The transcriptomic and biochemical responses of blood clams (Tegillarca granosa) to prolonged intermittent hypoxia

The blood clam (Tegillarca granosa), a marine bivalve of ecological and economic significance, often encounters intermittent hypoxia in mudflats and aquatic environments. To study the response of blood clam foot to prolonged intermittent hypoxia, the clams were exposed to intermittent hypoxia conditions (0.5 mg/L dissolved oxygen, with a 12-h interval) for 31 days. Initially, transcriptomic analysis was performed, uncovering a total of 698 differentially expressed genes (DEGs), with 236 upregulated and 462 downregulated. These genes show enrichments in signaling pathways related to glucose metabolism, sugar synthesis and responses to oxidative stress. Furthermore, the activity of the enzyme glutathione peroxidase (GPx) and the levels of gpx1 mRNA showed gradual increases, reaching their peak on the 13th day of intermittent hypoxia exposure. This observation suggests an indirect protective role of GPx against oxidative stress. The results of this study make a significantly contribute to our broader comprehensive of the physiological, biochemical responses, and molecular reactions governing the organization of foot muscle tissue in marine bivalves exposed to prolonged intermittent hypoxic conditions.

Genome-wide identification and characteristic analysis of ETS gene family in blood clam Tegillarca granosa

BACKGROUND

ETS transcription factors, known as the E26 transformation-specific factors, assume a critical role in the regulation of various vital biological processes in animals, including cell differentiation, the cell cycle, and cell apoptosis. However, their characterization in mollusks is currently lacking.

RESULTS

The current study focused on a comprehensive analysis of the ETS genes in blood clam Tegillarca granosa and other mollusk genomes. Our phylogenetic analysis revealed the absence of the SPI and ETV subfamilies in mollusks compared to humans. Additionally, several ETS genes in mollusks were found to lack the PNT domain, potentially resulting in a diminished ability of ETS proteins to bind target genes. Interestingly, the bivalve ETS1 genes exhibited significantly high expression levels during the multicellular proliferation stage and in gill tissues. Furthermore, qRT-PCR results showed that Tg-ETS-14 (ETS1) is upregulated in the high total hemocyte counts (THC) population of T. granosa, suggesting it plays a significant role in stimulating hemocyte proliferation.

CONCLUSION

Our study significantly contributes to the comprehension of the evolutionary aspects concerning the ETS gene family, while also providing valuable insights into its role in fostering hemocyte proliferation across mollusks.

A C-type lectin with a single carbohydrate-recognition domain (CRD) containing unique QPN/WDD motifs from Tegillarca granosa is involved in the innate immune defense

C-type lectins (CTLs), a superfamily of Ca2+-dependent carbohydrate-recognition proteins, serve as pattern recognition receptors (PRRs) in the immune response of many species. However, little is currently known about the CTLs of the commercially and ecologically important bivalve species, blood clam (Tegillarca granosa). In this study, a CTL (designated as TgCTL-1) with a single carbohydrate-recognition domain (CRD) containing unique QPN/WDD motifs was identified in the blood clam through transcriptome and whole-genome searching. Multiple alignment and phylogenetic analysis strongly suggested that TgCTL-1 was a new member of the CTL superfamily. Expression analysis demonstrated that TgCTL-1 was highly expressed in the hemocytes and visceral mass of the clam under normal condition. In addition, the expression of TgCTL-1 was shown to be significantly up-regulated upon pathogen challenge. Moreover, the recombinant TgCTL-1 (rTgCTL-1) displayed agglutinating and binding activities against both the gram-positive and gram-negative bacteria tested in a Ca2+-dependent manner. Furthermore, it was found that the in vitro phagocytic activity of hemocytes was significantly enhanced by rTgCTL-1. In general, our results showed that TgCTL-1 was an inducible acute-phase secretory protein, playing crucial roles in recognizing, agglutinating, and binding to pathogenic bacteria as well as modulating phagocytic activity of hemocytes in the innate immune defense of blood clam.

Genome-wide identification and immune response analysis of serine protease inhibitor genes in the blood clam Tegillarca granosa

Serine protease inhibitors (SPIs) are the main regulators of serine protease activities. In this study, we present a genome-wide identification of SPI genes in T. granosa（TgSPI genes）and their expression characteristics in respond to Vibrio stress. A total of 102 TgSPI genes belonging to eight families, including Serpin, TIL (trypsin inhibitor like cysteine rich domain), Kunitz, Kazal, I84, Pacifastin, WAP (whey acidic protein) and A2M (Alpha-2-macroglobulin) were identified, while no genes belonging to Bowman-Birk, amfpi and Antistasin families were identified. The Kazal family has the most TgSPI genes with 38, and 11 TgSPI genes belong to the mollusc-specific I84 family. The TgSPI genes were found to be randomly distributed on 17 chromosomes with 12 tandem duplicate gene pairs. Expression profiles showed that most TgSPI genes were mainly expressed in immune-related tissues such as hepatopancreas, gill and mantle. In the hepatopancreas, most of TgSPI genes were sensitive to Vibrio stress, 28 and 29 TgSPI genes were up-regulated and down-regulated, respectively. Some up-regulated genes with signal peptides, such as the TgSPIs of I84 family, may act as a mechanism to directly prevent Vibrio from invasion. Six Kazal-type TgSPIs (TgSPI29, 45, 49, 50, 51 and 52) were intracellular proteins and their expression was down-regulated in hemocytes after Vibrio stress. This may have boosted protease activity in hemocytes to the point that more hemoglobin derived peptides were produced and secreted into the hemolymph to exert their anti-Vibrio effects. These findings may provide valuable information for further clarifying the roles of SPIs in the immune defense and will benefit future exploration of the immune function of SPIs in molluscs.

