The razor clam Sinonovacula constricta uses the strategy of conversion of toxic ammonia to glutamine in response to high environmental ammonia exposure.

High ammonia can inhibit the survival and growth, and even cause mortality of razor clam (S. constricta). The accumulation of ammonia to lethal concentrations in some invertebrates may be partially prevented by converting some of the ammonia into glutamine (Gln). Glutamine dehydrogenase (GDH) and glutamine synthetase (GS) have been widely implicated a central role in response to ammonia stress. However, the molecular and physiological response of GDH and GS to ammonia alterations has not yet been determined in clams. To investigate the possible participatory role of GDH and GS genes in altered ammonia conditions, we have cloned their gene sequences and examined the mRNA expression and western blotting under ammonia exposure in S. constricta (ScGDH and ScGS), and detected the levels of GS and GDH, and the content of glutamate (Glu) and Gln. The full-length cDNA of ScGDH was 3924 bp, with a 1629 bp open reading frame (ORF) encoding a 542 amino-acid polypeptide. The complete cDNA sequence for ScGS had 2739 bp with an ORF of 1110 bp encoding 369 amino acids. To investigate ammonia detoxification strategies, the clams were exposed to ammonia for 96 h at four different concentrations (0, 100, 140, and 180 mg/L). Exposure to ammonia resulted in a significant increase of glutamate concentration and Gln in the haemocytes. GDH activity, GDH relative mRNA and protein expression, GS activity, GS relative mRNA and protein expression increased significantly and showed a pronounced time and dosage interaction in the liver. The results suggested that the protective strategies of Gln formation existed in S. constricta, which could convert ammonia to non- or less toxic nitrogenous compounds on the exposure of ammonia. Glutamate content in the haemocytes increased significantly, which is to ensure sufficient Glu to meet the needs for GS to catalyze the conversion of ammonia to Gln. We proposed that the induction of Glu synthesis-related genes and the subsequent formation of the active protein occurred in preparation for the increased capacity of the body to convert ammonia, into Gln. The results of this study suggested that GDH and GS play an important role in the synthesis of Gln, emphasizing, the protective strategies of Gln formation in S. constricta convert ammonia to nontoxic or less toxic nitrogenous compounds upon exposure to ammonia.

Purification, biochemical and biophysical characterization of lysosomal ß-D-glucuronidase from an edible freshwater mussel, Lamellidens corrianus.

A lysosomal glycosidase, ß-glucuronidase, has been purified to homogeneity, from the soluble extracts of a freshwater mussel, L. corrianus, by a series of chromatography techniques involving phenyl-Sepharose, ion exchange, affinity and gel filtration chromatography. In native PAGE, ß-glucuronidase resolved into a single band and the molecular mass determined by gel filtration chromatography was found to be 250 kDa. Zymogram analysis with 4-methyl umbelliferyl ß-glucuronide substrate validated the purified enzyme as ß-glucuronidase. In SDS-PAGE, the purified enzyme was resolved into four sub-units with molecular weights around 90, 75, 65, and 50 kDa, respectively, and two of the subunits (90 and 50 kDa) cross-reacted with human ß-glucuronidase antiserum. The optimum pH and temperature of the purified glycosidase were 5.0 and 70 °C, respectively. The enzyme kinetics parameters, substrate affinity (KM) and maximum velocity (Vmax) of the purified protein estimated with p-nitrophenyl ß-D-glucuronide were 0.457 mM and 0.11867 µmol-1 min-1 mL-1, respectively. The secondary structure of ß-glucuronidase was determined in the far-UV range (190 nm to 230 nm) using CD spectroscopy. Heat denaturation plots determined by CD spectroscopy showed that the purified enzyme was stable up to 70 °C.

Effect of sublethal gradient concentrations of nickel on postlarvae of Penaeus monodon, Perna viridis and Terapon jarbua: Enzyme activities and histopathological changes.

