The effect of lead on the metabolic and energetic status of the Yabby, Cherax destructor, during environmental hypoxia

Dietary melatonin positively impacts the immune system of crayfish, Cherax destructor, as revealed by comparative proteomics analysis

Melatonin, an indoleamine with various biological activities, is being used increasingly in the aquaculture industry for its broad immune effects. Cherax destructor is an emerging economically cultured crayfish that faces many problems in the breeding process. Previous work found that dietary melatonin has positive effects on the growth and immunity of C. destructor, but the specific mechanism involved remained unclear. In this study, proteomics was used to determine the mechanism of action of melatonin in C. destructor. Results showed that dietary melatonin resulted in decreased levels of hydrogen peroxide, alanine aminotransferase, and aspartate aminotransferase, but increased levels of glutathione peroxidase, acid phosphatase, and glutathione S-transferases. In total, 608 proteins were differentially expressed (418 upregulated and 190 downregulated), and were enriched in three main categories: innate immunity (B cell receptor signaling pathway and natural killer cell-mediated cytotoxicity), glucose metabolism (pentose phosphate pathway, pentose and glucuronate interconversions, and propionate metabolism), and amino acid metabolism (valine, leucine, and isoleucine degradation, and cysteine and methionine metabolism). In addition, dietary melatonin was also involved in the regulation of the mTOR signaling pathway, and upregulated the expression of genes encoding key factors, such as Ras-related GTP-binding protein A/B, eukaryotic initiation factor 4E, eukaryotic initiation factor 4E-binding protein, and p70 ribosomal S6 kinase. Overall, this study demonstrates the role of melatonin in the physiological regulation of C. destructor, laying the foundation for the development of melatonin as a feed additive in the aquaculture of this species.

Contamination by Trace Elements and Oxidative Stress in the Skeletal Muscle of Scyliorhinus canicula from the Central Tyrrhenian Sea

Marine pollution, due to the regular discharge of contaminants by various anthropogenic sources, is a growing problem that imposes detrimental influences on natural species. Sharks, because of a diet based on smaller polluted animals, are exposed to the risk of water contamination and the subsequent bioaccumulation and biomagnification. Trace elements are very diffuse water pollutants and able to induce oxidative stress in a variety of marine organisms. However, to date, studies on sharks are rather scarce and often limited to mercury. In this context, the present study aimed to analyze the accumulation of trace elements and their putative correlation with the onset of an oxidative status in the muscle of the lesser spotted dogfish Scyliorhinus canicula, from the Central Mediterranean Sea. Ecotoxicological analysis detected the presence of Pb, As, Cd, Mn, Zn, Ni, Cu, and Fe; no significant differences were observed between sexes, while a negative correlation was found between Pb and animal length. Analysis of oxidative stress markers showed either positive or negative correlation with respect to the presence of trace elements. Lipid peroxidation (TBARS) positively correlated with Zn, Ni, and Fe; SOD enzyme activity negatively correlated with Cu and Ni; LDH was negatively correlated with Fe and positively correlated with Pb. Moreover, positive correlations between the leukocyte count and Mn and Zn, as well as with LDH activity, were also observed. The data suggested that, in sharks, trace elements accumulation may affect oxidant and antioxidant processes with important outcomes for their physiology and health.

A study of Pb2+ induced unfolding and aggregation of arginine kinase from Euphausia superba: kinetics and computational simulation integrating study

Arginine kinase is a crucial phosphagen kinase in invertebrates, which is associated to the environmental stress response, plays a key role in cellular energy metabolism. In this study, we investigated the Pb²⁺-induced inhibition and aggregation of Euphausia superba arginine kinase (ESAK) and found that significantly inactivated ESAK in a dose-dependent manner (IC50 = 0.058 ± 0.002 mM). Spectrofluorimetry results showed that Pb²⁺ induced tertiary structural changes via the internal polarity increased and the non-polarity decreased in ESAK and directly induced ESAK aggregation. The ESAK aggregation process induced by Pb²⁺ occurred with multi-phase kinetics. The addition of osmolytes did not show protective effect on Pb²⁺-induced inactivation of ESAK. The computational molecular dynamics (MD) simulation showed that three Pb²⁺ interrupt the entrance of the active site of ESAK and it could be the reason on the loss of activity of ESAK. Several important residues of ESAK were detected that were importantly contributed the conformation and catalytic function of ESAK. Our study showed that Pb²⁺-induced misfolding of ESAK and the complete loss of activity irreversibly, which cannot be recovered by osmolytes.Communicated by Ramaswamy H. Sarma.

Combined metabolomics and histological analysis of the tissues from cuttlefish Sepia pharaonis exposed to inking stress

Inking is part of a defensive stress response in cephalopods (cuttlefish, squid, and octopus). Some individual cuttlefish (Sepia pharaonis) die after continued stress and inking; however, the physiological effects of cephalopods in response to stress and inking remain unknown. The present study investigated the metabolic profile and discussed the physiological roles of S. pharaonis tissues in response to continuous inking using the ¹H NMR spectroscopy coupled with multivariate data analysis. A total of 50 metabolites, including amino acids, organic osmolytes, nucleotides, energy storage compounds, and obvious tissue-specific metabolites induced by inking stress, were identified in S. pharaonis tissues. Exposure to inking stress had different effects on the levels of the studied metabolites, for example, the levels of isoleucine, trimethylamine-N-oxide, and betaine increased, but those of arginine and ATP decreased in the liver; inosine and lactate were accumulated whereas glutamate and choline were depleted in the gill; the levels of lactate and isoleucine were elevated but those of arginine and glycogen were depleted in the muscle tissue. Furthermore, the corresponding metabolic pathways of the characteristic metabolites indicated major changes in the functions of these metabolites. Histological changes in the studied tissues revealed liver lobule damage immediately after inking, with the presence of disordered epithelial cells and partial cell necrosis in the gill. Our results demonstrated that a combination of metabolomics and histological analyses could provide molecular-level insights for elucidating the defense response of cuttlefish against predators.