Molecular cloning, characterization, and tissue distribution of c-Myc from blood clam Tegillarca granosa and its role in cadmium-induced stress response

Cadmium (Cd) pollution threatens the cultivation of the blood clam Tegillarca granosa (T. granosa) in coastal regions of the East China Sea. The molecular mechanisms regulating Cd stress response and detoxification in blood clams are largely unclear. In the present study, the full-length T. granosa c-Myc (Tgc-Myc) cDNA was cloned for the first time. The 3063-bp cDNA consisted of a 129-bp 5' untranslated region (UTR), a 1746-bp 3' UTR, and a 1188-bp open reading frame encoding a predicted protein of 395 amino acid residues. The predicted protein had a calculated molecular weight of 44.9 kDa and an estimated isoelectric point of 6.82. The predicted protein contained an N-terminal transactivation domain and a C-terminal basic helix-loop-helix leucine zipper domain, which are conserved functional domains of c-Myc proteins. Tgc-Myc showed broad tissue distribution in blood clams, with the highest expression detected in the gill and hepatopancreas. Exposure to Cd, a major heavy metal pollutant in coastal regions of the East China Sea, induced Tgc-Myc expression in gill tissues. Tgc-Myc knockdown led to reduced expression of a variety of stress response/detoxification genes in blood clams cultivated in Cd-contaminated seawater. Tgc-Myc knockdown also led to decreased expression of IGF1R, a proto-oncogene that promotes cell proliferation. These findings indicated that Tgc-Myc regulates Cd-induced stress response and detoxification in blood clams. The upregulation of Tgc-Myc may serve as an approach to generate strains with an enhanced detoxification response and consequently a low heavy metal buildup.

Genomic Insights into the Origin and Evolution of Molluscan Red-Bloodedness in the Blood Clam Tegillarca granosa

Blood clams differ from their molluscan kins by exhibiting a unique red-blood (RB) phenotype; however, the genetic basis and biochemical machinery subserving this evolutionary innovation remain unclear. As a fundamental step toward resolving this mystery, we presented the first chromosome-level genome and comprehensive transcriptomes of the blood clam Tegillarca granosa for an integrated genomic, evolutionary, and functional analyses of clam RB phenotype. We identified blood clam-specific and expanded gene families, as well as gene pathways that are of RB relevant. Clam-specific RB-related hemoglobins (Hbs) showed close phylogenetic relationships with myoglobins (Mbs) of blood clam and other molluscs without the RB phenotype, indicating that clam-specific Hbs were likely evolutionarily derived from the Mb lineage. Strikingly, similar to vertebrate Hbs, blood clam Hbs were present in a form of gene cluster. Despite the convergent evolution of Hb clusters in blood clam and vertebrates, their Hb clusters may have originated from a single ancestral Mb-like gene as evidenced by gene phylogeny and synteny analysis. A full suite of enzyme-encoding genes for heme synthesis was identified in blood clam, with prominent expression in hemolymph and resembling those in vertebrates, suggesting a convergence of both RB-related Hb and heme functions in vertebrates and blood clam. RNA interference experiments confirmed the functional roles of Hbs and key enzyme of heme synthesis in the maintenance of clam RB phenotype. The high-quality genome assembly and comprehensive transcriptomes presented herein serve new genomic resources for the super-diverse phylum Mollusca, and provide deep insights into the origin and evolution of invertebrate RB.

Modulatory function of calmodulin on phagocytosis and potential regulation mechanisms in the blood clam Tegillarca granosa

Unlike vertebrate species, invertebrates lack antigen-antibody mediated immune response and mainly rely on haemocyte phagocytosis to fight against pathogen infection. Recently, studies conducted in model vertebrates demonstrated that the multifunctional protein calmodulin (CaM) plays an important role in regulating immune responses. However, the intrinsic relation between CaM and phagocytosis process remains poorly understood in invertebrate species such as bivalve mollusks. Therefore, in the present study, the immunomodulatory function of CaM on haemocyte phagocytosis was verified in the blood clam, Tegillarca granosa, using the CaM-specific inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7). Results obtained show that CaM inhibition significantly suppressed the phagocytic activity of haemocytes. In addition, CaM inhibition constrained intracellular Ca²⁺ elevation, hampered actin cytoskeleton assembly, suppressed calcineurin (CaN) activity, and disrupted NF-κB activation in haemocytes upon LPS induction. Furthermore, expression of seven selected genes from the actin cytoskeleton regulation- and immune-related pathways were significantly downregulated whereas those of CaM and CaN from the Ca²⁺-signaling pathway were significantly upregulated by in vitro incubation of haemocytes with W-7. For the first time, the present study demonstrated that CaM play an important role in phagocytosis modulation in bivalve species. In addition, the intracellular Ca²⁺ and downstream Ca²⁺-signaling-, actin cytoskeleton regulation-, and immune-related pathways offer candidate routes through which CaM modulates phagocytosis.

Microplastics in beach sediments and cockles (Anadara antiquata) along the Tanzanian coastline

Little is known about the prevalence of microplastics (MPs) in East Africa. In the present study, sediments were sampled at 18 sites along the Tanzanian coast that exhibit different levels of anthropogenic activity and were extracted using floatation methodology. Cockles (Anadara antiquata) were collected only from eight sites and MPs were extracted following NaOH digestion. MPs were most abundant at Mtoni Kijichi Creek (MKC, 2972 ± 238 particles kg^-1 dry sediment), an industrial port in Dar es Salaam, and significantly higher than all other sites where the abundance range was 15-214 particles kg^-1 dry sediment (p < 0.05, one-way ANOVA). Fragments and fibers were found at all sites. Polypropylene and polyethylene were identified polymers. MPs were found in cockles from all sampled sites with both frequencies of occurrence and MPs per individual subject to site-specific variation. This study provides a baseline of MP data in a previously uninvestigated area.

Acetylcholine suppresses phagocytosis via binding to muscarinic- and nicotinic-acetylcholine receptors and subsequently interfering Ca2+- and NFκB-signaling pathways in blood clam

Though immunomodulation via cholinergic neurotransmitter acetylcholine (ACh), an important part of neuroendocrine-immune (NEI) regulatory network, has been well established in vertebrate species, the mechanisms remain poorly understood in invertebrates. In the present study, the immunomodulatory effect of ACh on haemocyte phagocytosis was investigated in an invertebrate bivalve species, Tegillarca granosa. Data obtained showed that in vitro ACh incubation suppressed phagocytic activity of haemocytes along with a significant elevation in intracellular Ca²⁺. In addition, the expressions of genes from Ca²⁺ signaling pathway were significantly induced whereas those from NF-κB signaling pathway were significantly down-regulated by ACh incubation. Furthermore, these adverse impacts of ACh were significantly relieved by the blocking of muscarinic acetylcholine receptors (mAChRs) or nicotinic acetylcholine receptors (nAChRs) using corresponding antagonists. Our study suggests that ACh suppresses phagocytosis via binding to both mAChRs and nAChRs, which disrupts intracellular Ca²⁺ homeostasis and subsequently interferes with downstream Ca²⁺ and NF-κB signaling pathways.

