Perkinsus spp. Occurrence in South America: A review

Marine mollusk production is increasing worldwide, and this trend is being evidenced in South American countries, where several species of bivalves are produced, exploited, and traded. This activity brings benefits either for the ecosystem, as it is a less impactful and polluting than other aquaculture practices, and to coastal human communities, as it provides food and income. However, emergence of outbreaks by pathogens is a major concern and can put an entire developing sector at risk. Perkinsosis is a disease caused by Perkinsus spp. protozoans that affect mollusks worldwide. In this review we provide information on Perkinsus spp. among bivalves from South America. Infections by these parasites were only reported to date among coastal Atlantic bivalves of Argentina, Uruguay, and Brazil. The vast majority of cases and studies are reported from Brazil. We comprehensively review those results here. Finally, we suggest some considerations for future investigations that may expand our knowledge of these parasites.

New phosphodiesterase-4 inhibitors present airways relaxant activity in a guinea pig acute asthma model

Asthma is a disease characterized by chronic inflammation and hyper responsiveness of airways. We aimed to assess the relaxant potential of phosphodiesterase-4 (PDE4) inhibitors N-sulfonilhidrazonic derivatives on non-asthmatic and asthmatic guinea pig trachea. Firstly, guinea pigs were sensitized and challenged with ovalbumin, and then morphological, and contractile changes were evaluated resulting from asthma, followed by evaluation of relaxant effect of derivatives on guinea pig trachea and the cAMP levels measurement by ELISA. It has been evidenced hypertrophy of airway smooth muscle, inflammatory infiltrate, and vascular abnormalities. Moreover, only sensitized tracheal rings were responsive to OVA. Contractile response to histamine, but not to carbachol, was greater in sensitized animals, however the relaxant response to aminophylline and isoprenaline were the same in non-asthmatics and asthmatics. N-sulfonilhidrazonic derivatives presented equipotent relaxant action independent of epithelium, with exception of LASSBio-1850 that presented a low efficacy (< 50%) and LASSBio-1847 with a 4-fold higher potency on asthmatics. LASSBio-1847 relaxant curve was impaired in the presence of propranolol and potentiated by isoprenaline in both groups. Furthermore, relaxation was potentiated 54- and 4-fold by forskolin in non-asthmatics and asthmatics, respectively. Likewise, LASSBio-1847 potentiated relaxant curve of aminophylline 147- and 4-fold in both groups. The PKA inhibitor H-89 impaired the relaxant potency of the derivative. Finally, LASSBio-1847 increased tracheal intracellular cAMP levels similarly to rolipram, selective PDE4 inhibitor, in both animals. LASSBio-1847 showed to be promising to relax guinea pig trachea from non-sensitized and sensitized guinea pigs by activation of β2-adrenergic receptors/AC/cAMP pathway.

Morphological and functional characterization of the oyster Crassostrea gasar circulating hemocytes: Cell types and phagocytosis activity

Hemocytes are the circulating cells of the hemolymph of oysters and are responsible for numerous physiological functions, including immune defense. The oyster Crassostrea gasar is a native species inhabiting mangrove habitat and is of great commercial interest, cultured throughout the Brazilian coast, mainly in the north and northeast. Despite its commercial importance, little is known about its immunological aspects and defense cells, the hemocytes. This work aimed to morphologically characterize hemocytes of the oyster C. gasar and to study one of the main cellular defense response, phagocytosis, using light microscopy and flow cytometry. The results showed the presence of six hemocyte populations in C. gasar hemolymph. These comprise of large and small granulocytes, large and small hyalinocytes, blast-like cells and a rare type classified as vesicular or serous hemocytes. Hyalinocytes were highly abundant and the most heterogeneous cell population, while small granulocytes, along with vesicular hemocytes were the less abundant population. Hemocytes of C. gasar oysters demonstrated capabilities to phagocytose three different types of particles tested: zymosan A, latex particles and Escherichia coli, indicating a broad defense capacity. The zymosan A were the most engulfed particles, followed by beads, mainly phagocytized by granulocytes, the most phagocytic cells, and finally E. coli, which were the least phagocytized. This study is the first characterization of C. gasar oyster hemocytes and will support future studies that aim to understand the participation of different hemocyte types in defense responses against pathogens and/or environmental changes.

A novel role for Teneurin C-terminal Associated Peptide (TCAP) in the regulation of cardiac activity in the Sydney rock oyster, Saccostrea glomerata

Teneurin C-terminal associated peptide (TCAP) is an ancient bioactive peptide that is highly conserved in metazoans. TCAP administration reduces cellular and behavioural stress in vertebrate and urochordate models, yet despite numerous studies in higher animals, there is limited knowledge of its role in invertebrates. In particular, there are no studies on TCAP's effects on the heart of any metazoan, which is a critical organ in the stress response. We used the Sydney rock oyster (SRO) as an invertebrate model to investigate a potential role for sroTCAP in regulating cardiac activity, including during stress. sroTCAP is localized to the neural innervation network of the SRO heart, and suggested binding with various heart proteins related to metabolism and stress, including SOD, GAPDH and metabotropic glutamate receptor. Intramuscular injection of sroTCAP (10 pmol) significantly altered the expression of heart genes that are known to regulate remodelling processes under different conditions, and modulated several gene families responsible for stress mitigation. sroTCAP (1 and 10 pmol) was shown to cause transient bradycardia (heart rate was reduced by up to 63% and for up to 40 min post-administration), indicative of an unstressed state. In summary, this study has established a role for a TCAP in the regulation of cardiac activity through modulation of physiological and molecular components associated with energy conservation, stress and adaptation. This represents a novel function for TCAP and may have implications for higher-order metazoans.

