A proteomic analysis of the effects of metal contamination on Sydney Rock Oyster (Saccostrea glomerata) haemolymph

Cadmium Exposure Affects Serum Metabolites and Proteins in the Male Guizhou Black Goat

Food safety and environmental pollution are the hotspots of general concern globally. Notably, long-term accumulation of trace toxic heavy metals, such as cadmium (Cd), in animals may endanger human health via the food chain. The mechanism of Cd toxicity in the goat, a popular farmed animal, has not been extensively investigated to date. Therefore, in this study, ten male goats (Nubian black goat × native black goat) were exposed to Cd via drinking water containing CdCl2 (20 mg Cd·kg-1·BW) for 30 days (five male goats per group). In this study, we used an integrated approach combining proteomics and metabolomics to profile proteins and metabolites in the serum of Cd-exposed goats. It was found that Cd exposure impacted the levels of 30 serum metabolites and 108 proteins. The combined proteomic and metabolomic analysis revealed that Cd exposure affected arginine and proline metabolism, beta-alanine metabolism, and glutathione metabolism. Further, antioxidant capacity in the serum of goats exposed to Cd was reduced. We identified CKM and spermidine as potential protein and metabolic markers, respectively, of early Cd toxicity in the goat. This study details approaches for the early diagnosis and prevention of Cd-poisoned goats.

Effects of chronic exposure to cadmium and copper on the proteome profile of hemolymph in false widow spider Steatoda grossa (Theridiidae)

The aim of this study was to evaluate the quantitative and qualitative changes in the proteome of the hemolymph of female Steatoda grossa spiders (Theridiidae) that were chronically exposed to cadmium and copper in food and were additionally immunostimulated (phorbol 12-myristate 13-acetate (PMA); bacterial suspensions: Staphylococcus aureus (G+), Pseudomonas fluorescens (G-). It was found that the expression of nearly 90 proteins was altered in cadmium-intoxicated spiders and more than 60 in copper-exposed individuals. Regardless of the type of metal used, these proteins were mainly overexpressed in the hemolymph of the exposed spiders. On the other hand, immunostimulation did not significantly change the number of proteins with altered expression in metal-intoxicated individuals. Hemocyanin (Hc) was found to be the most abundant of the proteins identified with altered expression. In copper-intoxicated spiders, immunostimulation increased the expression of A-, E-, F-, and G-chain-containing proteins, while in the case of cadmium-intoxicates spiders, it decreased the expression of E- and A-chain-containing Hc and increased the expression of G-chain-containing Hc. Regardless of the type of metal and immunostimulant used, there was an increase in the expression of actin. In addition, cadmium increased the expression of cullin, vimentin, and ceruloplasmin. The changes observed in the expression of hemolymph proteins indicate their protective function in S. grossa (Theridiidae) spiders under conditions of metal exposure.

Effect of temperature on the toxicokinetics and gene expression of the pacific cupped oyster Crassostrea gigas exposed to cadmium

In this study, we investigated the influence of temperature on the bioaccumulation and depuration of Crassostrea gigas exposed to Cd associated with its molecular responses. Oysters were acclimatized to different temperatures (10 °C, 15 °C, 20 °C, 25 °C, and 30 °C) for 14 d and then exposed to 10 μg/L Cd for 28 d, followed by a depuration period of 35 d. Oysters were sampled for chemical analysis by inductively coupled plasma mass spectrometry (ICP-MS) and for mRNA quantification by qPCR. In the digestive gland, gill, and mantle, the cadmium concentration at 10 °C was significantly lower than that at 25 °C and 30 °C in both the whole experiments. The use of a two-compartment model showed that the uptake rate k₁ in the above three tissues increased with increasing temperatures ranging from 15 to 25 °C. The fastest elimination rates and shortest half-lives were observed at 15-25 °C. The induction of metallothionein (MT) only occurred in the digestive gland at 15 °C and 20 °C at the end of the accumulation phase. In the mantle and gills, the expression of P-glycoprotein (P-gp) was significantly induced at the end of the accumulation phase and significantly inhibited at the end of the depuration phase. In the digestive gland, the expression of P-gp was induced at the end of both the accumulation and depuration phases. Heat shock protein (hsp70) expression exhibited an overall increasing trend throughout the experiment.

Shotgun analysis to identify differences in protein expression between granulocytes and hyalinocytes of the European flat oyster Ostrea edulis

Recovery of wild populations of the European flat oyster Ostrea edulis is important for ecosystem health and conservation of this species, because native oyster populations have dramatically declined or disappeared in most European waters. Diseases have contributed to oyster decline and are important constrains for oyster recovery. Understanding oyster immune system should contribute to design effective strategies to fight oyster diseases. Haemocytes play a pivotal role in mollusc immune responses protecting from infection. Two main types of haemocytes, granulocytes and hyalinocytes, are distinguished in O. edulis. A study aiming to explore differential functions between both haemocyte types and, thus, to enrich the knowledge of Ostrea edulis immune system, was performed by comparing the proteome of the two haemolymph cell types, using a shotgun approach through liquid chromatography (LC) coupled to mass spectrometry (MS). Cells from oyster haemolymph were differentially separated by Percoll density gradient centrifugation. Shotgun LC-MS/MS performance allowed the identification of 145 proteins in hyalinocytes and 138 in the proteome of granulocytes. After a comparative analysis, 55 proteins with main roles in defence were identified, from which 28 were representative of granulocytes and 27 of hyalinocytes, plus 11 proteins shared by both cell types. Different proteins involved in signal transduction, apoptosis, oxidative response, processes related with the cytoskeleton and structure, recognition and wound healing were identified as representatives of each haemocyte type. Important signalling pathways in the immune response such as MAPK, Ras and NF-κβ seemed to be more relevant for granulocytes, while the Wnt signalling pathway, particularly relevant for wound healing, more relevant in hyalinocytes. The differences in proteins involved in recognition and in cytoskeleton and structure suggest differential specialisation in processes of phagocytosis and internalisation of pathogens between haemocyte types. Apoptosis seemed more active in granulocytes. The differences in proteins involved in oxidative response also suggest different redox processes in each cell type.