Characterization and expression of arginine kinase 2 from Macrobrachium nipponense in response to salinity stress

Salinity is a fundamental environmental factor in aquaculture, and arginine kinase (AK) plays imperative roles in innate immune feedback and stress resistance in invertebrates. In the current study, we cloned a full-length cDNA of arginine kinase 2 (MnAK2, GenBank number, MN149533) in Macrobrachium nipponense and analyzed its function through a salinity challenge using bioinformatic approaches. MnAK2 was expressed at the highest levels in hepatopancreas and muscle. Changes in the expression levels of MnAK2, enzymes involved in innate immunity, antioxidant enzymes, and antioxidant enzyme-related genes, and the glutathione and malondialdehyde contents were investigated after 6-week salinity treatment. The expression of MnAK2 gradually increased as salinity increased, and western blotting showed that MnAK2 was significantly upregulated in the 14 and 22 ppt salinity-treatment groups relative to the control group. The findings indicate that high salinity produces oxidative stress and that salinity below isotonic salinity might improve the antioxidant response in M. nipponense. MnAK2 may play a crucial role in the response to salinity stress in M. nipponense.

Modulation of Crustacean Innate Immune Response by Amino Acids and Their Metabolites: Inferences From Other Species

Aquaculture production of crustaceans (mainly shrimp and crabs) has expanded globally, but disease outbreaks and pathogenic infections have hampered production in the last two decades. As invertebrates, crustaceans lack an adaptive immune system and mainly defend and protect themselves using their innate immune system. The immune system derives energy and metabolites from nutrients, with amino acids constituting one such source. A growing number of studies have shown that amino acids and their metabolites are involved in the activation, synthesis, proliferation, and differentiation of immune cells, as well as in the activation of immune related signaling pathways, reduction of inflammatory response and regulation of oxidative stress. Key enzymes in amino acid metabolism have also been implicated in the regulation of the immune system. Here, we reviewed the role played by amino acids and their metabolites in immune-modulation in crustaceans. Information is inferred from mammals and fish where none exists for crustaceans. Research themes are identified and the relevant research gaps highlighted for further studies.

1H NMR-based metabolomic analysis of cuttlefish, Sepia pharaonis (Ehrenberg, 1831) exposed to hypoxia stresses and post-anoxia recovery

Oxygen deficiency (hypoxia and anoxia) is an emerging concern in estuarine and coastal ecosystems worldwide. Previous studies on Mollusca Cephalopoda have focused on the effects of hypoxia stress on physiological performance and survival, but there are few reports on the molecular mechanism, and the application of metabolomics in cephalopods remains unknown. In this study, a ¹H nuclear magnetic resonance (NMR) based metabolomics approach was applied to investigate the metabolites profiles of Sepia pharaonis (Ehrenberg, 1831) during hypoxia and post-anoxia recovery. The results revealed that obvious tissue-specific metabolic responses were induced by hypoxia stresses. Hypoxia exposure influenced the levels of many metabolites (e.g. BCAAs, lactate, and betaine strongly accumulated in the hepatic tissue while arginine and ATP significantly reduced; lactate and adenosine significantly increased in gills whereas arginine and choline significantly decreased; GABA, taurine and adenosine levels increased in brain but a significant depletion of N-Acetylaspartate and glycogen was found), disturbed energy and amino acid metabolism, and broke the balance of neurotransmitters and osmoregulators. Notably, almost all metabolites returned to pre-exposure levels after acute hypoxia recovery. However, we noted a pronounced depletion of the amino acid pool (arginine, glutamine, and alanine) in hepatic and gills after recovery, as well as organic osmolytes fluctuations (choline, betaine, and taurine). This work highlights the potential of metabolomics methods to elucidate the response of cuttlefish to hypoxia stress, as well as to provide knowledge on metabolic changes in cephalopods under the influences of environmental stress.

Continuous Inking Affects the Biological and Biochemical Responses of Cuttlefish Sepia pharaonis

Several marine mollusks, including cephalopods (cuttlefish, squid, and octopus) and gastropods (e.g., sea hares), can release a colored ink secretion when chased by predators or stimulated. Ink release is part of a defensive response, but the threshold for the biochemical responses caused by stimulation is unknown. The present study aimed to reveal antipredator responses of cuttlefish, such as escaping via inking and/or jetting, and to investigate its biological and biochemical responses to continuous ink release. Results showed that the behavioral responses to continuous ink release mainly manifested as blazing body pattern changes. Cuttlefish escaped from predators covered by jetting/inking and warned the potential threats by displaying a unique body pattern. Moreover, persistent inking in the presence of an overt stimulus caused uncontrollable ink release from the ink duct/anal canal (loss of control). This study first verified the characteristics of the cuttlefish ink solution, prepared a standard curve of ink solution concentrations, and fitted the relationship function between the release frequency and the released ink weight. Biological statistics indicated that cuttlefish has the ability to continuously release ink (releasing ∼90% of the ink from the ink sac) and that the individuals adapted well during the recovery period. However, re-releasing ink would result in "overexploitation" and high mortality. Hexokinase (HK), pyruvate kinase (PK), and superoxide dismutase (SOD) activities, as well as malondialdehyde (MDA) concentration increased or remained stable in different tissues after releasing ink. The expression of heat shock protein 90 and arginine kinase (AK) were upregulated by stimuli in all tissues. Biochemical changes indicated that continuous inking not only consumed considerable energy but also damaged the tissues. In summary, cuttlefish released almost 90% of their ink for active defense against predators, and it took ∼30 days for the ink sac to be refilled, but "overexploitation" resulted in serious physiological damage. These findings will be helpful to further study the defense and ink release mechanisms and to consider animal health and welfare when using cephalopods as experimental animals and for aquaculture practices.