Morphologic, cytometric and functional characterisation of Anadara kagoshimensis hemocytes

Circulating hemocytes of ark clam, Anadara kagoshimensis, were investigated using light microscopy and flow cytometry. Hemolymph contained 3 morphotype of cells, amebocytes, erythrocytes and intermediate type cells, which formed two distinct subpopulations on flow cytometric dot plots. Large cells (intermediate morphotype and erythrocytes) amounted 85.6 ± 2.8% total cells in hemolymph. Erythrocytes were hemoglobin-containing cells with up to 40 granules presented in the cytoplasm. All hemocyte types, observed in the ark clam hemolymph demonstrated equal capacity to spontaneous production of reactive oxygen species.

Single and joint oxidative stress of cadmium and phenanthrene on the Bivalve Anadara subcrenata

Single and joint oxidative stress of cadmium (Cd) and phenanthrene (Phe) on Anadara subcrenata were investigated under laboratory conditions with biomarkers such as reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD) and total antioxidant capacity (TAOC). The results indicated that the ROS level in Anadara subcrenata exposed to Cd and Phe significantly (P < 0.05) increased during the early exposure stage, and the TAOC level and SOD activity were induced as the response of the antioxidant defense system, and this followed a damage, recovery or acclimation event. The MDA content was negatively correlated with SOD activity. As the time went on, the ROS level decreased gradually and was close to that in the control after 9 days; the TAOC level decreased accordingly, but the recovery rate of the SOD activity was slower than that of the TAOC level. High concentrations of Cd or Phe had a stronger oxidative stress effect on Anadara subcrenata. Phe had a stronger effect on the SOD activity of Anadara subcrenata. The joint effects of Cd and Phe on the levels of ROS and TAOC, SOD activity and MDA content in Anadara subcrenata are dependent on their concentration combination, which were called the double-dose dependent effects and time-dependent effects, respectively. The binary mixture treatments of 477.33 μg/L Cd and 48.08 μg/L Phe had the highest oxidative stress on Anadara subcrenata.

De novo transcriptome analysis of stressed blood clam (Anadara broughtonii) and identification of genes associated with hemoglobin

BACKGROUND

Blood clam (Anadara broughtonii) is a commercially important marine bivalve characterised by the red blood. Recently, the clams have been subjected to severe resource recession. Multiple environmental stressors are indispensable for the recession.

OBJECTIVE

We aimed to investigate the transcriptome information of blood clam under environmental stressors.

METHODS

Paired-end Illumina HiSeq™ 2500 sequencing technology was employed for cDNA library construction and Illumina sequencing. Several public databases were introduced for gene annotation, and Kyoto Encyclopedia of Genes and Genomes (KEGG) database was used for pathways analyses. The Open Reading Frame of annotated hemoglobin (Hb) was predicted and validated by DNAMAN 6.0 and NCBI BLASTx, respectively.

RESULTS

A total of 242,919 transcripts were generated, 116,264 unigenes were subsequently assembled with an average length of 747 base pairs, and 33,776 unigenes were successfully annotated. Gene Ontology (GO) categories indicated that the terms of cellular processes, metabolic processes, cell, cell part, binding, and catalytic activity were dominant. KEGG pathway analyses suggested ribosome, oxytocin, focal adhesion, Ras, and PI3K-Akt were the largest signaling pathway groups, and many presented pathways (Ras, Rap1, and MAPK, etc.) were related to apoptosis, immune and stress response. In addition, a total of 19,306 potential simple sequence repeats (SSRs) were detected in 15,852 sequences. Six hemoglobin-related genes with complete conserved domain sequences were identified and 3 of them were predicted as HbI, HbIIα, and HbIIβ.

CONCLUSION

This study provides transcriptome responses to multiple environmental stressors in blood clams and would provide interesting hints for further studies.

The health risk for seafood consumers under future ocean acidification (OA) scenarios: OA alters bioaccumulation of three pollutants in an edible bivalve species through affecting the in vivo metabolism

The current knowledge about the effect of pCO₂-driven ocean acidification on the bioaccumulation of pollutants in marine species is still scarce, as only limited types of pollutants have been investigated. Therefore, to obtain a better understanding of the effect of ocean acidification on the process of bioaccumulation and subsequent food safety, the accumulation of benzo[a]pyrene (B[a]P), chloramphenicol (CAP), and nitrofurazone (NFZ) in an edible bivalve species, Tegillarca granosa, under present and near-future ocean acidification scenarios was investigated in the present study. The health risks associated with consuming contaminated blood clams were also assessed using target hazard quotient (THQ), lifetime cancer risk (CR), or margin of exposure (MoE). To explain the alterations in bioaccumulation of these pollutants, the expressions of genes encoding corresponding key metabolic proteins were analyzed as well. The results obtained showed that ocean acidification exerted a significant effect on the accumulation of B[a]P, NFZ, and CAP in the clams. After four-week exposure to B[a]P, NFZ, or CAP contaminated seawater acidified with CO₂ at pH 7.8 and 7.4, significantly greater amounts of B[a]P and lower amounts of NFZ and CAP were accumulated in the clams compared to that in the control. Although no non-carcinogenic risk of consuming B[a]P-contaminated blood clams was detected using the THQ values obtained, the CR values obtained indicated a high life-time risk in all groups. In addition, according to the MoE values obtained, the health risks in terms of consuming NFZ- and CAP-contaminated clams were significantly reduced under ocean acidification scenarios but still cannot be ignored, especially for children. The gene expression results showed that the ability of clams to eliminate B[a]P may be significantly constrained, whereas the ability to eliminate NFZ and CAP may be enhanced under ocean acidification scenarios, indicating that the changes in the accumulation of these pollutants may be due to the altered in vivo metabolism.