The present study evaluates the enzyme activities and histopathological changes in the post larvae (PL) of shrimp (Penaeus monodon), green mussel (Perna viridis) and fingerlings of crescent perch (Terapon jarbua) exposed to sublethal gradient concentrations of Nickel (Ni). The median lethal concentration (LC50) values were 2.49, 66.03 and 43.92 mg Ni L-1 derived for the PL of shrimp, green mussel and fish fingerlings respectively. No Observed Effect Concentration (NOEC), Lowest Observed Effect Concentration (LOEC) and chronic values of the PL of shrimp were 46.5, 73.0 and 58.3 µg Ni L-1 derived for the 21-d survival endpoint. The NOEC, LOEC and chronic values for the 30-d survival endpoint of the green mussels and fish fingerlings were 4.6, 6.32, 5.4 and 1.95, 2.6, 2.25 mg Ni L-1 respectively. The isoforms of esterase, superoxide dismutase and malate dehydrogenase activities in the whole body tissues of test organisms were studied by native polyacrylamide gel electrophoresis after exposure to Ni. Histological examination of compound eye sections of shrimp revealed deformation, compression, fusion and detachement in the corneal cells from the corneal facet of the ommatidia indicating cellular anomalies due to Ni toxicity. Gill sections of the green mussel witnessed reduced haemolymph in sinuses of gill filaments, degenerative changes in interfilamentous junction and necrosis of frontal ciliated epithelial cells with vacuoles after exposure to Ni. Nickel affects the vision of shrimp and fish fingerlings, gills and byssus of green mussels.

Purification and characterization of a novel ß-1,3-glucanase from Arca inflata and its immune-enhancing effects.

A novel ß-1,3-glucanase from Arca inflata was purified using chromatography methods. It was determined as a glycoprotein comprising 23.65% carbohydrate content with O-linked glycan and showed specific activity of 90.01 ±â€¯1.2 U/mg against laminarin. The optimal pH and temperature for the activity of the glucanase were 6.0 and 40 °C, respectively. The affinity parameter of the glucanase using laminarin was determined as Kd = 13.09 µM. The activity of the glucanase was 27 ±â€¯2.6% enhanced by 2-mM Mn2+ ions and inhibited by 40-50% using 2-mM Zn2+, Cu2+, or Ba2+ ions. The glucanase showed an endo-type cleavage mode and hydrolyzed laminarin into glucoses, disaccharides, trioligosaccharides, and tetraoligosaccharides. Otherwise, the glucanase exhibited immune-enhancing effects via significantly increasing the phagocytic activity of macrophages and inducing the release of nitric oxide, tumor necrosis factor α, and interleukin-6 in RAW264.7 cells. It might be used as a bifunctional additive for the food industry.

Lipid-protein interactions in mitochondrial membranes from bivalve mollusks: molecular strategies in different species.

The mitochondrial F1FO-ATPase, the key enzyme in cell bioenergetics, apparently works in the same way in mollusks and in mammals. We previously pointed out a raft-like arrangement in mussel gill mitochondrial membranes, which apparently distinguishes bivalve mollusks from mammals. To explore the relationship between the microenvironmental features and the enzyme activity, the physico-chemical features of mitochondrial membranes and the F1FO-ATPase activity temperature-dependence are here explored in the Manila clam (Ruditapes philippinarum). Similarly to the mussel, clam gill mitochondrial membrane lipids exhibit a high sterol content (42 mg/g protein), mainly due to phytosterols (cholesterol only attains 42% of total sterols), and abundant polyunsaturated fatty acids (PUFA) (70% of total fatty acids), especially of the n-3 family. However, the F1FO-ATPase activation energies above and below the break in the Arrhenius plot (22.1 °C) are lower than in mussel and mammalian mitochondria. Laurdan fluorescence spectroscopy analyses carried out at 10 °C, 20 °C and 30 °C on mitochondrial membranes and on lipid vesicles obtained from total lipid extracts of mitochondria, indicate a physical state without coexisting domains. This mitochondrial membrane constitution, allowed by lipid-lipid and lipidprotein interactions and involving PUFA-rich phospholipids, phytosterols (much more diversified in clams than in mussels) and proteins, enables the maintenance of a homogeneous physical state in the range 10-30 °C. Consistently, this molecular interaction network would somehow extend the temperature range of the F1FO-ATPase activity and may contribute to clam resilience to temperature changes.