Apoptotic and antioxidant effects in HCT-116 colorectal carcinoma cells by a spiro-acridine compound, AMTAC-06

BACKGROUND

Acridine compounds have been described as promising anticancer agents. Previous studies showed that (E)-1'-((4-chlorobenzylidene)amino)-5'-oxo-1',5'-dihydro-10H-spiro[acridine-9,2'-pyrrole]-4'-carbonitrile (AMTAC-06), a spiro-acridine compound, has antitumor activity on Ehrlich tumor and low toxicity. Herein, we investigated its antitumor effect against human cells in vitro.

METHODS

MTT assay was used to assess cytotoxicity of AMTAC-06 (3.125-200 µM) against tumor and non-tumor cells, and the half-maximal inhibitory concentration (IC₅₀) and the selectivity index (SI) were calculated. The effects on the cell cycle (propidium iodide-PI-staining), apoptosis (Annexin V-FITC/PI double staining by flow cytometry), and production of reactive oxygen species, ROS (DCFH assay) were also evaluated. Statistical analysis was achieved using ANOVA followed by Tukey's post-test.

RESULTS

AMTAC-06 showed higher cytotoxicity against colorectal carcinoma HCT-116 cells (IC₅₀: 12.62 µM). The SI showed that AMTAC-06 was more selective for HCT-116 cells (HaCaT SI: 1.41; PBMC SI: 0.62) than doxorubicin (HaCaT SI: 0.10; PBMC SI: 0.01). AMTAC-06 (15 and 30 µM) induced an increase in the sub-G1 peak (p < 0.000001) and cell cycle arrest in S phase (p = 0.003547). Moreover, treatment with this compound (15 and 30 µM) resulted in increased early (p < 0.000001) and late apoptotic cells (p < 0.000001). In addition, there was a reduction on ROS production (p < 0.000001).

CONCLUSIONS

AMTAC-06 presents anticancer activity against HCT-116 cells by regulating the cell cycle, inducing apoptosis and an antioxidant action.

Teneurin and TCAP Phylogeny and Physiology: Molecular Analysis, Immune Activity, and Transcriptomic Analysis of the Stress Response in the Sydney Rock Oyster (Saccostrea glomerata) Hemocytes

Teneurin C-terminal associated peptide (TCAP) is an ancient bioactive peptide that is highly conserved in metazoans. TCAP administration reduces cellular and behavioral stress in vertebrate and urochordate models. There is little information for invertebrates regarding the existence or function of a TCAP. This study used the Sydney rock oyster (SRO) as a molluscan model to characterize an invertebrate TCAP, from molecular gene analysis to its physiological effects associated with hemocyte phagocytosis. We report a single teneurin gene (and 4 teneurin splice variants), which encodes a precursor with TCAP that shares a vertebrate-like motif, and is similar to that of other molluscan classes (gastropod, cephalopod), arthropods and echinoderms. TCAP was identified in all SRO tissues using western blotting at 1-2 different molecular weights (~22 kDa and ~37kDa), supporting precursor cleavage variation. In SRO hemolymph, TCAP was spatially localized to the cytosol of hemocytes, and with particularly high density immunoreactivity in granules. Based on 'pull-down' assays, the SRO TCAP binds to GAPDH, suggesting that TCAP may protect cells from apoptosis under oxidative stress. Compared to sham injection, the intramuscular administration of TCAP (5 pmol) into oysters modulated their immune system by significantly reducing hemocyte phagocytosis under stress conditions (low salinity and high temperature). TCAP administration also significantly reduced hemocyte reactive oxygen species production at ambient conditions and after 48 h stress, compared to sham injection. Transcriptomic hemocyte analysis of stressed oysters administered with TCAP demonstrated significant changes in expression of genes associated with key metabolic, protective and immune functions. In summary, this study established a role for TCAP in oysters through modulation of physiological and molecular functions associated with energy conservation, stress and cellular defense.

Exposure to 2,4-D herbicide induces hepatotoxicity in zebrafish larvae

2,4-Dichlorophenoxyacetic acid (2,4-D) herbicide is the main ingredient in over 1500 commercially available products such as Weedestroy® AM40 and DMA® 4 IVM. Although the liver has been identified as one of the organs that are affected by this herbicide, reports on its hepatotoxic effects available in the literature are restricted to rats. Thus, there is a gap in information on other organisms that may be vulnerable to 2,4-D exposure, such as fish. Therefore, the present work aimed to assess the hepatotoxic potential of 2,4-D in fish using zebrafish (Danio rerio) larvae as a model system. For this purpose, its acute toxicity to zebrafish embryos was assessed, as well as its sublethal effects (< LC₅₀) on the activity of enzymes related to oxidative (GST, CAT and GPX) and metabolic (LDH) stress and liver parameters (AST, ALT and ALP) after 48 h of exposure. Morphological analyses of the liver were also assessed in zebrafish larvae. As a result, 2,4-D reduced larvae survival (LC₅₀ 15.010 mg/L in 96 h of exposure), induced malformations, altered the activity of LDH, GST and CAT enzymes and significantly increased the activity of all biomarkers for liver damage. Although no changes in the color or size of larval liver were observed, histopathological analysis revealed that treatment with 2,4-D caused severe changes in liver tissue, such as vacuolization of the cytosol, eccentric cell nucleus, loss of tissue architecture and cellular boundaries. Thus, the results showed that 2,4-D altered the enzymatic profile related to oxidative stress, and induces liver damage.