First comprehensive analysis of lysine acetylation in Alvinocaris longirostris from the deep-sea hydrothermal vents

Background

Deep-sea hydrothermal vents are unique chemoautotrophic ecosystems with harsh conditions. Alvinocaris longirostris is one of the dominant crustacean species inhabiting in these extreme environments. It is significant to clarify mechanisms in their adaptation to the vents. Lysine acetylation has been known to play critical roles in the regulation of many cellular processes. However, its function in A. longirostris and even marine invertebrates remains elusive. Our study is the first, to our knowledge, to comprehensively investigate lysine acetylome in A. longirostris.

Results

In total, 501 unique acetylation sites from 206 proteins were identified by combination of affinity enrichment and high-sensitive-massspectrometer. It was revealed that Arg, His and Lys occurred most frequently at the + 1 position downstream of the acetylation sites, which were all alkaline amino acids and positively charged. Functional analysis revealed that the protein acetylation was involved in diverse cellular processes, such as biosynthesis of amino acids, citrate cycle, fatty acid degradation and oxidative phosphorylation. Acetylated proteins were found enriched in mitochondrion and peroxisome, and many stress response related proteins were also discovered to be acetylated, like arginine kinases, heat shock protein 70, and hemocyanins. In the two hemocyanins, nine acetylation sites were identified, among which one acetylation site was unique in A. longirostris when compared with other shallow water shrimps. Further studies are warranted to verify its function.

Conclusion

The lysine acetylome of A. longirostris is investigated for the first time and brings new insights into the regulation function of the lysine acetylation. The results supply abundant resources for exploring the functions of acetylation in A. longirostris and other shrimps.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4745-3) contains supplementary material, which is available to authorized users.

Metabolic responses and arginine kinase expression of juvenile cuttlefish (Sepia pharaonis) under salinity stress

The pharaoh cuttlefish Sepia pharaonis is particularly sensitive to environmental changes in its breeding environment. The breeding of S. pharaonis larvae was carried out in different salinities for 48h, and the changes in survival rate, histological structure, energy metabolism, and anti-oxidative stress parameters were investigated and correlated with arginine kinase (AK) expression changes in muscle and liver tissues. The suitable salinity for larvae cultivation ranged from 24 to 30‰, and the survival rate showed a significant decline at 21‰ salinity. Histological observations of muscle and liver showed that changes in salinity and osmotic pressure had an adverse effect on tissue structure. Measurements of glycogen and lactic acid levels suggested that S. pharaonis could dynamically adjust energy metabolism to provide additional energy under unsuitable salinity. The protein levels and enzyme activities of AK in muscle significantly increased at 21‰ salinity. The results were consistent with prompt replenishment of phosphoarginine stores during salinity stress to maintain a dynamic ATP balance, suggesting that AK plays an important role in the regulation of energy metabolism. This study provides insight into metabolic changes during salinity stress and sheds light on the functional role of AK in S. pharaonis.

Behavioural, physiological and biochemical responses to aquatic hypoxia in the freshwater crayfish, Paranephrops zealandicus

Hypoxia resulting from aquatic eutrophication threatens the population health of the New Zealand freshwater crayfish (koura), Paranephrops zealandicus. An integrated study, combining behavioural, physiological and biochemical approaches, was therefore conducted to characterise the tolerance of this species to hypoxia. When provided with a choice between water flows of high or low dissolved oxygen in short-term laboratory assays, crayfish did not preferentially inhabit waters of higher PO₂. However, when an aerial refuge was provided and dissolved oxygen was progressively decreased, crayfish emersed at a PO₂ of 0.56±0.03kPa, suggesting a relatively high tolerance to hypoxia. Closed-box respirometry delineated a P_crit, the point at which crayfish transition from oxyregulating to oxyconforming, of 6.0kPa. Simultaneous measurement of heart rate showed no changes across the PO₂ range. In response to 6-h exposures to fixed dissolved oxygen levels (normoxia, 19.3kPa; moderate hypoxia, 3.5kPa; and severe hypoxia, 1.7kPa), P. zealandicus showed a haemolymph PO₂ that declined with the magnitude of hypoxia, and while plasma pH declined in severe hypoxia, there were no changes in plasma PCO₂. Plasma glucose concentrations fell, and plasma lactate increased in both hypoxic groups. There were no changes in tissue glucose or lactate concentrations. These data indicate that P. zealandicus is relatively tolerant of hypoxia, and possesses biochemical and physiological mechanisms that facilitate survival during short-term exposures to acute hypoxia. If hypoxia is severe and/or prolonged, then this species is capable of escaping to aerial refugia.

Kinetics for Zinc Ion Induced Sepia Pharaonis Arginine Kinase Inactivation and Aggregation

Arginine kinase is an essential enzyme which is closely related to energy metabolism in marine invertebrates. Arginine kinase provides a significant role in quick response to environmental change and stress. In this study, we simulated a tertiary structure of Sepia pharaonis arginine kinase (SPAK) based on the gene sequence and conducted the molecular dynamics simulations between SPAK and Zn²⁺. Using these results, the Zn²⁺ binding sites were predicted and the initial effect of Zn²⁺ on the SPAK structure was elucidated. Subsequently, the experimental kinetic results were compared with the simulation results. Zn²⁺ markedly inhibited the activity of SPAK in a manner of non-competitive inhibitions for both arginine and ATP. We also found that Zn²⁺ binding to SPAK resulted in tertiary conformational change accompanying with the hydrophobic residues exposure. These changes caused SPAK aggregation directly. We screened two protectants, glycine and proline, which effectively prevented SPAK aggregation and recovered the structure and activity. Overall, our study suggested the inhibitory effect of Zn²⁺ on SPAK and Zn²⁺ can trigger SPAK aggregation after exposing large extent of hydrophobic surface. The protective effects of glycine and proline against Zn²⁺ on SPAK folding were also demonstrated.