Effects of multi-walled carbon nanotube materials on Ruditapes philippinarum under climate change: The case of salinity shifts.

The toxicity of carbon nanotubes (CNTs) is closely related to their physico-chemical characteristics as well as the physico-chemical parameters of the media where CNTs are dispersed. In a climate change scenario, changes in seawater salinity are becoming a topic of concern particularly in estuarine and coastal areas. Nevertheless, to our knowledge no information is available on how salinity shifts may alter the sensitivity (in terms of biochemical responses) of bivalves when exposed to different CNTs. For this reason, a laboratory experiment was performed exposing the Manila clam Ruditapes philippinarum, one of the most dominant bivalves of the estuarine and coastal lagoon environments, for 28 days to unfunctionalized multi-walled carbon nanotube MWCNTs (Nf-MWCNTs) and carboxylated MWCNTs (f-MWCNTs), maintained at control salinity (28) and low salinity 21. Concentration-dependent toxicity was demonstrated in individuals exposed to both MWCNT materials and under both salinities, generating alterations of energy reserves and metabolism, oxidative status and neurotoxicity compared to non-contaminated clams. Moreover, our results showed greater toxic impacts induced in clams exposed to f-MWCNTs compared to Nf-MWCNTs. In the present study it was also demonstrated how salinity shifts altered the toxicity of both MWCNT materials as well as the sensitivity of R. philippinarum exposed to these contaminates in terms of clam metabolism, oxidative status and neurotoxicity.

Effects of single and combined exposure of pharmaceutical drugs (carbamazepine and cetirizine) and a metal (cadmium) on the biochemical responses of R. philippinarum.

In the aquatic environment, organisms are exposed to complex mixtures of contaminants which may alter the toxicity profile of each compound, compared to its toxicity alone. Pharmaceutical drugs (e.g. carbamazepine (CBZ) and cetirizine (CTZ)) and metals (e.g. cadmium (Cd)) are among those contaminants that co-occur in the environment. However, most studies concerning their toxicity towards aquatic species are based on single exposure experiments. Thus, the present study aimed to evaluate single and combined effects of Cd and CBZ or CTZ (single conditions: Cd, CTZ, CBZ; combined conditions: CTZ + Cd, CBZ + Cd) on biomarkers related to oxidative stress and energy metabolism in the edible clam Ruditapes philippinarum, by exposing the organisms for 28 days to environmentally relevant concentrations of these contaminants. The biomarkers studied were: i) the electron transport system activity, protein and glycogen contents (indicators of organisms' metabolic status and energy reserves); ii) lipid peroxidation and the ratio between reduced and oxidized glutathione (indicators of oxidative stress); iii) superoxide dismutase and catalase activities (enzymes indicators of antioxidant defence) and iv) activity of glutathione S-transferases (family of enzymes indicators of biotransformation capacity). Results obtained showed that the uptake of Cd and CBZ was not affected by the combined presence of the contaminants. However, for CTZ, the uptake was higher in the presence than in the absence of Cd. Concerning toxicity data, in general, the combined exposures (CTZ + Cd, CBZ + Cd) had lower biological effects than the contaminants alone. Nevertheless, our data showed that despite the low concentrations tested, they were enough to exert biological effects that differed between single and combined treatments, evidencing the need to conduct more co-exposure studies to increase the environmental relevance of the gathered data.

Purification and characterization of a protease from the visceral mass of Mytella charruana and its evaluation to obtain antimicrobial peptides.

This work describes purification of a protease from the visceral mass of the mussel Mytella charruana as well as evaluation of its ability to hydrolyze milk casein to generate antimicrobial peptides. The enzyme showed pI of 4.1 and a single polypeptide band of 83.1 kDa after SDS-PAGE. Sequence similarities with tropomyosin and myosin from mollusks were detected. The protease showed a trypsin-like activity with optimal temperature of 40 °C and stability in a wide pH range (3.0-9.0). Km was 4.28 ±â€¯0.34 mM of the synthetic substrate N-benzoyl-dl-arginyl-ρ-nitroanilide, whereas Vmax was 0.056 ±â€¯0.001 nmol min-1. The enzyme hydrolyzed casein, and the hydrolysate inhibited the growth of Escherichia coli, Micrococcus luteus, Bacillus subtilis, and Klebsiella pneumoniae at a minimal inhibitory concentration of 5.0 µg mL-1. In conclusion, the visceral mass of M. charruana contains a trypsin-like protease that can generate peptides from casein that have a bacteriostatic effect.