Identification of candidate microRNAs from Ostreid herpesvirus-1 (OsHV-1) and their potential role in the infection of Pacific oysters (Crassostrea gigas)

Oyster production is an economic activity of great interest worldwide. Recently, oysters have been suffering significant mortalities from OsHV-1infection, which has resulted in substantial economic loses in several countries around the world. Understanding viral pathogenicity mechanisms is of central importance for the establishment of disease control measures. Thus, the present work aimed to identify and characterize miRNAs from OsHV-1 as well as to predict their target transcripts in the virus and the host. OsHV-1 genome was used for the in silico discovery of pre-miRNAs. Subsequently, viral and host target transcripts of the OsHV-1 miRNAs were predicted according to the base pairing interaction between mature miRNAs and mRNA 3' untranslated regions (UTRs). Six unique pre-miRNAs were found in different regions of the viral genome, ranging in length from 85 to 172 nucleotides. A complex network of self-regulation of viral gene expression mediated by the miRNAs was identified. These sequences also seem to have a broad ability to regulate the expression of host immune-related genes, especially those associated with pathogen recognition. Our results suggest that OsHV-1 encodes miRNAs with important functions in the infection process, inducing self-regulation of viral transcripts, as well as affecting the regulation of Pacific oyster transcripts related to immunity. Understanding the molecular basis of host-pathogen interactions can help mitigate the recurrent events of oyster mass mortalities by OsHV-1 observed worldwide.

Effects of marine harmful algal blooms on bivalve cellular immunity and infectious diseases: A review

Bivalves were long thought to be "symptomless carriers" of marine microalgal toxins to human seafood consumers. In the past three decades, science has come to recognize that harmful algae and their toxins can be harmful to grazers, including bivalves. Indeed, studies have shown conclusively that some microalgal toxins function as active grazing deterrents. When responding to marine Harmful Algal Bloom (HAB) events, bivalves can reject toxic cells to minimize toxin and bioactive extracellular compound (BEC) exposure, or ingest and digest cells, incorporating nutritional components and toxins. Several studies have reported modulation of bivalve hemocyte variables in response to HAB exposure. Hemocytes are specialized cells involved in many functions in bivalves, particularly in immunological defense mechanisms. Hemocytes protect tissues by engulfing or encapsulating living pathogens and repair tissue damage caused by injury, poisoning, and infections through inflammatory processes. The effects of HAB exposure observed on bivalve cellular immune variables have raised the question of possible effects on susceptibility to infectious disease. As science has described a previously unrecognized diversity in microalgal bioactive substances, and also found a growing list of infectious diseases in bivalves, episodic reports of interactions between harmful algae and disease in bivalves have been published. Only recently, studies directed to understand the physiological and metabolic bases of these interactions have been undertaken. This review compiles evidence from studies of harmful algal effects upon bivalve shellfish that establishes a framework for recent efforts to understand how harmful algae can alter infectious disease, and particularly the fundamental role of cellular immunity, in modulating these interactions. Experimental studies reviewed here indicate that HABs can modulate bivalve-pathogen interactions in various ways, either by increasing bivalve susceptibility to disease or conversely by lessening infection proliferation or transmission. Alteration of immune defense and global physiological distress caused by HAB exposure have been the most frequent reasons identified for these effects on disease. Only few studies, however, have addressed these effects so far and a general pattern cannot be established. Other mechanisms are likely involved but are under-studied thus far and will need more attention in the future. In particular, the inhibition of bivalve filtration by HABs and direct interaction between HABs and infectious agents in the seawater likely interfere with pathogen transmission. The study of these interactions in the field and at the population level also are needed to establish the ecological and economical significance of the effects of HABs upon bivalve diseases. A more thorough understanding of these interactions will assist in development of more effective management of bivalve shellfisheries and aquaculture in oceans subjected to increasing HAB and disease pressures.

Impacts of the toxic benthic dinoflagellate Prorocentrum lima on the brown mussel Perna perna: Shell-valve closure response, immunology, and histopathology

Prorocentrum lima is a widely distributed marine benthic dinoflagellate that produces diarrhetic toxins, okadaic acid (OA) and its analogs, that may promote damage on bivalve tissues and cellular responses. Cultivation of the brown mussel Perna perna represents an important economic activity in the tropical and subtropical regions, where mussels may co-occur with P. lima. This study aimed to assess the behavioral, cellular immune responses, and pathological condition of P. perna following a short-term experimental exposure to P. lima. The toxic dinoflagellate treatment was compared to a non-toxic exposure to the chlorophyte Tetraselmis sp. at similar concentrations. The prevalence of pathological conditions and parasites were assessed, and a pathological index was applied by scoring the prevalences into four levels. Reaction time and the number of stimuli necessary for shell-valve closure response significantly increased after 72 h of P. lima exposure. Circulating hemocyte concentration was significantly lower in P. lima exposed mussels than in control mussels at 48- and 96 h of incubation, while hemocyte relative size in exposed mussels was significantly higher than that in control mussels. Comparatively, phagocytic activity and ROS production by hemocytes was significantly higher in mussels exposed to P. lima at 48- and 96 h of incubation, respectively. In addition, exposed mussels significantly presented exacerbated hemocytic infiltration in digestive organs, higher prevalence of moderate to severe atrophy in digestive tubules, and higher pathological index which suggests an impairment of mussel immunologic responses. A lower prevalence of Rickettsia-like organisms (RLOs), trematodes and copepods in P. lima exposed mussels suggests a direct toxic effect of OA on parasites. The exposure of mussels to P. lima is likely to occur frequently and may lead to constraints on mussel behavior, physiology, and pathological condition.