Multibiomarker responses in aquatic insect Belostoma elegans (Hemiptera) to organic pollution in freshwater system

The present study analyzes a battery of biomarkers in the water bug Belostoma elegans from a stream polluted with organic matter (OMS), and another one considered as reference site (RS) during spring-summer season (December to March). Biochemical parameters of glucidic, lipidic and oxidative metabolic pathways were analyzed in males and females of this insect. In general, no significant differences were observed in all biomarkers assayed between both sexes, except lactate concentration which was higher in males than in females (p < 0.0006) in the first three months. About carbohydrate metabolism parameters, only pyruvate-kinase showed significant differences between insects collected in both streams (p < 0.05) during December. However, the total lipid content, saturated fatty acid, and mainly triacylglycerol were higher in insects from RS compared to those from OMS (p < 0.002) in all sampled months. Levels of lipoperoxidation, protein oxidation, reduced glutathione and glutathione-S-transferase activity showed no differences between insects collected from both streams. Nevertheless, the significant increase observed in superoxide dismutase and catalase activities (p < 0.004) could be due to the elevated oxidative metabolism in insects from RS compared to those from OMS with lower dissolved oxygen. Regarding those responding parameters, males accounted for the differences between the two sites during the study period. In conclusion, our results support that lipidic energetic reserves and antioxidant enzyme activities in B. elegans could be used as biomarkers of environmental pollution by organic matter.

Influence of CeO2 NPs on biological phosphorus removal and bacterial community shifts in a sequencing batch biofilm reactor with the differential effects of molecular oxygen

The effects of CeO₂ nanoparticles (CeO₂ NPs) on a sequencing batch biofilm reactor (SBBR) with established biological phosphorus (P) removal were investigated from the processes of anaerobic P release and aerobic P uptake. At low concentration (0.1mg/L), no significant impact was observed on total phosphorus (TP) removal after operating for 8h. However, at a concentration of 20mg/L, TP removal efficiency decreased from 83.68% to 55.88% and 16.76% when the CeO₂ NPs were added at the beginning of the anaerobic and aerobic periods, respectively. Further studies illustrated that the inhibition of the specific P release rate was caused by the reversible states of Ce³⁺ and Ce⁴⁺, which inhibited the activity of exopolyphosphatase (PPX) and transformation of poly-β-hydoxyalkanoates (PHA) and glycogen, as well as the uptake of volatile fatty acids (VFAs). The decrease in the specific P uptake rate was mainly attributed to the significantly suppressed energy generation and decreased abundance of Burkholderia caused by excess reactive oxygen species. The removal of chemical oxygen demand (COD) was not influenced by CeO₂ NPs under aerobic conditions, due to the increased abundance of Acetobacter and Acidocella after exposure. The inhibitory effects of CeO₂ NPs with molecular oxygen were reduced after anaerobic exposure due to the enhanced particle size and the presence of Ce³⁺.

Effects of atrazine on growth and sex differentiation, in juveniles of the freshwater crayfish Cherax quadricarinatus

The effect of the herbicide atrazine was assayed in early juveniles of the redclaw crayfish Cherax quadricarinatus. Four cohorts of juveniles (a total of 280 animals) were exposed for 4 wk to each one of three atrazine concentrations (0.1, 0.5 and 2.5mg/L) or a control (0mg/L), from a commercial formulation having 90% of active principle. At the end of the exposure, no significant (p>0.05) differences in either mortality or molting were noted. However, the weight gain and the protein content of abdominal muscle decreased significantly (p<0.05) in the highest atrazine concentration as compared to control, indicating that atrazine acted as a relevant stressor, although at a concentration higher than those reported in the environment. Besides, the proportion of females increased progressively as the atrazine concentration increases, being significantly (p<0.05) higher than that of controls at the highest concentration assayed. Both macroscopic and histological analysis revealed a normal architecture of gonopores and gonads in both control and exposed animals. The obtained results strongly suggest that atrazine could be causing an endocrine disruption on the hormonal system responsible for the sexual differentiation of the studied species, increasing the proportion of female proportion without disturbing the gonad structure.

Kinetics for Cu(2+) induced Sepia pharaonis arginine kinase inactivation and aggregation

Arginine kinase plays an important role in cellular energy metabolism and is closely related to the environmental stress response in marine invertebrates. We studied the Cu(2+)-mediated inhibition and aggregation of Sepia pharaonis arginine kinase (SPAK) and found that Cu(2+) markedly inhibited the SPAK activity along with mixed-type inhibition against the arginine substrate and noncompetitive inhibition against the ATP cofactor. Spectrofluorimetry results showed that Cu(2+) induced a tertiary structure change in SPAK, resulting in exposure of the hydrophobic surface and increased aggregation. Cu(2+)-mediated SPAK aggregation followed first-order kinetics consistent with monophasic and a biphasic processes. Addition of osmolytes, including glycine and proline, effectively blocked SPAK aggregation and restored SPAK activity. Our results demonstrated the effects of Cu(2+) on SPAK catalytic function, conformation, and aggregation, as well as the protective effects of osmolytes on SPAK folding. This study provided important insights into the role of Cu(2+) as a negative effector of the S. pharaonis metabolic enzyme AK and the possible responses of cephalopods to unfavorable environmental conditions.