Uptake and metabolism of carbamazepine (CBZ) by clam Ruditapes decussatus and its effects in biochemical responses.

1. Laboratory experiments were carried out to assess uptake and metabolism of the epilepsy drug, carbamazepine and its consequent biological responses in marine clam (Ruditapes decussatus) a model non-target organism in ecotoxicology. 2. Clams were exposed to two nominal concentrations (C1 = 30 µg/L and C2 = 50 µg/L) of CBZ for a maximum period of 14 days. Analysis of CBZ and their metabolites in clam and water after exposure to two nominal concentrations of the pharmaceutical drug were performed using UPLC-HRMS analysis. CBZ accumulation reached an average tissue concentration of 1241.59 ng/g dw and 1664.33 ng/g dw at low and high nominal concentration, respectively. 3. Furthermore, a metabolite (3-hydroxy-CBZ) was detected in tissues indicating carbamazepine translocation and metabolism inside clam, suspect screening of CBZ glucuronides was also performed by accurate mass extraction but it could not be detected. 4. Activities of antioxidant enzymes superoxide dismutase, catalase and gluthatione-S-transferase generally increased. Change in the contents of glutathione, malondialdehyde and protein carbonyl were also studied. 5. Results indicated that the bioaccumulation of CBZ resulted in the changes of the antioxidant defense system and the production of ROS with the oxidative stress, ultimately induced alteration in lipid peroxidation and protein carbonyl.

Carbonic anhydrase 2-like in the giant clam, Tridacna squamosa: characterization, localization, response to light, and possible role in the transport of inorganic carbon from the host to its symbionts.

The fluted giant clam, Tridacna squamosa, lives in symbiosis with zooxanthellae which reside extracellularly inside a tubular system. Zooxanthellae fix inorganic carbon (Ci) during insolation and donate photosynthate to the host. Carbonic anhydrases catalyze the interconversion of CO2 and HCO3-, of which carbonic anhydrase 2 (CA2) is the most ubiquitous and involved in many biological processes. This study aimed to clone a CA2 homolog (CA2-like) from the fleshy and colorful outer mantle as well as the thin and whitish inner mantle of T. squamosa, to determine its cellular and subcellular localization, and to examine the effects of light exposure on its gene and protein expression levels. The cDNA coding sequence of CA2-like from T. squamosa comprised 789 bp, encoding 263 amino acids with an estimated molecular mass of 29.6 kDa. A phenogramic analysis of the deduced CA2-like sequence denoted an animal origin. CA2-like was not detectable in the shell-facing epithelium of the inner mantle adjacent to the extrapallial fluid. Hence, CA2-like is unlikely to participate directly in light-enhanced calcification. By contrast, the outer mantle, which contains the highest density of tertiary tubules and zooxanthellae, displayed high level of CA2-like expression, and CA2-like was localized to the tubule epithelial cells. More importantly, exposure to light induced significant increases in the protein abundance of CA2-like in the outer mantle. Hence, CA2-like could probably take part in the increased supply of inorganic carbon (Ci) from the host clam to the symbiotic zooxanthellae when the latter conduct photosynthesis to fix Ci during light exposure.

Structure-Related Differences between Cytochrome Oxidase I Proteins in a Stable Heteroplasmic Mitochondrial System.