Disseminated neoplasia in cultured Crassostrea gasar oysters from northeast Brazil

Disseminated neoplasia (DN) is a disease that affects bivalves worldwide and can lead to mass mortalities. In the present study, a pathological survey conducted from December 2011 to August 2012 in Crassostrea gasar, an oyster of commercial interest in northeast Brazil, revealed the occurrence of DN in oysters reared in the Mamanguape estuary, Paraíba State, Brazil. The present work describes the pathological and functional aspects of the disease in C. gasar by light microscopy (haemolymph cell monolayer and histological section) and flow cytometry analyses. The prevalence of the disease was low (7.1% of 182 oysters examined). Enlarged (neoplastic) cells showed reniform, ovoid or circular-shaped nuclei, with prominent nucleoli and predominantly short filipodia. They were found in the haemolymph and infiltrated the connective tissues of different organs, including the digestive system, gills and gonads, as well as in the sinuses and vessels. Three levels of progression of DN in tissues were observed, light (61.5%), moderate (15.4%) and advanced (23.1%). The viability of neoplastic cells circulating in the haemolymph (97.4%) was similar to that in the haemocytes (95.7%). The neoplastic cells showed low phagocytic ability (3.9%) compared with that of haemocytes (42.4%). Conversely, reactive oxygen species production (679 A.U.) and the total haemocyte count (3.9 × 10⁶ cells mL^-1) were higher in the affected oysters than in unaffected oysters (268 A.U. and 1.5 × 10⁶ cells mL^-1, respectively). The low prevalence and primarily mild intensity found in the sampled oysters does not preclude an impact at the population level. A timely survey of DN is thus recommended in order to assess the severity and impact of this disease in wild and cultured populations of C. gasar oysters.

Effect of antiprotozoal molecules on hypnospores of Perkinsus spp. parasite

Perkinsus protozoan parasites have been associated with high mortality of bivalves worldwide, including Brazil. The use of antiproliferative drugs to treat the Perkinsosis is an unusual prophylactic strategy. However, because of their environment impact it could be used to control parasite proliferation in closed system, such as hatchery. This study evaluated the anti-Perkinsus activity potential of synthesized and commercial compounds. Viability of hypnospores of Perkinsus spp. was assessed in vitro. Cells were incubated with three 2-amino-thiophene (6AMD, 6CN, 5CN) and one acylhydrazone derivatives (AMZ-DCL), at the concentrations of 31.25; 62.5; 125; 250 and 500 μM and one commercial chlorinated phenoxy phenol derivative, triclosan (2, 5, 10 and 20 μM), for 24-48 h. Two synthetic molecules (6CN and AMZ-DCL) caused a significant decline (38 and 39%, respectively) in hypnospores viability, at the highest concentration (500 μM), after 48 h. Triclosan was the most cytotoxic compound, causing 100% of mortality at 20 μM after 24 h and at 10 μM after 48 h. Cytotoxic effects of the compounds 6CN, AMZ-DCL, and triclosan were investigated by measuring parasite's zoosporulation, morphological changes and metabolic activities (esterase activity, production of reactive oxygen species and lipid content). Results showed that zoosporulation occurred in few cell. Triclosan caused changes in the morphology of hypnospores. The 6CN and AMZ-DCL did not alter the metabolic activities studied whilst Triclosan significantly increased the production of reactive oxygen species and changed the amount and distribution of lipids in the hypnospores. These results suggest that three compounds had potential to be used as antiprotozoal drugs, although further investigation of their mechanism of action must be enlightened.

Growth, mortality and susceptibility of oyster Crassostrea spp. to Perkinsus spp. infection during on growing in northeast Brazil

Abstract Crassostrea rhizophorae and C. gasar oysters are cultivated in the northeast region. Perkinsus parasites infect bivalves, and their effects on oysters from tropical regions are poorly understood. This study evaluated the impact of Perkinsus infection on the productive traits of native oysters. Oysters were sampled bimonthly during 7 months, from July 2010 to February 2011, to evaluate growth rate, mortality and shell color patterns (white and dark-gray) (n = 500), and to determine the prevalence and intensity of Perkinsus (n = 152). Perkinsus and Crassostrea species were determined using molecular tools. Results showed that most dark-gray (90%, n = 20) and white (67%, n = 18) oysters were C. gasar and C. rhizophorae, respectively. Oysters showed a high growth rate and moderate cumulative mortality (44%). C. gasar oysters grew better and showed lower mortality and lower incidence of Perkinsus compared to C. rhizophorae. The mean prevalence of Perkinsus was moderate (48%), but the infection intensity was light (2.2). Perkinsosis affected very small oysters (19.4 mm). In conclusion, native oysters, especially C. gasar, have a great potential for culture, mortality is not associated with perkinsosis, and the shell color of oysters can be used to improve selection for spats with better performance.