The phosphoproteome of rice leaves responds to water and nitrogen supply

The scarcity of freshwater is an increasing concern in flood-irrigated rice, whilst excessive use of nitrogen fertilizers is costly and contributes to environmental pollution. To co-ordinate growth adaptation under prolonged exposure to limited water or excess nitrogen supply, plants employ complex systems for signalling and regulation of metabolic processes. There is limited information on the involvement of one of the most important post-translational modifications (PTMs), protein phosphorylation, in plant adaptation to long-term changes in resource supply. Oryza sativa cv. Nipponbare was grown under two regimes of nitrogen from the time of germination to final harvest. Twenty-five days after germination, water was withheld from half the pots in each nitrogen treatment and low water supply continued for an additional 26 days, while the remaining pots were well watered. Leaves from all four groups of plants were harvested after 51 days in order to test whether phosphorylation of leaf proteins responded to prior abiotic stress events. The dominant impact of these resources is exerted in leaves, where PTMs have been predicted to occur. Proteins were extracted and phosphopeptides were analysed by nanoLC-MS/MS analysis, coupled with label-free quantitation. Water and nitrogen regimes triggered extensive changes in phosphorylation of proteins involved in membrane transport, such as the aquaporin OsPIP2-6, a water channel protein. Our study reveals phosphorylation of several peptides belonging to proteins involved in RNA-processing and carbohydrate metabolism, suggesting that phosphorylation events regulate the signalling cascades that are required to optimize plant response to resource supply.

Effect of Different Species of Prorocentrum Genus on the Japanese Oyster Crassostrea gigas Proteomic Profile

This paper assesses the effects of exposure to toxic concentrations (1200 to 6000 cells/mL) of the dinoflagellates Prorocentrum lima, Prorocentrum minimum, and Prorocentrum rhathymum and several concentrations of aqueous and organic extracts obtained from the same species (0 to 20 parts per thousand) on the Crassostrea gigas (5-7 mm) proteomic profile. Through comparative proteomic map analyses, several protein spots were detected with different expression levels, of which eight were selected to be identified by liquid chromatography-mass spectrometry (LC-MS/MS) analyses. The proteomic response suggests that, after 72 h of exposure to whole cells, the biological functions of C. gigas affected proteins in the immune system, stress response, contractile systems and cytoskeletal activities. The exposure to organic and aqueous extracts mainly showed effects on protein expressions in muscle contraction and cytoskeleton morphology. These results enrich the knowledge on early bivalve developmental stages. Therefore, they may be considered a solid base for new bioassays and/or generation of specific analytical tools that allow for some of the main effects of algal proliferation phenomena on bivalve mollusk development to be monitored, characterized and elucidated.

Hemolymph proteins: An overview across marine arthropods and molluscs

In this compilation we collect information about the main protein components in hemolymph and stress the continued interest in their study. The reasons for such an attention span several areas of biological, veterinarian and medical applications: from the notions for better dealing with the species - belonging to phylum Arthropoda, subphylum Crustacea, and to phylum Mollusca - of economic interest, to the development of 'marine drugs' from the peptides that, in invertebrates, act as antimicrobial, antifungal, antiprotozoal, and/or antiviral agents. Overall, the topic most often on focus is that of innate immunity operated by classes of pattern-recognition proteins. SIGNIFICANCE: The immune response in invertebrates relies on innate rather than on adaptive/acquired effectors. At a difference from the soluble and membrane-bound immunoglobulins and receptors in vertebrates, the antimicrobial, antifungal, antiprotozoal and/or antiviral agents in invertebrates interact with non-self material by targeting some common (rather than some highly specific) structural motifs. Developing this paradigm into (semi) synthetic pharmaceuticals, possibly optimized through the modeling opportunities offered by computational biochemistry, is one of the lessons today's science may learn from the study of marine invertebrates, and specifically of the proteins and peptides in their hemolymph.

Bioenergetics in environmental adaptation and stress tolerance of aquatic ectotherms: linking physiology and ecology in a multi-stressor landscape

Energy metabolism (encompassing energy assimilation, conversion and utilization) plays a central role in all life processes and serves as a link between the organismal physiology, behavior and ecology. Metabolic rates define the physiological and life-history performance of an organism, have direct implications for Darwinian fitness, and affect ecologically relevant traits such as the trophic relationships, productivity and ecosystem engineering functions. Natural environmental variability and anthropogenic changes expose aquatic ectotherms to multiple stressors that can strongly affect their energy metabolism and thereby modify the energy fluxes within an organism and in the ecosystem. This Review focuses on the role of bioenergetic disturbances and metabolic adjustments in responses to multiple stressors (especially the general cellular stress response), provides examples of the effects of multiple stressors on energy intake, assimilation, conversion and expenditure, and discusses the conceptual and quantitative approaches to identify and mechanistically explain the energy trade-offs in multiple stressor scenarios, and link the cellular and organismal bioenergetics with fitness, productivity and/or ecological functions of aquatic ectotherms.

Assessment of trace elements pollution in the sea ports of New South Wales (NSW), Australia using oysters as bioindicators

In this study Sydney rock oysters (S. glomerata) from six major sea ports of NSW, Australia were used as bioindicators to assess the distribution and levels of trace element accumulation in the ports. Substantial enrichment of Cu, Pb and Zn in the oysters of the sea ports were detected when compared to their background samples and the US Environmental Protection Agency (USEPA) provisional tolerable intake standard. Enrichment of As, Al, Fe, Mn, Br, Sr were also found in the oysters at the port areas. The bioconcentration ratios of the trace elements illustrated significant Fe, Cu, Zn, As, Mn, Al, Pb and Cr accumulation in S. glomerate. The biota sediment accumulation factor suggested Cu, Mn and Zn accumulation at two of the ports (Port Yamba and Botany), indicating availability of these metals in the oysters as strong metal accumulators. In addition, integrated metal contamination illustrated notable Fe, Zn, Cu and Al contamination at port environment, whereas cluster analysis portrayed interconnection between the contaminants and the study sites.

iTRAQ-based quantitative proteomic analysis identified Eno1 as a cadmium stress response gene in Propsilocerus akamusi (Tokunaga) hemolymph