Allometric relationship in the bioaccumulation of radionuclides (134Cs &241Am) and delineation of contamination pathways (food and seawater) in bloody cockle Anadara senilis using radiotracer techniques

The uptake and depuration kinetics of ¹³⁴Cs and ²⁴¹Am were investigated in the bloody cockle Anadara senilis exposed via seawater and food in controlled conditions, using animals of different weight groups in order to assess how their bioaccumulation is affected by allometry and, hence, the individual's age. This study is one of the few experiments investigating bioaccumulation capacities of radionuclides in a West-African bivalve. Results showed that allometric relationships were mainly dependent on the exposure pathway considered. Significant relationships with body weight of bloody cockles were found during the uptake from dissolved phase for both radionuclides; they followed inverse power functions: smaller cockles concentrated both radionuclides more than larger ones. In contrast, radionuclide absorption and assimilation efficiencies from water and food, respectively, did not show any significant relationship with weight: only slight variation was observed between small and large organisms for the retention of ²⁴¹Am accumulated from food. A bioaccumulation model was used to assess the contribution of each pathway of exposure (food vs. water) in organisms grouped in small and large individuals. We found that, regardless of the size, ¹³⁴Cs was mainly bioaccumulated through the dietary pathway. In the case of ²⁴¹Am, the relative contribution of each pathway is weight-dependent: major contribution of dissolved pathway in smaller organisms and the major dietary contribution in larger organisms.

Transcriptome analysis of sex-related genes in the blood clam Tegillarca granosa

BACKGROUND

Blood clams (Tegillarca granosa) are one of the most commercial shellfish in China and South Asia with wide distribution in Indo-Pacific tropical to temperate estuaries. However, recent data indicate a decline in the germplasm of this species. Furthermore, the molecular mechanisms underpinning reproductive regulation remain unclear and information regarding genetic diversity is limited. Understanding the reproductive biology of shellfish is important in interpreting their embryology development, reproduction and population structure. Transcriptome sequencing (RNA-seq) rapidly obtains genetic sequence information from almost all transcripts of a particular tissue and currently represents the most prevalent and effective method for constructing genetic expression profiles.

RESULTS

Non-reference RNA-seq, an Illumina HiSeq2500 Solexa system, and de novo assembly were used to construct a gonadal expression profile of the blood clam. A total of 63.75 Gb of clean data, with at least 89.46% of Quality30 (Q30), were generated which was then combined into 214,440 transcripts and 125,673 unigenes with a mean length of 1,122.63 and 781.30 base pairs (bp). In total, 27,325 genes were annotated by comparison with public databases. Of these, 2,140 and 2,070 differentially expressed genes (DEGs) were obtained (T05 T08 vs T01 T02 T04, T06 T07 vs T01 T02 T04; in which T01-T04 and T05-T08 represent biological replicates of individual female and male clams, respectively) and classified into two groups according to the evaluation of biological replicates. Then 35 DEGs and 5 sex-related unigenes, in other similar species, were investigated using qRT-PCR, the results of which were confirmed to data arising from RNA-seq. Among the DEGs, sex-related genes were identified, including forkhead box L2 (Foxl2), sex determining region Y-box (Sox), beta-catenin (β-catenin), chromobox homolog (CBX) and Sex-lethal (Sxl). In addition, 6,283 simple sequence repeats (SSRs) and 614,710 single nucleotide polymorphisms (SNPs) were identified from the RNA-seq results.

CONCLUSIONS

This study provided the first complete gonadal transcriptome data for the blood clam and allowed us to search many aspects of gene sequence information, not limited to gender. This data will improve our understanding of the transcriptomics and reproductive biology of the blood clam. Furthermore, molecular markers such as SSRs and SNPs will be useful in the analysis of genetic evolution, bulked segregant analysis (BSA) and genome-wide association studies (GWAS). Our transcriptome data will therefore provide important genetic information for the breeding and conservation of germplasm.

Immunotoxicity of nanoparticle nTiO2 to a commercial marine bivalve species, Tegillarca granosa

The increasing production and extensive application of nanoparticles (NPs) inevitably leads to increased release of NPs into the marine environment and therefore poses a potential threat to marine organisms, especially the sessile benthic bivalves. However, the impacts of NPs on the immunity of commercial and ecological important bivalve species, Tegillarca granosa, still remain unknown to date. In addition, the molecular mechanism of the immunotoxicity of NPs still remains unclear in marine invertebrates. Therefore, the immunotoxicity of nTiO₂ exposure to T. granosa at environmental realistic concentrations was investigated in the present study. Results obtained showed that the total number, phagocytic activity, and red granulocytes ratio of the haemocytes were significantly reduced after 30 days nTiO₂ exposures at the concentrations of 10 and 100 μg/L. Furthermore, the expressions of genes encoding Pattern Recognition Receptors (PPRs) and downstream immune-related molecules were significantly down-regulated by nTiO₂ exposures, indicating a reduced sensitivity to pathogen challenges. In conclusion, evident immunotoxicity of nTiO₂ to T. granosa at environmental realistic concentrations was detected by the present study. In addition, the gene expression analysis suggests that the PRRs (both TLRs and RIG1 investigated) may be the molecules for NPs recognition in marine invertebrates.

[EFFECT OF FOOD DEPRIVATION ON TRANSFORMATION OF CAROTENOIDS IN THE BIVALVE MOLLUSC ANADARA KAGOSHIMENSIS (TOKUNAGA, 1906)]

The composition and content of carotenoids in tissues of Anadara kagoshimensis (Tokunaga, 1906) under conditions of food deprivation were analyzed over the interval of 30 days. By the end of the experiment a slight and uneven decrease of the level of total carotenoid content in tissues of foot, hepatopancreas, gills and in the sum of remaining tissues was observed. Initially β-carotene, pectenolon, zeaxanthin, diatoxanthin, alloxanthin and esters of the latter four carotenoids were found in tissues extracts. The qualitative composition of carotenoids in the examined tissues was similar. In the course of the experiment changes were noted in both the composition of carotenoids and their content. Changes common for all tissues were shown: β-carotene disappeared on days 3-4, over the interval of 30 days a decrease in the content of the esters of pectenolon, alloxanthin, zeaxanthin and diatoxanthin and an increase in the level of pectenolon and alloxanthin were observed. Tissue specificity was revealed: in foot and hepatopancreas tissues, at the background of decrease of the total content of esters of carotenoids, a considerable increase of pectenolon and alloxanthin concentration accompanied by an increase of diatoxanthin and zeaxanthin was observed; in gills and the sum of the remaining tissues, under similar increase in pectenolon and alloxanthin concentration, the level of diatoxanthin and zeaxanthin remained at the initial level or was even somewhat lower. The diagram of carotenod transformation is supplemented for Anadara kagoshimensis.