Many bivalve species have two types of mitochondrial DNA passed independently through the female line (F genome) and male line (M genome). Here we study the cytochrome oxidase I protein in such bivalve species and provide evidence for differences between the F and M proteins in amino acid property values, particularly relating to hydrophobicity and helicity. The magnitude of these differences varies between different regions of the protein and the change from the ancestor is most marked in the M protein. The observed changes occur in parallel and in the same direction in the different species studied. Two possible causes are considered, first relaxation of purifying selection with drift and second positive selection. These may operate in different ways in different regions of the protein. Many different amino acid substitutions contribute in a small way to the observed variation, but substitutions involving alanine and serine have a quantitatively large effect. Some of these substitutions are potential targets for phosphorylation and some are close to residues of functional importance in the catalytic mechanism. We propose that the observed changes in the F and M proteins might contribute to functional differences between them relating to ATP production and mitochondrial membrane potential with implications for sperm function.

Molecular characterization, expression and antimicrobial activities of two c-type lysozymes from manila clam Venerupis philippinarum.

Lysozymes play an important role in the innate immune responses with which mollusks respond to bacterial invasion through its lytic activity. In the present study, two c-type lysozymes (designed as VpCLYZ-1 and VpCLYZ-2, respectively) were identified and characterized from the manila clam Venerupis philippinarum. The full-length cDNA of VpCLYZ-1 and VpCLYZ-2 was of 629 and 736 bp, encoding a polypeptide of 156 and153 amino acid residues, respectively. The deduced amino acid sequences of VpCLYZs showed high similarity to other known invertebrate c-type lysozymes. Multiple alignments and phylogenetic relationship strongly suggested that VpCLYZ-1 and VpCLYZ-2 belonged to the c-type lysozyme family. Both VpCLYZ-1 and VpCLYZ-2 transcripts were constitutively expressed in a wide range of tissues with different levels. The VpCLYZ-1 transcript was dominantly expressed in hepatopancreas and hemocytes, while VpCLYZ-2 transcript was mainly expressed in the tissues of hepatopancreas and gills. Both the mRNA expression of VpCLYZ-1 and VpCLYZ-2 was significantly up-regulated at 12 h post Vibrio anguillarum challenge. The recombinant VpCLYZ-1 and VpCLYZ-2 (designed as rVpCLYZ-1 and rVpCLYZ-2) exhibited lytic activity against all tested bacteria, and rVpCLYZ-1 showed higher activities than rVpCLYZ-2 in killing Micrococcus luteus and V. anguillarum. Overall, our results suggested that VpCLYZ-1 and VpCLYZ-2 belonged to the c-type lysozyme family, and played important roles in the immune responses of manila clam, especially in the elimination of pathogens.

Biomarkers of environmental stress in gills of Pinna nobilis (Linnaeus 1758) from Balearic Island.

In aquatic environments, bivalve molluscs are used as sentinel species for environmental biomonitoring. In this study Pinna nobilis specimens, the biggest Mediterranean bivalve, were collected in the Magaluf bay (Mallorca), a touristic location and in a pristine area of the Cabrera National Park as the control location. Histological and histochemical analysis in gills of specimens sampled from Magaluf exhibited evident tissue alterations with high presence of haemocytes. Lower acetylcholinesterase (AChE) activity and protein expression were also found in the gills of specimens collected from Magaluf compared with the control area. The determination of antioxidant enzyme activities, such as superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase, showed a higher activities of these antioxidant enzymes and total glutathione content in samples from Magaluf bay than in Cabrera. In conclusion, the present study demonstrated that human activities result in morphological tissue alterations and a reduced AChE activity in gills of P. nobilis. Moreover, these stressful environmental conditions induced an adaptive response in P. nobilis as evidenced by increased antioxidant defences and a decreased AChE activity. CAPSULE: The human activities induce oxidative stress in P. nobilis as evidenced by increased antioxidant defences and a decreased acetylcholinesterase activity.

Cadmium sulfide quantum dots induce oxidative stress and behavioral impairments in the marine clam Scrobicularia plana.