Propsilocerus akamusi (Tokunaga) is a common species of midge in Siberia, Japan, and China and an important prey species for fish and aquatic birds. Furthermore, this species has been shown to have an extraordinary capacity to resist cadmium (Cd) toxicity. In this study, isobaric tags for relative and absolute quantitation (iTRAQ) coupled liquid chromatography tandem mass spectrometry (LC-MS/MS) was used to analyze relative changes in the P. akamusi hemolymph proteome following exposure to a sublethal concentration of Cd²⁺. The results showed that Cd²⁺ stress affects energy metabolism in P. akamusi. After examining the differentially expressed proteins (DEPs), only one up-regulated protein associated with metabolism, α-enolase (Eno1) was identified and further isolated and characterized. Sequence alignments showed that the deduced P. akamusi Eno1 amino acid sequence is highly conserved, with similarities of 77-95% noted when compared to other Dipteran Eno1 sequences. Furthermore, prolonged Cd²⁺ exposure impacted Eno1 transcription, protein expression and enzyme activity levels. These results suggest that Eno1 may play a role in the response to Cd²⁺ stress in P. akamusi.

Cholinesterase activity in the cup oyster Saccostrea sp. exposed to chlorpyrifos, imidacloprid, cadmium and copper

In the present study, the sensitivity and concentration dependence of three functionally-defined components of cholinesterase activity (total: T-ChE; eserine-sensitive: Es-ChE; and eserine-resistant: Er-ChE) were quantified in the gill, digestive gland and adductor muscle of the tropical cup oyster Saccostrea sp., following acute (96h) aqueous exposure to commercial formulations of the organophosphate (OP) insecticide chlorpyrifos and the neonicotinoid (NN) imidacloprid (concentration range: 0.1-100mg/L), as well as to dissolved cadmium and copper (concentration range: 1-1000μg/L). Oysters (1.5-5.0cm shell length), field-collected from a boating marina in Santa Marta, Colombia (Caribbean Sea) were exposed in the laboratory to each substance at five concentrations. T-ChE, Es-ChE, and Er-ChE activity were quantified in the three tissues in pools of 5 individuals (3 replicates per concentration), before and after inhibition with the total cholinesterase inhibitor eserine (physostigmine, 100µM). Oysters exposed to chlorpyrifos, imidacloprid and Cd showed reduced T-ChE and Es-ChE activity in gills at highest exposure concentrations, with Es-ChE activity being inhibited proportionally more so than T-ChE, whereas Er-ChE activity showed no significant concentration-response. Digestive gland also showed diminished T-ChE, Es-ChE and Er-ChE activity for highest chlorpyrifos and Cd concentrations relative to controls, but an increase of T-ChE and Er-ChE activity at the highest imidacloprid concentration (100mg/L). For Cu, T-ChE, Es-ChE and Er-ChE activities in gills and digestive gland were elevated relative to controls in oysters exposed to Cu concentrations > 100µg/L. In adductor muscle, T-ChE, Es-ChE and Er-ChE activity showed no apparent pattern for any of the four xenobiotics and concentration levels tested. Although this study confirms acute (96h) concentration-dependent reduction of tissue T-ChE and Es-ChE activity in gills and digestive glands of Saccostrea sp. exposed to high concentrations of chlorpyrifos (100mg/L), significant changes in T-ChE, Es-ChE and Er-ChE were also caused by exposure to Cd and Cu at concentrations > 100µg/L and by exposure to imidacloprid (100mg/L), indicating that cholinesterase activity is not a specific biomarker of organophosphate exposure in this species, but, rather, a biomarker of diverse xenobiotic exposure.

Cadmium effects on DNA and protein metabolism in oyster (Crassostrea gigas) revealed by proteomic analyses

Marine molluscs, including oysters, can concentrate high levels of cadmium (Cd) in their soft tissues, but the molecular mechanisms of Cd toxicity remain speculative. In this study, Pacific oysters (Crassostrea gigas) were exposed to Cd for 9 days and their gills were subjected to proteomic analysis, which were further confirmed with transcriptomic analysis. A total of 4,964 proteins was quantified and 515 differentially expressed proteins were identified in response to Cd exposure. Gene Ontology enrichment analysis revealed that excess Cd affected the DNA and protein metabolism. Specifically, Cd toxicity resulted in the inhibition of DNA glycosylase and gap-filling and ligation enzymes expressions in base excision repair pathway, which may have decreased DNA repair capacity. At the protein level, Cd induced the heat shock protein response, initiation of protein refolding as well as degradation by ubiquitin proteasome pathway, among other effects. Excess Cd also induced antioxidant responses, particularly glutathione metabolism, which play important roles in Cd chelation and anti-oxidation. This study provided the first molecular mechanisms of Cd toxicity on DNA and protein metabolism at protein levels, and identified molecular biomarkers for Cd toxicity in oysters.

Modifications of the soluble proteome of a mediterranean strain of the invasive neurotoxic dinoflagellate Alexandrium catenella under metal stress conditions

The soluble proteome of the mediterranean strain ACT03 of the invasive neurotoxic dinoflagellate Alexandrium catenella exposed to lead or zinc at 6, 12 or 18μM (total concentrations), or under control conditions, was characterized by two-dimensional gel electrophoresis (2-DE). Zinc reduced (P<0.05) the total number of protein spots (-41%, -52% and -60%, at 6, 12 or 18μM, respectively). Besides, most of the proteins constituting the soluble proteome were down-regulated in response to lead or zinc stresses. These proteins were involved mainly in photosynthesis (20-37% for lead; 36-50% for zinc) (ribulose-1,5-bisphosphate carboxylase/oxygenase: RUBISCO; ferredoxin-NADP⁺ reductase: FNR; peridinin-chlorophyll a-protein: PCP), and in the oxidative stress response (29-34% for lead; 17-36% for zinc) (superoxide dismutase: SOD; proteasome α/β subunits). These negative effects could be partly compensated by the up-regulation of specific proteins such as ATP-synthase β subunit (+16.3 fold after exposure to lead at 12μM). Indeed, an increase in the abundance of ATP-synthase could enrich the ATP pool and provide more energy available for the cells to survive under metal stress, and make the ATP-synthase transport of metal cations out of the cells more efficient. Finally, this study shows that exposure to lead or zinc have a harmful effect on the soluble proteome of A. catenella ACT03, but also suggests the existence of an adaptative proteomic response to metal stresses, which could contribute to maintaining the development of this dinoflagellate in trace metal-contaminated ecosystems.

