000     

Possible strategy for the survival of marine bacteria under starvation conditions

A population of a psychrophilic marine vibrio (Ant-300) suspended at a low cell density in natural seawater (SW) or artificial seawater (ASW) showed an initial 200-fold increase in cell numbers. Ant-300 suspended in ASW at various densities showed a magnified initial increase in numbers as well as increased longevity as the population density decreased. The magnitude of the initial increase and the viability of the cells after 7 weeks continued incubation were the same whether the cells were suspended in SW, ASW amended with amino acids, or organic-free ASW. Continued incubation (long-term starvation) of a culture of Ant-300 at low cell densities in ASW showed that after 70 weeks over 15 times the orginal number of cells were still viable. When compared to the starvation survival of other bacceria, Ant-300 exceeds the longest reported starvation survival by at least 2.5 times. Our data indicate that Ant-300 is especially adapted for survival at low nutrient concentrations and low population densities due to a sustained increase in cell numbers that may represent a species survival mechanism for marine bacteria.Technical Paper No. 4493, Oregon Agricultural Experiment Station.     

Interactions between metals accumulated in the narrow-clawed crayfish Astacus leptodactylus (Eschscholtz, 1823) in Dikilitaş Lake,Turkey

The accumulations of Al, Cd, Cr, Cu, Fe, Ni, Pb and Zn in the exoskeleton, gills, hepatopancreas and abdominal muscles of crayfish Astacus leptodactylus (Eschscholtz, 1823) were determined. The strongest correlation observed was between Cr and Ni in the gills (r?=?0.904); moderate to strong correlations between Al, Cr, Fe, Ni and Cu were also observed in gill tissue. Disregarding the gills, the strongest correlation was found between Cu and Zn in the hepatopancreas (r?=?0.808); the correlation between these two metals might have been a result of metallothionein activity. The accumulation of Pb was found to correlate with that of Cd in the exoskeleton, Cd and Zn in the gills, Zn and Cu in the hepatopancreas and Cu in the abdominal muscle. None of these correlations were present in lakewater and sediment samples, suggesting that the crayfish metabolism may be responsible for the co-accumulation of metal–metal pairs. As all correlations in non-gill tissues are observed between divalent metals, a shared transporter such as divalent metal transporter 1 might be involved in the accumulation of these metals.     

Morphological adaptations to chronic hypoxia in deep-sea decapod crustaceans from hydrothermal vents and cold seeps

Animals inhabiting hydrothermal vents and cold seeps face conditions that are challenging for survival. In particular, these two habitats are characterized by chronic hypoxia, sometimes reaching complete anoxia. The characteristics of the scaphognathite and gills were studied in four species of shrimp and three species of crabs from hydrothermal vents and cold seeps, in order to highlight potential adaptations that could enhance oxygen acquisition in comparison with shallow-water relatives. All the vent and seep species studied here exhibit significantly larger scaphognathites, likely allowing more water to flow over their gills per stroke of this appendage. This is probably more energetically efficient that prolonged hyperventilation. In contrast to annelids, vent and seep decapods usually do not possess enlarged gills, a phenomenon likely due to the physical limitations imposed by the size of the gill chamber. In the vent shrimp Rimicaris exoculata and the vent crab Bythograea thermydron, however, there is a significantly higher specific gill surface area linked to a higher number of lamellae per gram of gill. Again in contrast to annelids, the diffusion distance through the gills is not strikingly different between the vent shrimp Alvinocaris komaii and the shallow-water species Palaemon spp. This may indicate that the epithelium and cuticle of the decapod gills are already optimized for oxygen uptake and that reducing the thickness of these compartments is not physically possible without affecting the physical integrity of the gills.     

悬浮物对褐牙鲆抗氧化酶活性及相关基因表达的影响

为探究褐牙鲆(Paralichthys olivaceus)幼鱼抗氧化系统酶活力及相关基因表达在悬浮物胁迫下的变化情况,设计了浓度为5 000、10 000 mg·L-1悬浮物水体对褐牙鲆(14.53 cm±1.58 cm)肌肉、肝脏、鳃及血液总超氧化物歧化酶(T-SOD)、谷胱甘肽转移酶(GST)、过氧化氢酶(CAT)酶活力及SOD2、GST、CAT的mRNA转录水平表达变化情况。结果显示:在悬浮物胁迫24 h或者48 h时,4种组织3种酶活力具有升高的趋势(P0.05);4种组织的T-SOD酶活力在96 h均高于对照组(P0.05),肌肉、鳃丝及血液中SOD2基因相对表达量96 h实验组低于对照组(P0.05);肌肉中CAT酶活力呈现先升高再降低趋势,鳃中CAT基因相对表达量呈现先降低、再升高、再降低的趋势;肝脏、鳃、血液中GST酶活力在悬浮物胁迫下呈现升高趋势,4种组织GST基因相对表达量在12~24 h时呈现升高趋势。研究表明:悬浮物对褐牙鲆抗氧化酶活力及相关基因的表达具有一定的影响,血液中3种酶活力变化幅度最大,鳃中3种基因相对表达水平变化幅度最大,这与血液及鳃参与呼吸作用过程有关;抗氧化酶活性及基因相对表达变化趋势并不完全一致。本研究可为揭示褐牙鲆应对悬浮物胁迫的耐受机制及褐牙鲆耐悬浮物品种选育提供基础数据。     

Histopathology of cerebro neuronal cells in freshwater snail Bellamya bengalensis: impact on respiratory physiology,by acute poisoning of mercuric and zinc chloride

Mercuric (Hg) and zinc (Zn) chloride toxicity was investigated in cerebroneuronal cells and gills of Bellamya bengalensis using sublethal concentrations under lab conditions. Freshwater snail B. bengalensis was exposed to mean LC₅₀ concentration (1.56 ppm and 12.7 ppm) of Hg and Zn chloride, respectively. Bioaccumulation of Hg and Zn was observed in nervous and gill tissue in proportion to the time of exposure. Respiratory mechanisms and rate of oxygen consumption was depleted by both metals. Histopathological alterations in cerebro neuronal cells (giant, large, medium, and small) and gill filamental epithelia were apparent in Hg and Zn-exposed snails. Histopathology demonstrated increased cytoplasmic basophilia, extreme indentation of plasma membrane, karyolitic and eccentric nuclei, nuclear envelope with irregular size, and shrunken appearance of cerebroneuronal cells. Histologically, gill filamental epithelia showed hypertrophy, enlarged ciliated margins reduced length of cilia, nuclear dilations, thickening of basal lamina, and hemocytic accumulations in induced cells and severe loss of goblet mucus cells at the tip. Histopathology was accompanied by dysfunctioning cilia with decreased rate of respiration. Overall, neuronal impairment with damaged gill filament produced improper gaseous exchange leading to sluggish movement.