ABCB1 and ABCC1-like transporters in immune system cells from sea urchins Echinometra lucunter and Echinus esculentus and oysters Crassostrea gasar and Crassostrea gigas

ABC transporters activity and expression have been associated with the multixenobiotic resistance phenotype (MXR). The activity of these proteins leads to a reduction in the intracellular concentration of several xenobiotics, thus reducing their toxicity. However, little attention has been given to the expression of ABC transporters in marine invertebrates and few studies have investigated their role in immune system cells of sea urchins and shellfish bivalves. The aim of the present study was to investigate the activity of the ABC transporters ABCB1 and ABCC1 in immune system cells of sea urchins (coelomocytes) and oysters (hemocytes) from different climatic regions (Brazil and France). Sea urchins and oysters were collected at Paraíba coast; Brazil (Echinometra lucunter and Crassostrea gasar) and Rade of Brest; France (Echinus esculentus and Crassostrea gigas). Coelomocytes and hemocytes were stained with the ABC transporter substrate calcein-AM and dye accumulation analyzed under flow cytometry. Reversin 205 (ABCB1 transporter blocker) and MK571 (ABCC1 transporter blocker) were used as pharmacological tools to investigate ABC transporter activity. A different pattern of calcein accumulation was observed in coelomocytes: phagocytes > colorless spherulocytes > vibrate cells > red spherulocytes. The treatment with MK571 increased calcein fluorescence levels in coelomocytes from both species. However, reversin 205 treatment was not able to increase calcein fluorescence in E. esculentus coelomocytes. These data suggest that ABCC1-like transporter activity is present in both sea urchin species, but ABCB1-like transporter activity might only be present in E. lucunter coelomocytes. The activity of ABCC1-like transporter was observed in all cell types from both bivalve species. However, reversin 205 only increased calcein accumulation in hyalinocytes of the oyster C. gasar, suggesting the absence of ABCB1-like transporter activity in all other cell types, including hyalinocytes from the oyster C. gigas. Additionally, our results showed that C. gigas exhibited higher activity of ABCC1-like transporter in all hemocyte types than C. gasar. The present work is the first to characterize ABCB1 and ABCC1-like transporter activity in the immune system cells of sea urchins E. lucunter and E. esculentus and oysters. Our findings encourage the performing studies regarding ABC transporters activity/expression in immune system cells form marine invertebrates under stress conditions and the possible use of ABC transporters as biomarkers.

Perkinsus infection is associated with alterations in the level of global DNA methylation of gills and gastrointestinal tract of the oyster Crassostrea gasar

Bivalves are filter feeders that obtain food from seawater that may contain infectious agents, such as the protozoan parasites Perkinsus marinus and P. olseni that are associated with massive mortalities responsible for losses in the aquaculture industry. Despite all physical and chemical barriers, microorganisms cross epithelia and infect host tissues to cause pathologies. Epigenetics mechanisms play important roles in a variety of human processes, from embryonic development to cell differentiation and growth. It is currently emerging as crucial mechanism involved in modulation of host-parasite interactions and pathogenesis, promoting discovery of targets for drug treatment. In bivalves, little is known about epigenetic mechanism in host parasite interactions. The objective of the present study was to evaluate the effect of Perkinsus sp. infections on DNA methylation levels in tissues of Crassostrea gasar oysters. Samples were collected in 2015 and 2016 in the Mamanguape River estuary (PB). Oyster gills were removed and used for Perkinsus sp.

DIAGNOSIS

Gills (G) and gastrointestinal tract (GT), as well as cultured P. marinus trophozoites were preserved in 95% ethanol for DNA extractions. DNA methylation levels were estimated from G and GT tissues of uninfected (n=60) and infected oysters (n=60), and from P. marinus trophozoites, by ELISA assays. Results showed that the mean prevalence of Perkinsus sp. infections was high (87.3%) in 2015 and moderate (59.6%) in 2016. DNA methylation levels of G and GT tissues were significantly lower in infected oyster than in uninfected oysters, suggesting that infections are associated with hypomethylation. Methylation level was significantly higher in G than in GT tissues, indicating a likely tissue-specific mechanism. P. marinus trophozoites showed 33% methylation. This was the first study that confirms alterations of DNA methylation in two tissues of C. gasar oysters in association with Perkinsus sp. infections.

Effects of cyanobacteria Synechocystis spp. in the host-parasite model Crassostrea gasar-Perkinsus marinus

Perkinsosis is a disease caused by protozoan parasites from the Perkinsus genus. In Brazil, two species, P. beihaiensis and P. marinus, are frequently found infecting native oysters (Crassostrea gasar and C. rhizophorae) from cultured and wild populations in several states of the Northeast region. The impacts of this disease in bivalves from Brazil, as well as the interactions with environmental factors, are poorly studied. In the present work, we evaluated the in vitro effects of the cyanobacteria Synechocystis spp. on trophozoites of P. marinus and haemocytes of C. gasar. Four cyanobacteria strains isolated from the Northeast Brazilian coast were used as whole cultures (WCs) and extracellular products (ECPs). Trophozoites of P. marinus were exposed for short (4h) and long (48h and 7days, the latter only for ECPs) periods, while haemocytes were exposed for a short period (4h). Cellular and immune parameters, i.e. cell viability, cell count, reactive oxygen species production (ROS) and phagocytosis of inert (latex beads) and biological particles (zymosan and trophozoites of P. marinus) were measured by flow cytometry. The viability of P. marinus trophozoites was improved in response to WCs of Synechocystis spp., which could be a beneficial effect of the cyanobacteria providing nutrients and reducing reactive oxygen species. Long-term exposure of trophozoites to ECPs of cyanobacteria did not modify in vitro cell proliferation nor viability. In contrast, C. gasar haemocytes showed a reduction in cell viability when exposed to WCs, but not to ECPs. However, ROS production was not altered. Haemocyte ability to engulf latex particles was reduced when exposed mainly to ECPs of cyanobacteria; while neither the WCs nor the ECPs modified phagocytosis of the biological particles, zymosan and P. marinus. Our results suggest a negative effect of cyanobacteria from the Synechocystis genus on host immune cells, in contrast to a more beneficial effect on the parasite cell, which could together disrupt the balance of the host-parasite interaction and make oysters more susceptible to P. marinus as well as opportunistic infections.