Acclimatory processes are likely responsible for metal tolerance in oyster embryos

We aimed to determine if offspring of oysters from contaminated locations were more tolerant to metals, and whether this tolerance could be attributed to acclimation. Oysters from 10 estuaries were sampled, representing a gradient in metal contamination. Tolerance to metals of the F₁ offspring from adults residing in these estuaries was assessed. Then, adults from these estuaries were translocated to a single estuary and their offspring tolerance reassessed. No linear relationship was found between the Cu concentrations of adults and their offspring's tolerance to Cu. A positive linear relationship was found between the Zn concentration of adults and the Zn EC₅₀'s of their offspring. Zn tolerance was lost after translocation. Zn EC₅₀ values of offspring from transplanted adults bore no relation to the Zn EC₅₀'s of their location of origin. Thus the initial tolerance observed could be attributed to acclimation transferred to the F₁ generation.

Response of the pearl oyster Pinctada margaritifera to cadmium and chromium: Identification of molecular biomarkers

This study was designed to identify in the pearl oyster Pinctada margaritifera, used as a bio-accumulator, molecular biomarkers for the presence of heavy metals in the lagoon environment. Pearl oysters were exposed to 2 concentrations (1 and 10μgL^-1) of cadmium (Cd) and chromium (Cr) compared to a control. Twelve target genes encoding proteins potentially involved in the response to heavy metal contamination with antioxidant, detoxification or apoptosis activities were selected. P. margaritifera accumulated Cd but not Cr, and mortality was related to the amount of Cd accumulated in tissues. In response to Cd-Cr contamination, metallothionein (MT) was significantly up-regulated by Cd-Cr at both concentrations, while 7 others (SOD, CAT, GPX, GSTO, GSTM, CASP, MDR) were down-regulated. Based on the development of these molecular tools, we propose that the pearl oyster, P. margaritifera, could be used as a sentinel species for heavy metal contamination in the lagoons of tropical ecosystems.

Alterations of tissue metallothionein and vitellogenin concentrations in tropical cup oysters (Saccostrea sp.) following short-term (96h) exposure to cadmium

Metallothioneins and vitellogenins are low molecular weight proteins that have been used widely in environmental monitoring as biomarkers of exposure and damage to metals and estrogenic compounds, respectively. In the present study, the responses of metallothionein and vitellogenin tissue concentrations were measured following acute (96h) aqueous exposures to cadmium in Saccostrea sp., a tropical cup oyster native to the Western Pacific Ocean that has recently established itself in the Caribbean Sea. Adult oysters (1.5-5.0cm shell length) collected from the municipal marina of Santa Marta, Colombia (Caribbean Sea) and acclimated for 5days in the laboratory, were exposed to Cd at five concentrations (0, 1, 10, 100 and 1000μg/L) and their tissues (gills, digestive gland and adductor muscle) were analyzed in pools of 5 individuals (3 replicates per concentration). Metallothioneins in digestive glands of oysters exposed to Cd concentrations≥100μg/L showed a significant increase, from 8.0 to 14.8μg MT/mg total protein, whereas metallothionein concentrations in gills increased to lesser extent, and no differences were observed in adductor muscle. Metallothionein concentrations in digestive gland and gills correlated directly with whole soft tissue Cd concentrations (ranging from 2 to 297μg/g dw Cd). Vitellogenin in homogenates of oyster gonad tissue, after 96h of exposure to 1000μg/L Cd, were significantly lower (0.04mg P/g gonad) compared to control oysters (0.68mg P/g gonad), suggestive of an anti-estrogenic effect of Cd at high concentrations, whereas no significant changes in vitellogenin concentrations were observed at intermediate Cd exposure concentrations. This study confirms acute responses of metallothionein and vitellogenin concentrations in tissues of Saccostrea sp. exposed to high concentrations of cadmium (Cd≥100μg/L, 96h). The present results are first step towards validating the use of these two proteins as biomarkers of metal exposure in this species.

A comparative proteomic study on the effects of metal pollution in oysters Crassostrea hongkongensis

The metal pollution has posed great risk on the coastal organisms along the Jiulongjiang Estuary in South China. In this work, two-dimensional electrophoresis-based proteomics was applied to the oysters Crassostrea hongkongensis from metal pollution sites to characterize the proteomic responses to metal pollution. Metal accumulation and proteomic responses indicated that the oysters from BJ site were more severely contaminated than those from FG site. Compared with those oyster samples from the clean site (JZ), metal pollution induced cellular injuries, oxidative and immune stresses in oyster heapatopancreas from both BJ and FG sites via differential metabolic pathways. In addition, metal pollution in BJ site induced disturbance in energy and lipid metabolisms in oysters. Results indicated that cathepsin L and ferritin GF1 might be the biomarkers of As and Fe in oyster C. hongkongensis, respectively. This study demonstrates that proteomics is a useful tool for investigating biological effects induced by metal pollution.

Identification of a regulation network in response to cadmium toxicity using blood clam Tegillarca granosa as model

Clam, a filter-feeding lamellibranch mollusk, is capable to accumulate high levels of trace metals and has therefore become a model for investigation the mechanism of heavy metal toxification. In this study, the effects of cadmium were characterized in the gills of Tegillarca granosa during a 96-hour exposure course using integrated metabolomic and proteomic approaches. Neurotoxicity and disturbances in energy metabolism were implicated according to the metabolic responses after Cd exposure, and eventually affected the osmotic function of gill tissue. Proteomic analysis showed that oxidative stress, calcium-binding and sulfur-compound metabolism proteins were key factors responding to Cd challenge. A knowledge-based network regulation model was constructed with both metabolic and proteomic data. The model suggests that Cd stimulation mainly inhibits a core regulation network that is associated with histone function, ribosome processing and tight junctions, with the hub proteins actin, gamma 1 and Calmodulin 1. Moreover, myosin complex inhibition causes abnormal tight junctions and is linked to the irregular synthesis of amino acids. For the first time, this study provides insight into the proteomic and metabolomic changes caused by Cd in the blood clam T. granosa and suggests a potential toxicological pathway for Cd.