Cadmium sulfide (CdS) quantum dots have a number of current applications in electronics and solar cells and significant future potential in medicine. The aim of the present study was to examine the toxic effects of CdS quantum dots on the marine clam Scrobicularia plana exposed for 14 d to these nanomaterials (10 µg Cd L(-1) ) in natural seawater and to compare them with soluble Cd. Measurement of labile Cd released from CdS quantum dots showed that 52% of CdS quantum dots remained in the nanoparticulate form. Clams accumulated the same levels of Cd regardless of the form in which it was delivered (soluble Cd vs CdS quantum dots). However, significant changes in biochemical responses were observed in clams exposed to CdS quantum dots compared with soluble Cd. Increased activities of catalase and glutathione-S-transferase were significantly higher in clams exposed in seawater to Cd as the nanoparticulate versus the soluble form, suggesting a specific nano effect. The behavior of S. plana in sediment showed impairments of foot movements only in the case of exposure to CdS quantum dots. The results show that oxidative stress and behavior biomarkers are sensitive predictors of CdS quantum dots toxicity in S. plana. Such responses, appearing well before changes might occur at the population level, demonstrate the usefulness of this model species and type of biomarker in the assessment of nanoparticle contamination in estuarine ecosystems.

Cysteine dioxygenase and cysteine sulfinate decarboxylase genes of the deep-sea mussel Bathymodiolus septemdierum: possible involvement in hypotaurine synthesis and adaptation to hydrogen sulfide.

It has been suggested that invertebrates inhabiting deep-sea hydrothermal vent areas use the sulfinic acid hypotaurine, a precursor of taurine, to protect against the toxicity of hydrogen sulfide contained in the seawater from the vent. In this protective system, hypotaurine is accumulated in the gill, the primary site of sulfide exposure. However, the pathway for hypotaurine synthesis in mollusks has not been identified. In this study, we screened for the mRNAs of enzymes involved in hypotaurine synthesis in the deep-sea mussel Bathymodiolus septemdierum and cloned cDNAs encoding cysteine dioxygenase and cysteine sulfinate decarboxylase. As mRNAs encoding cysteamine dioxygenase and cysteine lyase were not detected, the cysteine sulfinate pathway is suggested to be the major pathway of hypotaurine and taurine synthesis. The two genes were found to be expressed in all the tissues examined, but the gill exhibited the highest expression. The mRNA level in the gill was not significantly changed by exposure to sulfides or thiosulfate. These results suggests that the gill of B. septemdierum maintains high levels of expression of the two genes regardless of ambient sulfide level and accumulates hypotaurine continuously to protect against sudden exposure to high level of sulfide.

Biochemical responses in the gills of Meretrix meretrix after exposure to treated municipal effluent.

The biochemical effects in marine bivalves exposed to increasing concentrations of treated municipal effluent (TME), as discharged into receiving marine waters, are investigated. The effluent was collected from a municipal sewage treatment plant (STP) in Qingdao (China). Meretrix meretrix were exposed to effluent volume ratio (EVR, ratio of effluent volume accounted for tailwater seawater mixture) 0%, 1%, 5%, 10%, and 20% (v/v) TME for 15 days and the following biochemical responses in gills were measured: (1) the activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase (GR), and glutathione (GSH) content, and lipid peroxidation levels of malondialdehyde (MDA), as oxidative stress biomarkers; (2) the activity of 7-ethoxyresorufin O-deethylase (EROD) and gluthathione S-transferase (GST), as phase I and phase II conjugation enzymes, respectively; (3) acetylcholinesterase (AChE), as a biomarker of neurotoxicity, and (4) metallothioneins (MTs), as proteins strongly induced by heavy metals. Most of the biochemical indices present high and significant variation frequency (above 50%). There is enhancement in the antioxidant enzymes, EROD, GST, AChE, and MTs, as well as consumption of GSH. The current experimental results suggest that effluent with concentrations less than 20% (v/v) do not cause lipid peroxidation damage. This implies that the activated defense is sufficient to protect the bivalves' gill tissues from cytotoxicity produced by the effluent. Furthermore, GSH, GPx, MTs, and GR are suitable, and sufficiently sensitive, biomarkers to indicate the pollution levels in marine environments receiving such effluent.

Pierisins and CARP-1: ADP-ribosylation of DNA by ARTCs in butterflies and shellfish.