A preliminary study on the antibacterial mechanism of Tegillarca granosa hemoglobin by derived peptides and peroxidase activity

The blood clam, Tegillarca granosa, is one of the few bivalve molluscs containing hemoglobin (Hb). In the present study, we purified two types of T. granosa hemoglobin, Tg-HbI and Tg-HbII, using size exclusion chromatography and measured their antibacterial and peroxidase activities. We also tested antibacterial activities of peptides prepared by trypsin digestion of purified Tg-Hb and reversed-phase high-performance liquid chromatography purification. Purified Tg-HbI and Tg-HbII showed antibacterial activity against Escherichia coli, Pseudomonas putida, Bacillus subtilis, and Bacillus firmus, with differences in minimal inhibitory concentrations (MICs), but lacked antibacterial activity against Vibrio alginolyticus, Vibrio parahaemolyticus, Vibrio harveyi and Staphylococcus aureus. In contrast, 7 Tg-Hb derived peptides exhibited varying degrees of antibacterial activity against V. alginolyticus (MICs: 12-200 μg/ml), V. parahaemolyticus (11-100 μg/ml) and V. harveyi (1-200 μg/ml). The antibacterial activity of Hb derived peptides was confirmed by fluorescence microscopy. In addition, peroxidase activity was detected in Tg-HbI and Tg-HbII. The results indicated that in addition to functioning as a respiratory protein T. granosa hemoglobins likely play a role in host antibacterial defense probably via a peroxidase activity of native molecules and some internal peptides released from the proteins.

Gal/GalNAc specific multiple lectins in marine bivalve Anadara granosa

Complete lectin mapping of molluscs with their diversified recognition pattern and possible role in lectin-carbohydrate interaction based immune response triggering need much attention. In this communication, Gal/GalNAc specific three lectins AGL-IA (Anadara granosa lectin-IA), AGL-IB (A. granosa lectin-IB) and AGL-IV (A. granosa lectin-IV) and a lectin having hemolytic activity AGL-III (A. granosa lectin-III) were purified from the plasma of A. granosa bivalve by a combination of gel filtration and affinity chromatography. AGL-IA and IB were oligomeric lectins whereas, AGL-III and IV were monomeric. The molecular weight of AGL-IA, IB, III and IV were 375, 260, 45 and 33 kDa respectively. AGL-IA and IV agglutinated both rabbit and pronase treated human erythrocytes, whereas AGL-IB agglutinated only rabbit erythrocytes. AGL-III was found to agglutinate rabbit erythrocytes, however, it caused hemolysis of pronase treated human erythrocytes. The activity of all four lectins was calcium dependent and maximum at a pH range 7-8. Apart from Gal/GalNAc specific, the four lectins showed substantial differences in their carbohydrate recognition pattern. Moreover, there was a difference in the carbohydrate specificity between AGL-III and other three lectins (AGL-IA, AGL-IB and AGL-IV) towards polyvalent glycotope. On the one hand, 'cluster glycoside effect' i.e., an enhancement of the activity of a multivalent ligand, was observed for carbohydrate specificities of AGL-IA, AGL-IB, AGL-IV. On the other hand, the effect of multivalent ligands on the carbohydrate specificity of AGL-III was opposite of cluster glycoside effect. The affinity of AGL-IA, AGL-IB and AGL-IV for ligands can be ranked as follows: glycoproteins >> polysaccharide > oligosaccharides and monosaccharides. However, Gal related monosaccharides were the best inhibitors of AGL-III and the inhibitory activity decreased gradually in the following order: monosaccharide > disaccharide > polysaccharide. Thus, the diverse specificity of multiple lectins in A. granosa plasma possibly enables to recognize a wide range of microorganisms.

[ELEMENTS OF THE LOW MOLECULAR WEIGHT CHAIN OF ANTIOXIDANT DEFENSE IN TISSUES OF THE BLACK SEA MOLLUSC ANADARA KAGOSHIMENSIS BRUGÙIERE]

The content of reduced glutathione (GSH) and the activity of the coupled with it antioxidant enzymes - glutathione peroxidase and glutathione reductase as well the level of glucose, carbamide and amino acids were investigated in the hepatopancreas, gills and foot of the Black, Sea mollusk Anadara kagoshimensis. The highest content of GSH and the highest activity of glutathione peroxidase were found in mollusk foot, evidencing the active antioxidant role of glutathione played both within composition of this enzyme and independently. The maximal content of glucose, amino acids and carbamide was in the hepatopancreas and gills and the minimal - in the anadara's foot. The possible involvement and role of these low molecular weight antioxidants in the defense of mollusk tissues against action of free radical oxidation and in providing adaptation reactions of anadara in hypoxic habitats are considered. Key words: antioxidant complex, glutathione, glucose, carbamide, amino acids, anadara Anadara kagoshimensis, Black Sea.

Titanium dioxide nanoparticles as carrier facilitate bioaccumulation of phenanthrene in marine bivalve, ark shell (Scapharca subcrenata)

To evaluate the impact of titanium dioxide nanoparticles (nTiO2) on the uptake of hydrophobic organic chemicals by marine bivalves, we conducted a comparative bioaccumulation study by exposing clam, Scapharca subcrenata, to phenanthrene (Phe) in the presence and absence of nTiO2. The large surface area of nTiO2 resulted in adsorption of co-existing Phe in aqueous solution to form nTiO2-Phe complexes. Accumulation of nTiO2 was not observed in clams at exposed concentration (500 μg/L) in this study. However, enhanced uptake of Phe by clams was observed in the presence of nTiO2, with ku and BAFs values being 2 and 1.7 times higher than that of Phe alone, respectively. The enhanced uptake can be explained by ingestion of nTiO2-Phe complexes into the gut and subsequent desorption of Phe there. Therefore, nTiO2 as a carrier facilitated the uptake of Phe by marine bivalves.