The biology of environmental stress: molecular biomarkers in Sydney rock oysters (Saccostrea glomerata)

This review describes our recent work on environmental stress in Sydney rock oysters, focusing on the identification of molecular biomarkers for ecotoxicological analysis. We begin by describing the environmental pressures facing coastal estuaries in Australia, with particular reference to Sydney Harbour. After providing that context, we summarise our transcriptional and proteomic analyses of Sydney rock oysters responding to chemical contamination and other forms of environmental stress. This work has shown that the intracellular processes of oysters are highly responsive to environmental threats. Our data agree with the broader literature, which suggests that there is a highly conserved intracellular stress response in oysters involving a limited number of biological processes. We conclude that many effective molecular markers for environmental biomonitoring are likely to lie within these biological pathways.

Differential proteomic response of Sydney rock oysters (Saccostrea glomerata) to prolonged environmental stress

Exposure to prolonged environmental stress can have impacts on the cellular homeostasis of aquatic organisms. The current study employed two-dimensional electrophoresis (2-DE) to test whether exposure to impaired water quality conditions in the Sydney Harbour estuary has significantly altered the proteomes of the resident Sydney rock oyster (Saccostrea glomerata). Adult S. glomerata were sampled from four bays in the estuary. Each bay consisted of a "high-impact" site adjacent to point sources of chemical contamination (e.g., storm drains/canals or legacy hotspots) and a "low-impact" site located ∼5km away from point sources. A mixture of environmental stressors differed significantly between high- and low-impact sites. Specifically, PAHs, PCBs, tributyltin, Pb, and Zn were significantly elevated in oyster tissues from high-impact sites, together with depleted dissolved oxygen and low pH in the water column. A 2-DE proteomics analysis subsequently identified 238 protein spots across 24 2-DE gels, of which 27-50 spots differed significantly in relative intensity between high- and low-impact sites per bay. Twenty-five percent of the differential spots were identified in more than one bay. The identities of 80 protein spots were determined by mass spectrometry. HSP 70, PPIB, and radixin were the three most highly expressed differential proteins. Despite the largely unique proteomes evident in each bay, functional annotations revealed that half of the differentially expressed proteins fell into just two subcellular functional categories-energy metabolism and the cytoskeleton. These findings provide a framework to further investigate adaptation of cellular mechanisms to prolonged stress in S. glomerata.

Metal-contaminated resuspended sediment particles are a minor metal-uptake route for the Sydney rock oyster (Saccostrea glomerata)--A mesocosm study, Sydney Harbour estuary, Australia

Resuspension of surficial sediments is considered a key process influencing bioaccumulation of metals in filter-feeders in the contaminated Sydney Harbour estuary (Australia). However, previous investigations were unable to establish a significant relationship between metals in sediments or suspended particulate matter (SPM) and oyster tissue concentrations. This study used a 60-d laboratory mesocosm experiment to expose Sydney rock oysters, Saccostrea glomerata, to a natural range of SPM concentrations with different SPM-metal concentrations. Dissolved metal concentrations were low and the availability of algae provided as food was constant for all treatments. Tissue metal concentrations of Cu, Pb and Zn increased significantly, however, no relationship was determined between tissue metal concentrations in the oyster and either SPM or SPM-metal concentrations. The results indicated that exposure to resuspended contaminated sediment particles contributed little to the observed metal uptake. Dissolved or algae food sources appear to be more important for metal accumulation in these oysters.

Proteomic analysis of hemolymph from poly(I:C)-stimulated Crassostrea gigas

Synthetic double stranded RNA (Poly(I:C)) injection of Crassostrea gigas results in a systemic antiviral response involving many evolutionary conserved antiviral effectors (ISGs). Compared to mammals, the timing of C. gigas ISG expression to viral or poly(I:C) injection is delayed (>12 h p.i.). It could be interpreted that a cytokine is responsible for the systemic, but delayed expression of C. gigas ISGs. We therefore analysed the acellular fraction of C. gigas hemolymph by two-dimensional electrophoresis (2-DE) to identify hemolymph proteins induced by poly(I:C). Poly(I:C) injection increased the relative intensity of four protein spots. These protein spots were identified by tandem mass spectrometry (LC-MS/MS) as a small heat shock protein (sHSP), poly(I:C)-inducible protein 1 (PIP1) and two isoforms of C1q-domain containing protein (C1qDC). RT-qPCR analysis confirmed that the genes encoding these proteins are induced in hemocytes of C. gigas injected with poly(I:C) (p < 0.05). Proteomic data from this experiment corroborates previous microarray and whole transcriptome studies that have reported up-regulation of C1qDC and sHSP during mass mortality events among farmed oysters.

Combined metabolome and proteome analysis of the mantle tissue from Pacific oyster Crassostrea gigas exposed to elevated pCO2

Ocean acidification (OA) has been found to affect an array of normal physiological processes in mollusks, especially posing a significant threat to the fabrication process of mollusk shell. In the current study, the impact of exposure to elevated pCO2 condition was investigated in mantle tissue of Crassostrea gigas by an integrated metabolomic and proteomic approach. Analysis of metabolome and proteome revealed that elevated pCO2 could affect energy metabolism in oyster C. gigas, marked by differentially altered ATP, succinate, MDH, PEPCK and ALDH levels. Moreover, the up-regulated calponin-2, tropomyosins and myosin light chains indicated that elevated pCO2 probably caused disturbances in cytoskeleton structure in mantle tissue of oyster C. gigas. This work demonstrated that a combination of proteomics and metabolomics could provide important insights into the effects of OA at molecular levels.

Next-generation proteomics: toward customized biomarkers for environmental biomonitoring

Because of their ecological representativeness, invertebrates are commonly employed as test organisms in ecotoxicological assessment; however, to date, biomarkers employed for these species were the result of a direct transposition from vertebrates, despite deep evolutionary divergence. To gain efficiency in the diagnostics of ecosystem health, specific biomarkers must be developed. In this sense, next-generation proteomics enables the specific identification of proteins involved in key physiological functions or defense mechanisms, which are responsive to ecotoxicological challenges. However, the analytical investment required restricts use in biomarker discovery. Routine biomarker validation and assays rely on more conventional mass spectrometers. Here, we describe how proteomics remains a challenge for ecotoxicological test organisms because of the lack of appropriate protein sequences databases, thus restricting the analysis on conserved and ubiquitous proteins. These limits and some strategies used to overcome them are discussed. These new tools, such as proteogenomics and targeted proteomics, should result in new biomarkers specific to relevant environmental organisms and applicable to routine ecotoxicological assessment.