Effects of cadmium exposure on critical temperatures of aerobic metabolism in eastern oysters Crassostrea virginica (Gmelin, 1791)

Cadmium (Cd) and elevated temperatures are common stressors in estuarine and coastal environments. Elevated temperature can sensitize estuarine organisms to the toxicity of metals such as Cd and vice versa, but the physiological mechanisms of temperature-Cd interactions are not well understood. We tested a hypothesis that interactive effects of elevated temperature and Cd stress involve Cd-induced reduction of the aerobic scope of an organism thereby narrowing the thermal tolerance window of oysters. We determined the effects of prolonged Cd exposure (50 μg Cd l(-1)for 30 days) on the upper critical temperature of aerobic metabolism (assessed by accumulation of anaerobic end products L-alanine, succinate and acetate), cellular energy status (assessed by the tissue levels of adenylates, phosphagen/aphosphagen and glycogen and lipid reserves) and oxidative damage during acute temperature rise (20-36 °C) in the eastern oysters Crassostrea virginica. The upper critical temperature (TcII) was shifted to lower values (from 28 to 24 °C) in Cd-exposed oysters in spring and was lower in both control and Cd-exposed groups in winter (24 and <20 °C, respectively). This indicates a reduction of thermal tolerance of Cd-exposed oysters associated with a decrease of the aerobic scope of the organism and early transition to partial anaerobiosis. Acute warming had no negative effects on tissue energy reserves or parameters of cellular energy status of oysters (except a decrease in adenylate content at the extreme temperature of 36 °C) but led to an increase in oxidative lesions of proteins at extreme temperatures. These data show that transition to partial anaerobiosis (indicated by the accumulation of anaerobic end products) is the most sensitive biomarker of temperature-induced transition to energetically non-sustainable state in oysters, whereas disturbances in the cellular energy status (i.e. decline in adenylate and phosphagen levels) and oxidative stress ensue at considerably higher temperatures, nearing the lethal range. This study indicates that long-term exposure of oysters to environmentally relevant levels of Cd may increase their sensitivity to elevated temperatures during seasonal warming and/or the global climate change in polluted estuaries.

Arginine kinase in the cladoceran Daphnia magna: cDNA sequencing and expression is associated with resistance to toxic Microcystis

Nutrient loading derived from anthropogenic activities into lakes have increased the frequency, severity and duration of toxic cyanobacterial blooms around the world. Although herbivorous zooplankton are generally considered to be unable to control toxic cyanobacteria, populations of some zooplankton, including Daphnia, have been shown to locally adapt to toxic cyanobacteria and suppress cyanobacterial bloom formation. However, little is known about the physiology of zooplankton behind this phenomenon. One possible explanation is that some zooplankton may induce more tolerance by elevating energy production, thereby adding more energy allocation to detoxification expenditure. It is assumed that arginine kinase (AK) serves as a core in temporal and spatial adenosine triphosphate (ATP) buffering in cells with high fluctuating energy requirements. To test this hypothesis, we studied the energetic response of a single Daphnia magna clone exposed to a toxic strain of Microcystis aeruginosa, PCC7806. Arginine kinase of D. magna (Dm-AK) was successfully cloned. An ATP-gua PtransN domain which was described as a guanidine substrate specificity domain and an ATP-gua Ptrans domain which was responsible for binding ATP were both identified in the Dm-AK. Phylogenetic analysis of AKs in a range of arthropod taxa suggested that Dm-AK was as dissimilar to other crustaceans as it was to insects. Dm-AK transcript level and ATP content in the presence of M. aeruginosa were significantly lower than those in the control diet containing only the nutritious chlorophyte, Scenedesmus obliquus, whereas the two parameters in the neonates whose mothers had been previously exposed to M. aeruginosa were significantly higher than those of mothers fed with pure S. obliquus. These findings suggest that Dm-AK might play an essential role in the coupling of energy production and utilization and the tolerance of D. magna to toxic cyanobacteria.

Anthropogenic noise compromises antipredator behaviour in European eels

Increases in noise-generating human activities since the Industrial Revolution have changed the acoustic landscape of many terrestrial and aquatic ecosystems. Anthropogenic noise is now recognized as a major pollutant of international concern, and recent studies have demonstrated impacts on, for instance, hearing thresholds, communication, movement and foraging in a range of species. However, consequences for survival and reproductive success are difficult to ascertain. Using a series of laboratory-based experiments and an open-water test with the same methodology, we show that acoustic disturbance can compromise antipredator behaviour--which directly affects survival likelihood--and explore potential underlying mechanisms. Juvenile European eels (Anguilla anguilla) exposed to additional noise (playback of recordings of ships passing through harbours), rather than control conditions (playback of recordings from the same harbours without ships), performed less well in two simulated predation paradigms. Eels were 50% less likely and 25% slower to startle to an 'ambush predator' and were caught more than twice as quickly by a 'pursuit predator'. Furthermore, eels experiencing additional noise had diminished spatial performance and elevated ventilation and metabolic rates (indicators of stress) compared with control individuals. Our results suggest that acoustic disturbance could have important physiological and behavioural impacts on animals, compromising life-or-death responses.

Metabolic signatures associated with environmental pollution by metals in Doñana National Park using P. clarkii as bioindicator

Bioindicators can reflect the effects of pollutants on their metabolism, being widely used to assess environmental stress. In this sense, the crab Procambarus clarkii has been previously proposed to monitor the contamination in Doñana National Park (southwest Spain) using conventional biomarkers. In this work, a metabolomic approach based on direct infusion mass spectrometry, which allows an easy and quick study of a large number of metabolites in a single run, was used for pollution assessment of this area, considering the biological response of this organism to contamination. In addition, metal accumulation in crab tissues was determined. Thus, the integrated analysis of metabolomic and metallomic data enabled the study of metabolic response of the organism against pollution. Several metabolites were discovered as potential biomarkers of pollution, such as decreased levels of carnosine, alanine, niacinamide, acetoacetate, pantothenic acid, ascorbate, glucose-6-phosphate, arginine, glucose, lactate, phospholipids, and tryglicerides, as well as elevated levels of acetyl carnitine, phosphocholine, choline, and uric acid. In this way, metal-induced toxicity could be related to metabolic impairments, principally oxidative stress, metabolic dysfunction, and dyslipidemia.