Hemiuroid trematode sporocysts are undetected by hemocytes of their intermediate host, the ark cockle Anadara trapezia: potential role of surface carbohydrates in successful parasitism

In order to establish a successful relationship with their hosts, parasites must subvert or evade immune defences. Cockle Anadara trapezia and Sydney Rock oyster (SRO) Saccostrea glomerata live in the same location but only ark cockles are infected by sporocysts of hemiuroid trematode. This provides an opportunity to explore differing interactions between the parasite and the immune system of susceptible and refractive hosts. Rapid migration and encapsulation of sporocysts was observed by SRO hemocytes but not by cockle hemocytes. This migration/encapsulation was inhibited by N-acetylglucosamine or N-acetylgalactosamine but not by the other sugars, implicating specific surface carbohydrates in immune detection. Effector responses of hemocytes were investigated in vitro in terms of production of reactive oxygen production (ROS). Hemocytes of both species strongly reacted to Zymosan, but only SRO hemocytes responded to live sporocysts. Neither species' hemocytes produced ROS in the presence of dead/fixed sporocysts, and there was no suppression of Zymosan-induced respiratory burst by sporocysts. This suggests that immune escape is mediated by avoiding encapsulation, perhaps through molecular mimicry. Membrane-shaving with proteases indicated that sporocyst surface proteins are not a key factors in hemocytic detection. Surface carbohydrates of SRO and cockle hemocytes and of sporocysts were profiled with a panel of biotinylated lectins. This revealed substantial differences between cockle and SRO hemocytes, but greater similarity between cockle hemocytes and sporocysts. Results suggest that surface carbohydrates play an integral role in hemocyte immunorecognition and that surface carbohydrate molecular mimicry is a potential strategy for immune evasion in cockles by hemiuroid trematode sporocysts.

[Qualitative composition of carotenoids, catalase and superoxide dismutase activities in tissues of bivalve mollusc Anadara inaequivalvis (Bruguiere, 1789)]

By using high-performance liquid chromatography, UV-VIS-spectra and mass spectra (FAB MS) in tissues of bivalve mollusc Anadara inaequivalvis (Bruguiere, 1789) there are identified seven kinds of carotenoids: trans- and cis-pectenolon, alloxanthin, pectenol A, beta-carotene, zeaxanthin, and diatoxanthin. Their quantitative ratio in hepatopancreas, gills, and foot of the animals was determined. There was revealed negative correlation (R2 about 0.9) between content of several carotenoids (trans- and cis-pectenolon, zeaxanthin, alloxanthin, and diatoxanthin) in tissues and activities of antioxidant enzymes (catalase and superoxide dismutase). The presence of competitive relations between these molecular systems is assumed and their underlying causes are discussed.

Evaluation of the potential bioaccumulation ability of the blood cockle (Anadara granosa L.) for assessment of environmental matrices of mudflats

The spatial distribution of 19 polycyclic aromatic hydrocarbons (tPAHs) was quantified in aquacultures located in intertidal mudflats of the west coast of Peninsular Malaysia in order to investigate bioaccumulation of PAH in blood cockles, Anadara granosa (A. granosa). Fifty-four samples from environmental matrices and A. granosa were collected. The sampling locations were representative of a remote area as well as PAH-polluted areas. The relationship of increased background levels of PAH to anthropogenic PAH sources in the environment and their effects on bioaccumulation levels of A. granosa are investigated in this study. The levels of PAH in the most polluted station were found to be up to ten-fold higher than in remote areas in blood cockle. These high concentrations of PAHs reflected background contamination, which originates from distant airborne and waterborne transportation of contaminated particles. The fraction and source identification of PAHs, based on fate and transport considerations, showed a mix of petrogenic and pyrogenic sources. The relative biota-sediment accumulation factors (RBSAF), relative bioaccumulation factors from filtered water (RBAFw), and from suspended particulate matter (SPM) (RBAFSP) showed higher bioaccumulations of the lower molecular weight of PAHs (LMWs) in all stations, except Kuala Juru, which showed higher bioaccumulation of the higher molecular weight of PAHs (HMWs). Calculations of bioaccumulation factors showed that blood cockle can accumulate PAHs from sediment as well as water samples, based on the physico-chemical characteristics of habitat and behaviour of blood cockles. Correlations among concentrations of PAHs in water, SPM, sediment and A. granosa at the same sites were also found. Identification of PAH levels in different matrices showed that A. granosa can be used as a good biomonitor for LMW of PAHs and tPAHs in mudflats. Considering the toxicity and carcinogenicity of PAHs, the bioaccumulation by blood cockles are a potential hazard for both blood cockles and their consumers.

Accumulation profile and seasonal variations of polychlorinated biphenyls (PCBs) in bivalves Crassostrea tulipa (oysters) and Anadara senilis (mussels) at three different aquatic habitats in two seasons in Ghana

Research has shown that some polychlorinated biphenyl congeners degrade slowly in the environment and build up in the food chain, causing a wide range of possible adverse effects to humans. In order to ascertain the nature of the situation in Ghana, polychlorinated biphenyls congener residues in Crassostrea tulipa (oysters) and Anadara senilis (mussels) at Narkwa, Ada and Anyanui in the coastal region of Ghana were determined. At Narkwa, both bivalves' species were collected; at Ada only Anadara senilis were collected while at Anyanui, only Crassotrea tulipa were collected. The number of each bivalve species collected from each site was 80 (n=80), making up a total of 320 for the dry and the wet seasons. The PCBs were extracted with (1:1) hexane-acetone mixture and analyzed with a gas chromatogram equipped with (65)Ni electron capture detector, model CP 3800 using the mixed PCBs standard of the ICES 7. Total PCBs in the bivalves ranged from 5.55 to 6.37 μg/kg wet weight in mussels and 2.95-11.41 μg/kg wet weight in oysters, respectively. The composition of the PCB homologues in the bivalves was dominated by tri-, hepta- and hexa-PCBs in descending order. Risk assessments conducted on the samples indicated that edible bivalves from Narkwa, Ada and Anyanui in Ghana might pose some health risk to the consumers.