Metal accumulation and differentially expressed proteins in gill of oyster (Crassostrea hongkongensis) exposed to long-term heavy metal-contaminated estuary

Bio-accumulation and bio-transmission of toxic metals and the toxicological responses of organisms exposed to toxic metals have been focused, due to heavy metal contaminations have critically threatened the ecosystem and food security. However, still few investigations focused on the responses of certain organisms exposed to the long term and severe heavy metal contamination in specific environments. In present investigation, the Hong Kong oyster, Crassostrea hongkongensis were obtained from 3 sites which were contaminated by different concentrations of heavy metals (such as zinc, copper, manganese and lead etc.), respectively. Heavy metal concentrations in the sea water samples collected from the 3 sites and the dissected tissues of the oysters with blue visceral mass were determinated to estimate the metal contamination levels in environments and the bio-accumulation ratios of the heavy metals in the different tissues of oysters. Moreover, Proteomic methods were employed to analyze the differentially expressed proteins in the gills of oysters exposed to long-term heavy metal contaminations. Results indicated that the Jiulong River estuary has been severely contaminated by Cu, Zn and slightly with Cr, Ni, Mn, etc, moreover, Zn and Cu were the major metals accumulated by oysters to phenomenally high concentrations (more than 3.0% of Zn and about 2.0% of Cu against what the dry weight of tissues were accumulated), and Cr, Ni, Mn, etc were also significantly accumulated. The differentially expressed proteins in the gills of oysters exposed to heavy metals participate in several cell processes, such as metal binding, transporting and saving, oxidative-reduction balance maintaining, stress response, signal transduction, etc. Significantly up-regulated expression (about 10 folds) of an important metal binding protein, metallothionein (MT) and granular cells was observed in the gills of oysters exposed to long-term and severely heavy-metal-contaminated estuary, it suggested that binding toxic metals with metallothionein-like proteins (MTLP) and storing toxic metals in metal-rich granules (MRG) with insoluble forms were the important strategies of oyster to detoxify the toxic metals and adapt to the high level of metal-contaminated environment. Most of the stress and immunity responsive proteins, such as heat shock proteins (HSP), extracellular superoxide dismutase (ECSOD) and cavortin, and the cellular redox reaction relative proteins such as 20G-Fe (II) oxygenase family oxidoreductase, aldehyde dehydrogenase and retinal dehydrogenase 2, were detected significantly down-regulated in the gills of oysters exposed to long term heavy metal contaminated environments, it indicated that long term exposure different from emergent exposure to heavy metal contamination may significantly suppress the stress and immunity response system of oysters. Moreover, Formin homology 2 domain containing protein (FH2). The only protein domain to directly nucleate actin monomers into unbranched filament polymers, by which will subsequently control gene expression and chromatin remodelling complexes, was also detected greatly up-regulated in the gills of oysters exposed to long-term heavy metal contaminations. It indicated that nuclear activity regulation may also be important for oyster to adapt to the long-term heavy-metal-contaminated environment.

Proteomic analysis in caged Mediterranean crab (Carcinus maenas) and chemical contaminant exposure in Téboulba Harbour, Tunisia

This study uses proteomics approach to assess the toxic effects of contaminants in the Mediterranean crab (Carcinus maenas) after transplantation into Téboulba fishing harbour. High levels of aliphatic and aromatic hydrocarbons were detected in sediments. Although their effects on vertebrates are well described, little is known about their early biological effects in marine invertebrates under realistic conditions. Protein expression profiles of crabs caged for 15, 30 and 60 days were compared to unexposed animals. Nineteen proteins with significant expression differences were identified by capLC-µESI-IT MS/MS and homology search on databases. Differentially expressed proteins were assigned to five different categories of biological function including: (1) chitin catabolism, (2) proteolysis, (3) exoskeleton biosynthesis, (4) protein folding and stress response, and (5) transport. The proteins showing major expression changes in C. maenas after different caging times may be considered as novel molecular biomarkers for effectively biomonitoring aquatic environment contamination.

Impact of benzo(a)pyrene, Cu and their mixture on the proteomic response of Mytilus galloprovincialis

In natural waters, chemical interactions between mixtures of contaminants can result in potential synergistic and/or antagonic effects in aquatic animals. Benzo(a)pyrene (BaP) and copper (Cu) are two widespread environmental contaminants with known toxicity towards mussels Mytilus spp. The effects of the individual and the interaction of BaP and Cu exposures were assessed in mussels Mytilus galloprovincialis using proteomic analysis. Mussels were exposed to BaP [10 μg L(-1) (0.396 μM)], and Cu [10 μg L(-1) (0.16 μM)], as well as to their binary mixture (mixture) for a period of 7 days. Proteomic analysis showed different protein expression profiles associated to each selected contaminant condition. A non-additive combined effect was observed in mixture in terms of new and suppressed proteins. Proteins more drastically altered (new, suppressed and 2-fold differentially expressed) were excised and analyzed by mass spectrometry, and eighteen putatively identified. Protein identification demonstrated the different accumulation, metabolism and chemical interactions of BaP, Cu and their mixture, resulting in different modes of action. Proteins associated with adhesion and motility (catchin, twitchin and twitchin-like protein), cytoskeleton and cell structure (α-tubulin and actin), stress response (heat shock cognate 71, heat shock protein 70, putative C1q domain containing protein), transcription regulation (zinc-finger BED domain-containing and nuclear receptor subfamily 1G) and energy metabolism (ATP synthase F0 subunit 6 protein and mannose-6-phosphate isomerase) were assigned to all three conditions. Cu exposure alone altered proteins associated with oxidative stress (glutathione-S-transferase) and digestion, growth and remodelling processes (chitin synthase), while the mixture affected only one protein (major vault protein) possibly related to multi drug resistance. Overall, new candidate biomarkers, namely zinc-finger BED domain-containing protein, chitin synthase and major vault protein, were also identified for BaP, Cu and mixture, respectively.