Identification and expression analysis of differentially expressed genes from shrimp (Penaeus monodon) in response to low salinity stress

Four suppression subtractive hybridization (SSH) cDNA libraries were constructed to identify differentially expressed salinity stress responsive genes of black tiger shrimp, Penaeus monodon exposed to low (3 ppt) salinity conditions. Forward and reverse SSH cDNA libraries were developed from the gill and gut tissues of shrimp and clones having inserts larger than 300 bp were unidirectionally sequenced. Based on the sequence homology search, the identified genes were categorized for their putative functions related to a wide range of biological roles, such as nucleic acid regulation and replication, immune response, energy and metabolism, cell signaling, cellular process, cytoskeleton and membrane structure, stress and osmoregulation. Gene expression levels in response to low salinity conditions at 2 weeks post salinity stress of thirteen selected differentially expressed genes identified from SSH cDNA libraries (14-3-3 like protein, crust in, lysozyme, arginine kinase, Naþ/Kþ-ATPase a-subunit, intracellular fatty acid binding protein, cathepsin B, anti-lipopolysaccharide factor, ferritin, ubiquitin conjugating enzyme E2, calreticulin, innexin 2 and heat shock protein 21) were analyzed by RT-PCR. The highest gene expression levels were observed for Naþ/Kþ-ATPase a-subunit (34.28-folds) in gill tissues, intracellular fatty acid binding protein (13.30-folds) in gut tissues and innexin 2 (14.43-folds) in muscle tissues respectively. The differential and significant levels of gene expression indicate the functional role of these genes in shrimp salinity stress adaptive mechanisms.

A cellular and metabolic assessment of the thermal stress responses in the endemic gastropod Benedictia limnaeoides ongurensis from Lake Baikal

Our objective was to determine if the Lake Baikal endemic gastropod Benedictia limnaeoides ongurensis, which inhabits in stable cold waters expresses a thermal stress response. We hypothesized that the evolution of this species in the stable cold waters of Lake Baikal resulted in a reduction of its thermal stress-response mechanisms at the biochemical and cellular levels. Contrary to our hypothesis, our results show that exposure to a thermal challenge activates the cellular and biochemical mechanisms of thermal resistance, such as heat shock proteins and antioxidative enzymes, and alters energetic metabolism in B. limnaeoides ongurensis. Thermal stress caused the elevation of heat shock protein 70 and the products of anaerobic glycolysis together with the depletion of glucose and phosphagens in the studied species. Thus, a temperature increase activates the complex biochemical system of stress response and alters the energetic metabolism in this endemic Baikal gastropod. It is concluded that the deepwater Lake Baikal endemic gastropod B. limnaeoides ongurensis retains the ability to activate well-developed biochemical stress-response mechanisms when exposed to a thermal challenge.

Relative importance of direct and trophic uranium exposures in the crayfish Orconectes limosus: Implication for predicting uranium bioaccumulation and its associated toxicity

Pollutants that occur at sublethal concentrations in the environment may lead to chronic exposure in aquatic organisms. If these pollutants bioaccumulate, then organisms higher in the food chain may also be at risk. Increased attention has thus been focused on the relative importance of dietary uptake, but additional knowledge of the cellular distribution of metals after dietary exposure is required to assess the potential toxicity. The authors address concerns relating to increasing uranium (U) concentrations (from 12 µg/L to 2 mg/L) in the freshwater ecosystem caused by anthropogenic activities. The objective of the present study is to compare uranium bioaccumulation levels in tissues and in the subcellular environment. The authors focused on the cytosol fraction and its microlocalization (TEM-EDX) in the gills and the hepatopancreas (HP) of the crayfish Orconectes limosus after 10 d of direct exposure (at concentrations of 20, 100, and 500 µg/L) and five trophic exposure treatments (at concentrations from 1 to 20 µg/g). Results indicated that adsorption of uranium on the cuticle represents the main contribution of total uranium accumulation to the animal. Accumulation in the gills should be considered only as a marker of waterborne uranium exposure. Accumulation in the HP after trophic environmental exposure conditions was higher (18.9 ± 3.8 µg/g) than after direct exposure. Moreover, no significant difference in the subcellular distribution of uranium (50%) in HP was observed between animals that had been exposed to both types of treatment. A potential toxic effect after uranium accumulation could therefore exist after trophic exposure. This confirms the need to focus further studies on the metal (uranium) risk assessment.

Impact of Cr(VI) on P removal performance in enhanced biological phosphorus removal (EBPR) system based on the anaerobic and aerobic metabolism

Influence of Cr(VI) on P removal in enhanced biological phosphorus removal (EBPR) system was investigated with respect to the composition of poly-phosphate-accumulating organisms (PAOs) and glycogen accumulating organisms (GAOs), the transformation of poly-β-hydroxyalkanoates (PHA) and glycogen, enzymes' activities, and the intracellular Cr. Whether EBPR system could revive after Cr(VI) shock was also explored. Results showed P removal performance was completely inhibited by Cr(VI) with the concentration more than 5 mg L(-1). PAOs were more sensitive to Cr(VI) than GAOs and the other bacteria were. PHA consumption, glycogen synthesis and adenylate kinase's activity had been inhibited by 5 mg L(-1) Cr(VI). Both adenylate kinase's activity and P removal efficiency were negatively correlated with the intracellular Cr. Recovery experiments revealed that P removal performance with 5 mg L(-1) Cr(VI) shock could revive after a 2-day recovery treatment, while systems with high level Cr(VI) (20 and 60 mg L(-1)) shock could not.