The cabbage butterfly, Pieris rapae, and related species possess a previously unknown ADP-ribosylating toxin, guanine specific ADP-ribosyltransferase. This enzyme toxin, known as pierisin, consists of enzymatic N-terminal domain and receptor-binding C-terminal domain, or typical AB-toxin structure. Pierisin efficiently transfers an ADP-ribosyl moiety to the N(2) position of the guanine base of dsDNA. Receptors for pierisin are suggested to be the neutral glycosphingolipids, globotriaosylceramide (Gb3), and globotetraosylceramide (Gb4). This DNA-modifying toxin exhibits strong cytotoxicity and induces apoptosis in various human cell lines, which can be blocked by Bcl-2. Pierisin also produces detrimental effects on the eggs and larvae of the non-habitual parasitoids. In contrast, a natural parasitoid of the cabbage butterfly, Cotesia glomerata, was resistant to this toxin. The physiological role of pierisin in the butterfly is suggested to be a defense factor against parasitization by wasps. Other type of DNA ADP-ribosyltransferase is present in certain kinds of edible clams. For example, the CARP-1 protein found in Meretrix lamarckii consists of an enzymatic domain without a possible receptor-binding domain. Pierisin and CARP-1 are almost fully non-homologous at the amino acid sequence level, but other ADP-ribosyltransferases homologous to pierisin are present in different biological species such as eubacterium Streptomyces. Possible diverse physiological roles of the DNA ADP-ribosyltransferases are discussed.

Toxicity of silver nanoparticles and ionic silver: Comparison of adverse effects and potential toxicity mechanisms in the freshwater clam Sphaerium corneum.

A range of studies has addressed possible environmental impacts of nanosilver, but most focused on acute effects in few species. Moreover, it remains unclear if toxic effects are particle-specific or mediated by released silver ions. We investigated chronic effects of nanosilver and soluble silver (AgNO3) on the freshwater bivalve Sphaerium corneum. Animals were exposed to nanosilver (0-500 µg Ag L(-1)) and AgNO3 (0-318 µg Ag L(-1)) over 28 days, and effects on reproduction and behavioral changes were assessed. To explore toxic mechanisms, we evaluated the effects on intracellular levels of reactive oxygen species (ROS) and the activity of antioxidant enzymes (superoxide dismutase, catalase, glutathione-S-transferase, glutathione peroxidase). We further explored the activity of the sodium-potassium adenosine triphosphatase (Na(+)/K(+)-ATPase). Chronic exposure to nanosilver and AgNO3 resulted in negative effects on reproduction at concentrations of 5 and 3.18 µg Ag L(-1) (LOEC), respectively. ROS levels significantly increased after exposure to nanosilver at 10 µg Ag L(-1) and AgNO3 at 63.5 µg Ag L(-1). Both forms of silver altered the activities of antioxidant enzymes. Nanosilver (500 µg Ag L(-1)) and AgNO3 (318 µg Ag L(-1)) inhibited Na(+)/K(+)-ATPase activity by 82.6 and 78.9%, respectively. Nanoparticulate and soluble silver produced similar effects in S. corneum suggesting that toxicity of nanosilver is mainly mediated by dissolution of nanoparticles in the test media or after uptake by the test organisms.

A new barrier to dispersal trapped old genetic clines that escaped the Easter Microplate tension zone of the Pacific vent mussels.

Comparative phylogeography of deep-sea hydrothermal vent species has uncovered several genetic breaks between populations inhabiting northern and southern latitudes of the East Pacific Rise. However, the geographic width and position of genetic clines are variable among species. In this report, we further characterize the position and strength of barriers to gene flow between populations of the deep-sea vent mussel Bathymodiolus thermophilus. Eight allozyme loci and DNA sequences of four nuclear genes were added to previously published sequences of the cytochrome c oxidase subunit I gene. Our data confirm the presence of two barriers to gene flow, one located at the Easter Microplate (between 21°33'S and 31°S) recently described as a hybrid zone, and the second positioned between 7°25'S and 14°S with each affecting different loci. Coalescence analysis indicates a single vicariant event at the origin of divergence between clades for all nuclear loci, although the clines are now spatially discordant. We thus hypothesize that the Easter Microplate barrier has recently been relaxed after a long period of isolation and that some genetic clines have escaped the barrier and moved northward where they have subsequently been trapped by a reinforcing barrier to gene flow between 7°25'S and 14°S.