Proteomic analysis of the dorsal and ventral hippocampus of rats maintained on a high fat and refined sugar diet

The typical Western diet, rich in high saturated fat and refined sugar (HFS), has been shown to increase cognitive decline with aging and Alzheimer's disease, and to affect cognitive functions that are dependent on the hippocampus, including memory processes and reversal learning. To investigate neurophysiological changes underlying these impairments, we employed a proteomic approach to identify differentially expressed proteins in the rat dorsal and ventral hippocampus following maintenance on an HFS diet. Rats maintained on the HFS diet for 8 weeks were impaired on a novel object recognition task that assesses memory and on a Morris Water Maze task assessing reversal learning. Quantitative label-free shotgun proteomic analysis was conducted on biological triplicates for each group. For the dorsal hippocampus, 59 proteins were upregulated and 36 downregulated in the HFS group compared to controls. Pathway ana-lysis revealed changes to proteins involved in molecular transport and cellular and molecular signaling, and changes to signaling pathways including calcium signaling, citrate cycle, and oxidative phosphorylation. For the ventral hippocampus, 25 proteins were upregulated and 27 downregulated in HFS fed rats. Differentially expressed proteins were involved in cell-to-cell signaling and interaction, and cellular and molecular function. Changes to signaling pathways included protein ubiquitination, ubiquinone biosynthesis, oxidative phosphorylation, and mitochondrial dysfunction. This is the first shotgun proteomics study to examine protein changes in the hippocampus following long-term consumption of a HFS diet, identifying changes to a large number of proteins including those involved in synaptic plasticity and energy metabolism. All MS data have been deposited in the ProteomeXchange with identifier PXD000028.

Differential effects of metal contamination on the transcript expression of immune- and stress-response genes in the Sydney Rock oyster, Saccostrea glomerata

Environmental contamination by metals is a serious threat to the biological sustainability of coastal ecosystems. Our current understanding of the potential biological effects of metals in these ecosystems is limited. This study tested the transcriptional expression of immune- and stress-response genes in Sydney Rock oysters (Saccostrea glomerata). Oysters were exposed to four metals (cadmium, copper, lead and zinc) commonly associated with anthropogenic pollution in coastal waterways. Seven target genes (superoxide dismutase, ferritin, ficolin, defensin, HSP70, HSP90 and metallothionein) were selected. Quantitative (real-time) PCR analyses of the transcript expression of these genes showed that each of the different metals elicited unique transcriptional profiles. Significant changes in transcription were found for 18 of the 28 combinations tested (4 metals × 7 genes). Of these, 16 reflected down-regulation of gene transcription. HSP90 was the only gene significantly up-regulated by metal contamination (cadmium and zinc only), while defensin expression was significantly down-regulated by exposure to all four metals. This inhibition could have a significant negative effect on the oyster immune system, promoting susceptibility to opportunistic infections and disease.

Shotgun proteomics as a viable approach for biological discovery in the Pacific oyster

Shotgun proteomics offers an efficient means to characterize proteins in a complex mixture, particularly when sufficient genomic resources are available. In order to assess the practical application of shotgun proteomics in the Pacific oyster (Crassostrea gigas), liquid chromatography coupled with tandem mass spectrometry was used to characterize the gill proteome. Using information from the recently published Pacific oyster genome, 1043 proteins were identified. Biological samples (n = 4) and corresponding technical replicates (three) were similar in both specific proteins identified and expression, as determined by normalized spectral abundance factor. A majority of the proteins identified (703) were present in all biological samples. Functional analysis of the protein repertoire illustrates that these proteins represent a wide range of biological processes, supporting the dynamic function of the gill. These insights are important for understanding environmental influences on the oyster, because the gill tissue acts as the interface between the oyster and its environment. In silico analysis indicated that this sequencing effort identified a large proportion of the complete gill proteome. Together, these data demonstrate that shotgun sequencing is a viable approach for biological discovery and will play an important role in future studies of oyster physiology.

Proteomic analysis of Sydney Rock oysters (Saccostrea glomerata) exposed to metal contamination in the field

This study used proteomics to assess the impacts of metal contamination in the field on Sydney Rock oysters. Oysters were transplanted into Lake Macquarie, NSW, for two weeks in both 2009 and 2010. Two-dimensional electrophoresis identified changes in protein expression profiles of oyster haemolymph between control and metal contaminated sites. There were unique protein expression profiles for each field trial. Principal components analysis attributed these differences in oyster proteomes to the different combinations and concentrations of metals and other environmental variables present during the three field trials. Identification of differentially expressed proteins showed that proteins associated with cytoskeletal activity and stress responses were the most commonly affected biological functions in the Sydney Rock oyster. Overall, the data show that proteomics combined with multivariate analysis has the potential to link the effects of contaminants with biological consequences.

Marine proteomics: a critical assessment of an emerging technology

The application of proteomics to marine sciences has increased in recent years because the proteome represents the interface between genotypic and phenotypic variability and, thus, corresponds to the broadest possible biomarker for eco-physiological responses and adaptations. Likewise, proteomics can provide important functional information regarding biosynthetic pathways, as well as insights into mechanism of action, of novel marine natural products. The goal of this review is to (1) explore the application of proteomics methodologies to marine systems, (2) assess the technical approaches that have been used, and (3) evaluate the pros and cons of this proteomic research, with the intent of providing a critical analysis of its future roles in marine sciences. To date, proteomics techniques have been utilized to investigate marine microbe, plant, invertebrate, and vertebrate physiology, developmental biology, seafood safety, susceptibility to disease, and responses to environmental change. However, marine proteomics studies often suffer from poor experimental design, sample processing/optimization difficulties, and data analysis/interpretation issues. Moreover, a major limitation is the lack of available annotated genomes and proteomes for most marine organisms, including several "model species". Even with these challenges in mind, there is no doubt that marine proteomics is a rapidly expanding and powerful integrative molecular research tool from which our knowledge of the marine environment, and the natural products from this resource, will be significantly expanded.