Epizootiology of Perkinsus sp. inCrassostrea gasar oysters in polyculture with shrimps in northeastern Brazil

Abstract Bivalve culture is of considerable economic and social interest in northeastern (NE) Brazil. The polyculture is an alternative approach to traditional monoculture for reducing the environmental impact of shrimp farming and improving oyster culture. Perkinsus marinus andPerkinsus olseni were found infecting oysters in NE Brazil and can threaten oyster production. This study evaluatedPerkinsus spp. occurrence in Crassostrea gasar during all production stages. Oyster spats were produced in a hatchery and grown in shrimp ponds in Rio Grande do Norte state.Perkinsus spp. were surveyed by Ray’s fluid thioglycollate medium and confirmed by polymerase chain reaction. Prevalence and intensity of infection were determined in oysters until they reached 7 cm. Results showed that the broodstock was already infected by Perkinsus (60%), but the derived spats were Perkinsus-free. Oyster spats acquired Perkinsus infection when transferred to ponds. The prevalence gradually increased in the seven months following placement in ponds (73%), and then decreased to 17% by the tenth month. The infections were initially mild, but intensity increased at the final growth stage. In conclusion, it is possible to produce Perkinsus-free C. gasar oyster spats from infected broodstock, and their culture in shrimp ponds is feasible.

Physiological responses of Manila clams Venerupis (=Ruditapes) philippinarum with varying parasite Perkinsus olseni burden to toxic algal Alexandrium ostenfeldii exposure

Manila clam stock from Arcachon Bay, France, is declining, as is commercial harvest. To understand the role of environmental biotic interactions in this decrease, effects of a toxic dinoflagellate, Alexandrium ostenfeldii, which blooms regularly in Arcachon bay, and the interaction with perkinsosis on clam physiology were investigated. Manila clams from Arcachon Bay, with variable natural levels of perkinsosis, were exposed for seven days to a mix of the nutritious microalga T-Iso and the toxic dinoflagellate A. ostenfeldii, a producer of spirolides, followed by seven days of depuration fed only T-Iso. Following sacrifice and quantification of protozoan parasite Perkinsus olseni burden, clams were divided into two groups according to intensity of the infection ("Light-Moderate" and "Moderate-Heavy"). Hemocyte and plasma responses, digestive enzyme activities, antioxidant enzyme activities in gills, and histopathological responses were analyzed. Reactive oxygen species (ROS) production in hemocytes and catalase (CAT) activity in gills increased with P. olseni intensity of infection in control clams fed T-Iso, but did not vary among A. ostenfeldii-exposed clams. Exposure to A. ostenfeldii caused tissue alterations associated with an inflammatory response and modifications in hemocyte morphology. In the gills, superoxide dismutase (SOD) activity decreased, and an increase in brown cell occurrence was seen, suggesting oxidative stress. Observations of hemocytes and brown cells in tissues during exposure and depuration suggest involvement of both cell types in detoxication processes. Results suggest that exposure to A. ostenfeldii disrupted the pro-/anti-oxidant response of clams to heavy P. olseni intensity. In addition, depressed mitochondrial membrane potential (MMP) in hemocytes of clams exposed to A. ostenfeldii suggests that mitochondrial functions are regulated to maintain homeostasis of digestive enzyme activity and condition index.

Immunological responses of the mangrove oysters Crassostrea gasar naturally infected by Perkinsus sp. in the Mamanguape Estuary, Paraíba state (Northeastern, Brazil)

Perkinsus genus includes protozoan parasites of marine mollusks, especially bivalves. In the last four years, this parasite has been detected in mangrove oysters Crassostrea rhizophorae and Crassostrea gasar from the Northeastern region of Brazil. Hemocytes are the key cells of the oyster immune system, being responsible for a variety of cellular and humoral reactions, such as phagocytosis, encapsulation and the release of several effector molecules that control the invasion and proliferation of microorganisms. In Brazil, there is little information on perkinsosis and none on the immune responses of native oysters' species against Perkinsus spp. The objective of this study was to determine the effects of natural infection by Perkinsus sp. on the immunological parameters of mangrove oysters C. gasar cultured in the Mamanguape River Estuary (Paraíba, Brazil). Adults oysters (N = 40/month) were sampled in December 2011, March, May, August and October 2012. Gills were removed and used to determine the presence and intensity of the Perkinsus sp. infection, according to a scale of four levels (1-4), using the Ray's fluid thioglycollate medium assay. Immunological parameters were measured in hemolymph samples by flow cytometry, including: total hemocyte count (THC), differential hemocyte count (DHC), cell mortality, phagocytic capacity, and production of Reactive Oxygen Species (ROS). The plasma was used to determine the hemagglutination activity. The results showed the occurrence of Perkinsus sp. with the highest mean prevalence (93.3%) seen so far in oyster populations in Brazil. Despite that, no oyster mortality was associated. In contrast, we observed an increase in hemocyte mortality and a suppression of two of the main defense mechanisms, phagocytosis and ROS production in infected oysters. The increase in the percentage of blast-like cells on the hemolymph, and the increase in THC in oysters heavily infected (at the maximum intensity, 4) suggest an induction of hemocytes proliferation. The immunological parameters varied over the studied months, which may be attributed to the dynamics of infection by Perkinsus sp. The results of the present study demonstrate that Perkinsus sp. has a deleterious effect on C. gasar immune system, mainly in high intensities, which likely renders oysters more susceptible to other pathogens and diseases.