Exposure-dose-response of Anadara trapezia to metal contaminated estuarine sediments: 3. Selenium spiked sediments

Selenium enters near shore marine environments from the activities of coal-fired power stations. Although selenium is an essential element, at elevated concentrations it can cause genotoxic damage. The relationship between selenium exposure dose and response was investigated in Anadara trapezia exposed to selenium spiked sediment (5 μg/g and 20 μg/g dry mass) for 56 days. A. trapezia reached an equilibrium selenium tissue concentration (2 μg/g and 10 μg/g respectively) by day 42. Gills had significantly more selenium than the hepatopancreas and haemolymph. Between 12 and 21% of accumulated selenium in the gill and hepatopancreas was detoxified and in the metal rich granule. Most of the biologically active selenium in both tissues was in the mitochondrial fraction. Glutathione peroxidase activity and mean total glutathione concentrations for selenium exposed organisms were not significantly different to controls. The ratio of reduced to oxidised glutathione and the total antioxidant capacity were significantly reduced in selenium exposed organisms compared to control organisms. Increased selenium exposure resulted in significant increases in lipid peroxidation, lysosomal destabilisation and an increased frequency of micronuclei. A significant exposure-dose-response relationship for A. trapezia exposed to selenium enriched sediments indicates that elevated sediment selenium concentrations can increased biologically active selenium burdens and cause impairment of cellular processes and cell integrity.

A novel tissue inhibitor of metalloproteinase in blood clam Tegillarca granosa: molecular cloning, tissue distribution and expression analysis

Tissue inhibitor of metalloproteinases (TIMPs) were originally characterized as inhibitors of matrix metalloproteinases (MMPs), but their range of activities has been found to be broader as it includes the inhibition of several of the MMPs, etc. The cDNA encoding TIMP-4-like gene from blood clam Tegillarca granosa (designated as Tg-TIMP-4-like) which is the first tissue inhibitor of metalloproteinase identified in blood clams, was cloned and characterized. It was of 1164 bp, and an open reading frame (ORF) of 666 bp encoding a putative protein of 222 amino acids. The predicted amino acid sequence comprised all recognized functional domains found in other TIMP homologues and showed the highest (30.56%) identity to the TIMP-1.3 from Crassostrea gigas. Several highly conserved motifs including several TIMP signatures, amino acid residue Cys³⁰ responsible for coordinating the metal ions, the Cys-X-Cys motif and the putative NTR (netrin) domain were almost completely conserved in the deduced amino acid of Tg-TIMP-4 like, which indicated that Tg-TIMP-4-like should be a member of the TIMP family. The mRNA expression of Tg-TIMP-4-like in the tissues of mantle, adductor muscle, foot, gill, hemocyte and hepatopancreas was examined by quantitative real-time PCR (qT-PCR) and mRNA transcripts of Tg-TIMP-4-like were mainly detected in hemocyte, and weakly detected in the other tissues. We also observed that Tg-TIMP-4 like mRNA accumulated significantly during Vibrio parahaemolyticus, Peptidogylcan (PGN) and Lipopolysaccharide (LPS) challenge, whereas the timing and quantitative differences of mRNA expression against different challenge indicated that Tg-TIMP-4-like may play a pivotal role in mollusc defense mechanisms.

Effect of unialgal diets on the composition of fatty acids and sterols in juvenile ark shell Tegillarca granosa Linnaeus

This study has investigated the effects of six different unialgal diets ( Chaetoceros calcitrans , Platymonas helgolandica , Chlorella sp., Isochrysis galbana , Nannochloropsis oculata , and Pavlova viridis ) on the composition of fatty acids and sterols in juvenile ark shell Tegillarca granosa Linnaeus. The best feeding effects on the growth of shellfish were found in C. calcitrans, followed by I. galbana and P. viridis, whereas Chlorella sp. and N. oculata exhibited relatively poor effects. The fatty acid and sterol compositions in the six microalgae and the juvenile ark shell after feeding were analyzed, and 39 fatty acids and 18 sterols were identified. Although the results demonstrate a close correlation between the sterol compositions in algal species and juvenile ark shell, a similar correlation was not observed between fatty acids. In the juvenile ark shell fed microalgae, the ratio of total saturated fatty acids (SFA) rapidly decreases, whereas the proportion of total polyunsaturated fatty acids (PUFAs) increases considerably. The abundances of AA, EPA, and DHA increase most significantly in shellfish with better growth (fed C. calcitrans, I. galbana, and P. viridis). The number of sterol species is reduced, but the total sterol content in groups fed corresponding microalgae increases, and abundant plant sterols, instead of cholesterol, are accumulated in juvenile ark shell fed appropriate microalgae I. galbana and P. viridis. Therefore, to be more conducive to human health, I. galbana and P. viridis, of the six experimental microalgae, are recommended for artificial ark shell culture.

Exposure-dose-response of Anadara trapezia to metal contaminated estuarine sediments. 1. Cadmium spiked sediments

The relationship between cadmium exposure dose and response was investigated in Anadara trapezia exposed to cadmium spiked sediment (10 μg/g and 50 μg/g dry mass) for 56 days. A. trapezia reached an equilibrium cadmium tissue concentration (13 μg/g and 25 μg/g, respectively) by day 42. Gills accumulated significantly more cadmium than the hepatopancreas and haemolymph. After 56 days exposure between 46 and 73% of accumulated gill and hepatopancreas cadmium was detoxified and in the metallothionein like protein fraction. Approximately half of the biologically active cadmium in both tissues was in the mitochondrial fraction which has the potential to cause dysfunction in mitochondrial activity. Cadmium exposed A. trapezia generally had reduced GPx activity with an associated increase in total glutathione concentrations and reduced GSH:GSSG ratios due to a build up of oxidised glutathione. The changes in the glutathione pathway were reflected in the total antioxidant capacity of cadmium exposed A. trapezia which were significantly reduced compared to control organisms. There was a trend of increased lipid peroxidation with increased cadmium exposure but this was not significant. Increased cadmium exposure resulted in significant lysosomal destabilisation and increased frequency of micronuclei. The significant exposure-dose-response relationship for A. trapezia exposed to cadmium enriched sediments indicates that elevated sediment cadmium concentrations have the potential to lead to increased biologically active cadmium burdens and impairment of individual A. trapezia at cellular and subcellular levels.