Protein expression from zooplankton communities in a metal contaminated NW mediterranean coastal ecosystem

Bidimensional and monodimensional polyacrylamide gel electrophoresis were used to study protein expression from zooplankton collected in thirteen stations of Toulon Bay (NW Mediterranean). In this ecosystem, Little Bay showed higher trace metal concentrations (13.5-23.8 nM for Cu, 0.73-1.24 nM for Pb, 27.8-58.7 nM for Zn) than Large Bay (Cu 2.2-15.6 nM; Pb 0.19-0.78 nM; Zn 9.0-38.8 nM). Trace metals positively correlated (p < 0.05) with expression of four zooplankton proteins (MW in kDa/pI: 25.0/5.6; 48.8/4.1; 38.2/4.4; 38.3/5.8) and with biomass of Oithona nana, predominant copepod in Little Bay. Sequencing by LC-MS/MS putatively provided zooplankton identity of these proteins: they were cytoskeleton actin, except one protein that was the chaperone calreticulin. We suggest that actin and calreticulin could be regarded as zooplankton markers of metal stress and be involved in a possible tolerance of O. nana to contamination, contributing to its development in a marine perturbed ecosystem.

Effects of triclosan in the freshwater mussel Dreissena polymorpha: a proteomic investigation

Triclosan (TCS, 5-chloro-2-(2,4-dichlorophenoxy)phenol) is commonly used in several personal care products, textiles, and children's toys. Because the removal of TCS by wastewater treatment plants is incomplete, its environmental fate is to be discharged into freshwater ecosystems, where its ecotoxicological impact is still largely unexplored. Previously, we began a structured multi-tiered approach in order to evaluate TCS toxicity in the freshwater mussel Dreissena polymorpha. The results of our previous studies, based on in vitro and in vivo experiments, highlighted a pronounced cytogenotoxic effect exerted by TCS, and showed that an increase in oxidative stress was likely to be one of its main toxic mechanisms. In this work, in order to investigate TCS toxicity mechanisms in aquatic non-target species in greater depth, we decided to use a proteomic approach, analysing changes in protein expression profiles in gills of D. polymorpha exposed for seven days to TCS. Moreover, thiobarbituric acid reactive substances (TBARS) were measured to investigate further the role played by TCS in inducing oxidative stress. Finally, TCS bioaccumulation in mussel tissues was also assessed, to ensure an effective accumulation of the toxicant. Our results not only confirmed the role played by TCS in inducing oxidative stress, but furthered knowledge about the mechanism exerted by TCS in inducing toxicity in an aquatic non-target organisms. TCS induced significant alterations in protein expression profiles in gills of D. polymorpha. The wide range of proteins affected suggested that this chemical has marked effects on various biological processes, especially those involved in calcium binding or stress response. We also confirmed that the proteomic analysis, using 2-DE and de novo sequencing, is a reliable and powerful approach to investigate cellular responses to pollutants in a non-model organism with few genomic sequences available in databases.

Cadmium-induced changes in trace element bioaccumulation and proteomics perspective in four marine bivalves

Bivalves are employed widely as biomonitors of metal pollution and proteomics has increasingly been applied to solve ecotoxicological issues. This study aimed to investigate the effects of Cd exposure on the bioaccumulation of other trace elements and reveal the molecular mechanisms using proteomics technologies. The results showed that Cd exposure resulted in remarkable changes in body concentrations of Zn, Cu, Ag, Co, Ni, Pb, and Se in four marine bivalves (scallop Chlamys nobilis, clam Ruditapes philippinarum, mussel Perna viridis, and oyster Saccostrea cucullata). Generally, the bivalves exposed to higher Cd concentration accumulated higher concentrations of Zn, Cu, and Se, but a lower concentration of Co. The accumulation of Ag, Ni, and Pb was specific for different species. The data strongly suggest that the influences of one metal exposure on the bioaccumulation of other metals/metalloids need to be considered in interpreting body concentrations of the elements in the biomonitors. Cd exposure had little effect on bivalve proteomes, and the identified proteins were insufficient to explain the observed disruption of trace element metabolism. However, protein expression signatures composed of the altered proteins could distinguish the clams and the mussels with different body Cd levels. The strong up-regulation of galectin in Cd-exposed oysters indicated the protein as a novel biomarker in environmental monitoring.

Proteomic research in bivalves: towards the identification of molecular markers of aquatic pollution

Biomonitoring of aquatic environment and assessment of ecosystem health play essential roles in the development of effective strategies for the protection of the environment, human health and sustainable development. Biomarkers of pollution exposure have been extensively utilized in the last few decades to monitor the health of organisms and hence assess environmental status. However, the use of single biomarkers against biotic or abiotic stressors may be limited by the lack of sensitivity and specificity. Therefore, more recently, the search for novel biomarkers has been focused on the application of OMICS methodologies. Environmental proteomics focuses on the analysis of an organism's proteome and the detection of changes in the level of individual proteins/peptides in response to environmental stressors. Proteomics can provide a more robust approach for the assessment of environmental stress and therefore exposure to pollutants. This review aims to summarize the proteomic research in bivalves, a group of sessile and filter feeding organisms that play an important function as "sentinels" of the aquatic environment. A description of the main proteomic methodologies is provided. The current knowledge in bivalves' toxicology, achieved with proteomics, is reported describing the main biochemical markers identified. A brief discussion regarding future challenges in this area of research emphasizing the development of more descriptive gene/protein databases that could support the OMICs approaches is presented.

Proteomic discovery of biomarkers of metal contamination in Sydney Rock oysters (Saccostrea glomerata)

In the current study we examined the effects of metal contamination on the protein complement of Sydney Rock oysters. Saccostrea glomerata were exposed for 4 days to three environmentally relevant concentrations (100 μg/l, 50 μg/l and 5 μg/l) of cadmium, copper, lead and zinc. Protein abundances in oyster haemolymph from metal-exposed oysters were compared to those from non-exposed controls using two-dimensional electrophoresis to display differentially expressed proteins. Differentially expressed proteins were subsequently identified using tandem mass spectrometry (LC-MS/MS), to assign their putative biological functions. Unique sets of differentially expressed proteins were affected by each metal, in addition to proteins that were affected by more than one metal. The proteins identified included some that are commonly associated with environmental monitoring, such as HSP 70, and other novel proteins not previously considered as candidates for molecular biomonitoring. The most common biological functions of proteins were associated with stress response, cytoskeletal activity and protein synthesis.