Effect of acclimatization on hemocyte functional characteristics of the Pacific oyster (Crassostrea gigas) and carpet shell clam (Ruditapes decussatus)

Most experimental procedures on molluscs are done after acclimatization of wild animals to lab conditions. Similarly, short-term acclimation is often unavoidable in a field survey when biological analysis cannot be done within the day of sample collection. However, acclimatization can affect the general physiological condition and particularly the immune cell responses of molluscs. Our aim was to study the changes in the hemocyte characteristics of the Pacific oyster Crassostrea gigas and the carpet shell clam Ruditapes decussatus acclimated 1 or 2 days under emersed conditions at 14 ± 1 °C and for 1, 2, 7, or 10 days to flowing seawater conditions (submerged) at 9 ± 1 °C, when compared to hemolymph withdrawn from organisms sampled in the field and immediately analyzed in the laboratory (unacclimated). The hemocyte characteristics assessed by flow cytometry were the total (THC) and differential hemocyte count, percentage of dead cells, phagocytosis, and reactive oxygen species (ROS) production. Dead hemocytes were lower in oysters acclimated both in emersed and submerged conditions (1%-5%) compared to those sampled in the field (7%). Compared to oysters, the percentage of dead hemocytes was lower in clams (0.4% vs. 1.1%) and showed a tendency to decrease during acclimatization in both emersed and submerged conditions. In comparison to organisms not acclimated, the phagocytosis of hemocytes decreased in both oysters and clams acclimated under submerged conditions, but was similar in those acclimated in emersed conditions. The ROS production remained stable in both oysters and clams acclimated in emersed conditions, whereas in submerged conditions ROS production did not change in both the hyalinocytes and granulocytes of oysters, but increased in clams. In oysters, the THC decreased when they were acclimated 1 and 2 days in submerged conditions and was mainly caused by a decrease in granulocytes, but the decrease in THC in oysters acclimated 2 days in emersed conditions was caused by a decrease in hyalinocytes and small agranular cells. In clams, the THC was significantly lower in comparison to those not acclimated, regardless of the conditions of the acclimatization. These findings demonstrate that hemocyte characteristics were differentially affected in both species by the tested conditions of acclimatization. The phagocytosis and ROS production in clams and phagocytosis in oysters were not different in those acclimated for 1 day under both conditions, i.e. emersed and submerged, and those sampled in the field (unacclimated). The THC was significantly affected by acclimatization conditions, so the differences between clams and oysters should be considered in studies where important concentrations of hemocytes are required. The difference in the immune response between both species could be related to their habitat (epifaunal vs. infaunal) and their ability of resilience to manipulation and adaptation to captivity. Our results suggest that functional characteristics of hemocytes should be analyzed in both oysters and clams during the first 1 or 2 days, preferably acclimated under emersed rather than submerged conditions.

First report of Perkinsus sp. infecting mangrove oysters Crassostrea rhizophorae from the Brazilian coast

Protozoan parasites of the genus Perkinsus are considered important pathogens responsible for mass mortalities in several mollusk species worldwide. In the present study we describe for the first time a parasite of the genus Perkinsus infecting the mangrove oyster Crassostrea rhizophorae from the Brazilian coast. Prevalence of this parasite was low in the Pacoti River estuary (Ceará, northeast Brazil) and absent in oysters from southern Brazil. Oyster gill and rectum tissues incubated in Ray's fluid thioglycollate medium (RFTM) revealed the presence of spherical hypnospores (5 to 55 microm diam.). Histological analysis showed the occurrence of typical signet-ring trophozoites and schizonts (3 to 6 microm diam.) infecting connective tissues of several organs and digestive epithelia. PCR assays specific to the genus Perkinsus, followed by cloning and sequencing of the internal transcribed spacer (ITS) region of the ribosomal ribonucleic acid (rRNA) gene complex, confirmed a close phylogenetic relationship between Brazilian Perkinsus sp. and P. beihaiensis infecting Chinese oysters.

Variability of haemocyte and haemolymph parameters in European flat oyster Ostrea edulis families obtained from brood stocks of different geographical origins and relation with infection by the protozoan Bonamia ostreae