Exposure-dose-response of Anadara trapezia to metal contaminated estuarine sediments. 2. Lead spiked sediments

The composition of near shore marine environments is increasingly being altered by contaminants from human activities. The ability of lead, which has no known biological function, to mimic biologically essential metals makes it one of the most toxic to marine biota. The relationship between lead exposure, dose and response was investigated in Anadara trapezia exposed for 56 days to lead spiked sediment (100 and 300 μg/g dry mass). Lead tissue concentrations of the 300 μg/g exposed A. trapezia doubled in the last 2 weeks of exposure with final lead tissue concentrations of exposed organisms of 1 and 12 μg/g, respectively. Tissue lead accumulation of exposed organisms followed the pattern haemolymph>gill>hepatopancreas during much of the 56 day exposure. Between 30 and 69% of accumulated lead in the gill and hepatopancreas was detoxified and fairly evenly distributed between the metal rich granule and the metallothionein like protein fractions. Approximately half of the biologically active lead in both tissues was in the mitochondrial fraction which showed increased cytochrome c oxidase activity in lead exposed organisms. There was a reduction in GPx activity, an associated increase in total glutathione concentrations and reduced GSH:GSSG ratios due to a build up of oxidised glutathione. These changes in the glutathione pathway were reflected in the total antioxidant capacity of lead exposed A. trapezia which were significantly reduced compared to control organisms. Increased lead exposure significantly increased lipid peroxidation, lysosomal destabilisation and frequency of micronuclei. A significant exposure-dose-response relationship for A. trapezia exposed to lead enriched sediments indicates that elevated sediment lead concentrations have the potential to increase biologically active lead burdens and impair the antioxidant reduction capacity leading to a series of associated effects from lipid peroxidation to cellular perturbation and genotoxic damage.

The function of mitochondrial F(O)F(1) ATP-synthase from the whiteleg shrimp Litopenaeus vannamei muscle during hypoxia

The effect of hypoxia and re-oxygenation on the mitochondrial complex F(O)F(1)-ATP synthase was investigated in the whiteleg shrimp Litopenaeus vannamei. A 660 kDa protein complex isolated from mitochondria of the shrimp muscle was identified as the ATP synthase complex. After 10h at hypoxia (1.5-2.0 mg oxygen/L), the concentration of L-lactate in plasma increased significantly, but the ATP amount and the concentration of ATPβ protein remained unaffected. Nevertheless, an increase of 70% in the ATPase activity was detected, suggesting that the enzyme may be regulated at a post-translational level. Thus, during hypoxia shrimp are able to maintain ATP amounts probably by using some other energy sources as phosphoarginine when an acute lack of energy occurs. During re-oxygenation, the ATPase activity decreased significantly and the ATP production continued via the electron transport chain and oxidative phosphorylation. The results obtained showed that shrimp faces hypoxia partially by hydrolyzing the ATP through the reaction catalyzed by the mitochondrial ATPase which increases its activity.

Cloning and expression of arginine kinase from a swimming crab, Portunus trituberculatus

Arginine kinase (AK) is an important phosphotransferase that plays a critical role in energy metabolism in invertebrates. In this paper, the cDNA of AK (designated as PtAK) was identified from the eyestalk cDNA library of swimming crab Portunus trituberculatus. The full-length cDNA was 1,479 bp, containing an open reading frame of 1,074 bp that coded for 357 amino acids. The estimated molecular mass of mature PtAK was 40.30 kDa and theoretical isoelectric point was 6.18. Amino acid sequence alignment showed that PtAK had very high similarity with other shrimp and crab AKs ranging from 0.876 to 0.983. The genomic DNA fragments of about 1,434 bp consisted of two exons interrupted by an intron. Totally 24 SNPs, including 17 in the coding region and seven in the non-coding region, were detected by direct sequencing of 19 genomic samples. In exon 1, the coding SNPs (cSNPs) were only found in the disease-resistant specimens. The fluorescent real-time PCR analysis revealed that the expression of PtAK was detected in all the examined tissues with the highest expression in the muscle and the lowest in the eyestalk. The expression of PtAK after Vibrio alginolyticus injection was tested in haemocytes, showing that two peak values were 5.01-fold (at 3 h) and 3.60-fold (at 24 h) compared with the control values, respectively. The results suggested that AK might play an important role in the immune response in crabs.

Gene profiling and characterization of arginine kinase-1 (MrAK-1) from freshwater giant prawn (Macrobrachium rosenbergii)

Arginine kinase-1 (MrAK-1) was sequenced from the freshwater prawn Macrobrachium rosenbergii using Illumina Solexa Genome Analyzer Technique. MrAK-1 consisted of 1068 bp nucleotide encoded 355 polypeptide with an estimated molecular mass of 40 kDa. MrAK-1 sequence contains a potential ATP:guanido phosphotransferases active domain site. The deduced amino acid sequence of MrAK-1 was compared with other 7 homologous arginine kinase (AK) and showed the highest identity (96%) with AK-1 from cherry shrimp Neocaridina denticulate. The qRT-PCR analysis revealed a broad expression of MrAK-1 with the highest expression in the muscle and the lowest in the eyestalk. The expression of MrAK-1 after challenge with the infectious hypodermal and hematopoietic necrosis virus (IHHNV) was tested in muscle. In addition, MrAK-1 was expressed in Escherichia coli by prokaryotic expression plasmid pMAL-c2x. The optimum temperature (30 °C) and pH (8.5) was determined for the enzyme activity assay. MrAK-1 showed significant (P < 0.05) activity towards 10-50 mM ATP concentration. The enzyme activity was inhibited by α-ketoglutarate, glucose and ATP at the concentration of 10, 50 and 100 mM respectively. Conclusively, the findings of this study indicated that MrAK-1 might play an important role in the coupling of energy production and utilization and the immune response in shrimps.