[Peculiarities of organization of tissue metabolism in molluscs with different tolerance to external hypoxia]

Oxygen consumption, content of several carbohydrate metabolites, and activities of their coupled enzymes were studied in bivalve molluscs with different tolerance to oxygen deficit: Mytilus galloprovincialis Lam. (black morpha) and Anadara inaequivalvis Br. It has been shown that under conditions of external normoxia the anadara resistance to hypoxia preserves anaerobic orientation of metabolism. Its tissues are distinguished by high activities of malate and lactate dehydrogenases with the decreased content of glucose and the increased level of lactate. In several organs the succinate thiokinase and fumarate reductase reactions are realized, which is indicated by elevated activities of the alanine and aspartate aminotransferases. The anaerobic orientation of protein metabolism is added by a high pool of free aminoacids and the elevated urea content in the molluscs tissues. The total orientation of metabolism in the anadara tissues rules out a significant lactate accumulation and determines low requirements of its organism in oxygen.

Bioaccumulation and trophic transfer of polybrominated diphenyl ethers (PBDEs) in biota from the Pearl River Estuary, South China

Two hundred and fifty-four biota samples (four species of invertebrates and ten species of fish) were collected from the Pearl River Estuary between 2005 and 2007 and one hundred and twenty four individual or composite samples were analyzed for polybrominated diphenyl ethers (PBDEs). The concentrations of PBDEs in organisms varied from 6.2 to 208ng/g lipid weight. This PBDE level was significantly lower than those collected in 2004, showing a decreasing trend of PBDEs in biota in the study area. Trophic magnification factors (TMFs) for nine BDE congeners were calculated with values ranging from 0.78 to 3.0. TMFs of BDE47, 66, 100, 99, 154, and 153 were statistically greater than one, indicating a biomagnifcation potential for these congeners. Significant positive correlations were also found between concentrations of the total PBDEs, BDE28, 47, 66, 100, 99, 154, and153 and lipid content in biota, indicating the that bioconcentration also played an important role in the accumulation of PBDEs. No correlation between trophic level and lipid content was found, suggesting that biomagnification was not the result of lipid content effect but indeed occurred. The concentration ratios of BDE99 to BDE100 were much lower in biota than that in water implying that potential congener-specific biotransformation of PBDEs occurred and influenced the biomagnification of BDE congeners.

[Tissue specificity of metabolism in bivalve mollusc Anadara inaequivalvis Br. under conditions of experimental anoxia]

Peculiarities of the course of metabolic processes in tissues of the bivalve mollusc Anadara inaequivalvis Br. were studied under conditions of experimental anoxia. In the absence of oxygen, in gill and foot the protein catabolism processes were found to be enhanced; this led to a decrease of the protein content and to an increase of the free amino acid and urea levels. Predominantly hydrolyzed were low molecular peptides, which was indicated by a decrease of the cathepsin D activity on the background of a rise of the gamma-glutamyltranspeptidase activity. Anoxia was accompanied by enhancement of the succinate thiokinase and fumarate reductase reactions controlled by alanine and aspartate aminotransferases. They prevented accumulation of toxic lactate in tissues and allowed obtaining an additional macroerg resource. Metabolic processes in the mollusc hepatopancreas were oriented to production of amino acids.

The accumulation of Zn, Se, Cd, and Pb and physiological condition of Anadara trapezia transplanted to a contamination gradient in Lake Macquarie, New South Wales, Australia

The benthic bivalve, Anadara trapezia, was collected from a 'clean' reference site and transplanted along a suspected trace metal contamination gradient in Lake Macquarie, NSW. At monthly intervals, Zn, Se, Cd and Pb concentrations were measured in the surficial sediments and whole tissues of the cockle as well as their physiological condition (Scope for Growth). Zinc, Cd and Pb concentrations in sediments decreased together, southward, with the highest concentrations in the Cockle Bay area, suggesting that this is the main source of contamination. Zinc, Cd and Pb concentrations were near or above [ANZECC/ARMCANZ, 2000. National water quality management strategy paper 4. Australian and New Zealand Guidelines for Fresh and Marine Water Quality, Australian and New Zealand Conservation Council and Agriculture and Resource Management Council of Australia and New Zealand. pp. 3.5.-1-3.5-10] sediment quality guidelines at Cockle Creek, Warners Bay and Koorooa Bay. Significant differences in trace metal concentrations could not be attributed to grain size or Fe concentration differences. Se concentrations were highest in fine grain Fe rich sediments of Whiteheads Lagoon, and likely to be associated with power generation operations. Trace metal concentrations did not vary significantly over time. Zinc, Cd and Pb concentrations in the tissues of A. trapezia followed a similar pattern to that of sediments. Zinc and Pb concentrations in cockles and sediments were highly correlated, indicating significant exposure-dose relationships. Selenium concentrations in the tissues of A. trapezia were higher after transplantation to the lake, however, Se concentrations were similar in all transplanted cockles, indicating that Se in contaminated sediments is not the major source of Se to organisms. There was a decline in the physiological condition of A. trapezia transplanted to Lake Macquarie after a 90-day-period with marked differences in clearance rates and respiration rates at some locations and absorption efficiencies at all locations. The mean Scope for Growth value at the most contaminated location, Cockle Bay, was markedly lower than at other locations. A significant Zn exposure-dose response relationship indicates that Zn bioaccumulation is occurring in response to sediment contamination. A significant Cd exposure-response relationship indicates that Cd may be influencing the health of cockles. Significant Pb exposure-dose, exposure-response and dose-response relationships indicate that Pb probably is affecting the health of cockles in Lake Macquarie. Therefore, Zn, Cd and Pb concentrations in sediments are likely to be affecting the health of cockles in Lake Macquarie.