Catalytic subunits atpα and atpβ from the Pacific white shrimp Litopenaeus vannamei F(O)F (1) ATP-synthase complex: cDNA sequences, phylogenies, and mRNA quantification during hypoxia

In the mitochondrial F(O)F(1) ATP-synthase/ATPase complex, subunits α and β are part of the extrinsic portion that catalyses ATP synthesis. Since there are no reports about genes and proteins from these subunits in crustaceans, we analyzed the cDNA sequences of both subunits in the whiteleg shrimp Litopenaeus vannamei and their phylogenetic relationships. We also investigated the effect of hypoxia on shrimp by measuring changes in the mRNA amounts of atpα and atpβ. Our results confirmed highly conserved regions for both subunits and underlined unique features among others. The ATPβ deduced protein of shrimp was less conserved in size and sequence than ATPα. The relative mRNA amounts of atpα and atpβ changed in shrimp pleopods; hypoxia at 1.5 mg/L caused an increase in atpβ transcripts and a subsequent decrease when shrimp were re-oxygenated. Results confirm that changes in the mRNAs of the ATP-synthase subunits are part of the mechanisms allowing shrimp to deal with the metabolic adjustment displayed to tolerate hypoxia.

Energy metabolism and metabolic depression during exercise in Callinectes sapidus, the Atlantic blue crab: effects of the bacterial pathogen Vibrio campbellii

Callinectes sapidus (Rathbun), the Atlantic blue crab, commonly harbors low to moderate amounts of bacteria in hemolymph and other tissues. These bacteria are typically dominated by Vibrio spp., which are known to cause mortality in the blue crab. The dose-dependent lethality of an isolate of Vibrio campbellii was determined in crabs; the mean 48 h LD50 (half-maximal lethal dose) was 6.2×105 colony forming units g–1 crab. Injection of a sublethal dose of V. campbellii into the hemolymph of the crab resulted in a rapid and large depression (30–42%) of metabolic rate, which persisted for 24 h. Because gills are an organ of immune function as well as respiration, we were interested in how bacteria injected into the crab would affect the energetic costs associated with walking. Overall metabolism (aerobic and anaerobic) more than doubled in crabs walking for 30 min at 8 m min–1. The metabolic depression resulting from bacterial injection persisted throughout the exercise period and patterns of phosphagen and adenylate consumption within walking leg muscle were not affected by treatment. The ability of crabs to supply required energy for walking is largely unaffected by exposure to Vibrio; however, Vibrio-injected crabs are less aerobic while doing so. This depressed metabolic condition in response to bacteria,present during moderate activity, could be a passive result of mounting an immune response or may indicate an actively regulated metabolic depression. A compromised metabolism can affect the performance of daily activities, such as feeding and predator avoidance or affect the ability to cope with environmental stressors, such as hypoxia.

Cadmium affects metabolic responses to prolonged anoxia and reoxygenation in eastern oysters (Crassostrea virginica)

Benthic marine organisms such as mollusks are often exposed to periodic oxygen deficiency (due to the tidal exposure and/or seasonal expansion of the oxygen-deficient dead zones) and pollution by metals [e.g., cadmium, (Cd)]. These stressors can strongly affect mollusks' survival; however, physiological mechanisms of their combined effects are not fully understood. We studied the effects of Cd exposure on metabolic responses to prolonged anoxia and subsequent recovery in anoxia-tolerant intertidal mollusks Crassostrea virginica (eastern oysters). Anoxia led to an onset of anaerobiosis indicated by accumulation of l-alanine, acetate, and succinate. Prolonged anoxia (for 6 days) caused a decline in the maximum activity of electron transport chain and ADP-stimulated ( state 3) oxygen uptake by mitochondria (MO2), but no change in the resting ( state 4) MO2 of oyster mitochondria, along with a slight but significant reduction of mitochondrial respiratory control ratio. During reoxygenation, there was a significant overshoot of mitochondrial MO2 (by up to 70% above the normoxic steady-state values) in control oysters. Mild mitochondrial uncoupling during prolonged shutdown in anoxic tissues and a subsequent strong stimulation of mitochondrial flux during recovery may help to rapidly restore redox status and protect against elevated reactive oxygen species formation in oysters. Exposure to Cd inhibits anaerobic metabolism, abolishes reoxygenation-induced stimulation of mitochondrial MO2, and leads to oxidative stress (indicated by accumulation of DNA lesions) and a loss of mitochondrial capacity during postanoxic recovery. This may result in increased sensitivity to intermittent hypoxia and anoxia in Cd-exposed mollusks and will have implications for their survival in polluted estuaries and coastal zones.

Bioaccumulation of lead nitrate in freshwater crayfish (Astacus leptodactylus) tissues under aquaculture conditions

The aim of this research was to evaluate the amount of lead in the tissue of Astacus leptodactylus especially in their muscle which the consumed part of their body. In this study the crayfish was exposed to intermediate concentration of lead nitrate (500 microg L(-1)) for periods up to 3 weeks. In the first, second and third weeks bioaccumulation in various tissues was under investigation. The data of toxicological analysis obtained by the method of atomic absorption revealed that the levels of bioaccumulation of metal are different in various tissues of this crayfish. The accumulation of the lead in gills was the highest and in muscles was lowest degree. The amount of heavy metals in the tissues of crayfish was as follow. Gills>exoskeleton>hepatopancreas (digestive glands)>digestive tract>green gland>testis and ovary>muscles.