A research project to compare productive traits (growth and mortality), disease susceptibility and immune capability between Ostrea edulis stocks was performed. This article reports the results on the immune capability and its relation with infection by the intrahaemocytic protozoan Bonamia ostreae. Four to five oyster spat families were produced from each of four European flat oyster populations (one from Ireland, one from Greece and two from Galicia, Spain) in a hatchery. The spat were transferred to a raft in the Ría de Arousa (Galicia) for on growing for 2 years. Total haemocyte count (THC) and differential haemocyte count (DHC) were estimated monthly through the second year of growing-out. Three types of haemocytes were distinguished: granulocytes (GH), large hyalinocytes (LHH) and small hyalinocytes (SHH). Significant correlations between the mean relative abundance of GH and SHH of the families and the mean prevalence of B. ostreae, the overall incidence of pathological conditions and the cumulative mortality of the families were found; these correlations supported the hypothesis that high %GH and low %SHH would enhance oyster immune ability and, consequently, would contribute to lower susceptibility to disease and longer lifespan. Infection by B. ostreae involved a significant increase of circulating haemocytes, which affected more markedly the LHH type. The higher the infection intensity the higher the %LHH. This illustrates the ability of B. ostreae to modulate the immune responses of the O. edulis to favour its own multiplication. A significant reduction of the phenoloxidase activity in the haemolymph of oysters O. edulis infected by B. ostreae was observed. Nineteen enzymatic activities in the haemolymph of O. edulis and Crassostrea gigas (used as a B. ostreae resistant reference) were measured using the kit api ZYM, Biomerieux. Qualitative and quantitative differences in enzyme activities in both haemocyte and plasma fractions between B. ostreae noninfected O. edulis from different origins were recorded. However, no clear positive association between enzyme activity and susceptibility to bonamiosis was found. The only enzyme detected in the resistant species C. gigas that was not found in the susceptible one O. edulis was beta-glucosidase (in plasma). B. ostreae infected O. edulis showed significant increase of some enzyme activities and the occurrence of enzymes that were not detected in noninfected oysters. These changes could be due to infection-induced enzyme synthesis by the host or to enzyme synthesis by the parasite.

Morphologic, cytometric and functional characterisation of abalone (Haliotis tuberculata) haemocytes

This work presents the first detailed microscopic and functional analysis of the haemocytes of an abalone; the European Haliotis tuberculata. It is shown that in contrast to the situation in bivalves, only very few basophilic "granulocytes" could be found and exclusively with a histological stain. Neither flow cytometry, phase contrast observation nor transmission electron microscopy were able to detect any granular cells. The large majority of cells was constituted of "hyalinocytes", which could be sorted by flow cytometry, for the first time, into small (blast-like) and large cells. This permits a detailed analysis of haemocytes and especially of the lowly represented blast-like cells. The differences in haemolymph cell composition between bivalves and gastropods is reviewed in depth and discussed in view of the new data we present. Most of the abalone haemocytes analysed harbour many vacuoles, large glycogen deposits, lipid inclusions and acidic compartments. However, although the number of these "inclusions" was rather variable in between individual hyalinocytes, these experiments did not allow to discern subpopulations using these criteria, and the population appears more as a "differentiation continuum". Haemocytes adhere very rapidly and are immunologically active as they quickly phagocytose latex beads and zymozan particles. This study is the first step towards understanding the H. tuberculata immune system by adapting new tools to gastropods and in providing a first detailed morpho-functional study of their haemocytes.

Hemocyte responses of Manila clams, Ruditapes philippinarum, with varying parasite, Perkinsus olseni, severity to toxic-algal exposures

This study assessed the possible combined effects of harmful algae and parasite infection on hemocyte and hemolymph parameters of a bivalve mollusc. Manila clams Ruditapes philippinarum, were exposed for 1 week, under controlled laboratory conditions, to bloom concentrations of two cultured dinoflagellates: Karenia selliformis, and Karenia mikimotoi, with demonstrated, sub-lethal, pathological effects upon these bivalves. Each dinoflagellate treatment was added to a basal diet of Chaetoceros neogracile; controls consisted of clams fed only C. neogracile. Hemocyte characteristics measured with flow-cytometric analyses, and agglutination titer, condition index, and prevalence and intensity of Perkinsus olseni, were assessed for individual clams before and after 3 and 6 days of microalgal exposure. Multifactor analysis of variance tests were conducted to determine possible effects of the harmful algae, time of exposure, and P. olseni intensity, as well as interactions between these three factors, upon each physiological variable measured. There was no relationship between P. olseni intensity and hemolymph measures. Both Karenia species, however, had a significant effect upon hemocyte profiles of the clams, and this effect was dependent upon duration of exposure; 3 days of exposure to the dinoflagellates generally was sufficient to resolve the effects on the clams. K. selliformis had a stronger effect than K. mikimotoi, which was intermediate between K. selliformis and clams fed the non-toxic control, C. neogracile. Total hemocyte counts increased in clams exposed to the harmful algae, while the percentage of dead hemocytes, as well as hemocyte size and complexity, decreased. Furthermore, these immunomodulating effects of K. selliformis were significantly more extreme in clams with a high parasite burden, compared with lightly infected clams. This report is, to our knowledge, the first study assessing the combined effects of harmful algae and parasite infection on a physiological function (hemocyte and hemolymph parameters) of a bivalve mollusc. These findings demonstrate that clams maintain hemocyte function when infected with P. olseni, that the clam immune system responds to harmful or toxic algal exposure, and that this response is modified by parasite infection.

Flow cytometric DNA content analysis of neoplastic cells in haemolymph of the cockle Cerastoderma edule

Epizootiological outbreaks of disseminated neoplasia (DN) have been reported in association with mass mortalities in various bivalve species including the cockle Cerastoderma edule. A flow cytometric (FCM) procedure to study DNA content was successfully adapted and tested in haemolymph cells (haemocytes and neoplastic cells) of the cockle. The FCM results were similar to those obtained by histological analysis (DN diagnosis and haemolymph cell features). FCM analysis revealed differences in DNA content among normal haemocytes (diploid) and neoplastic cells. Four types of cells with abnormal DNA content were found in the haemolymph of affected animals: hypodiploid, hyperdiploid, triploid-sesploid and pentaploid. Our results suggest that the flow cytometric DNA content analysis can be applied to identify neoplastic cell types and to study the association between different cell types and the DN progression or remission in this edible and commercially important bivalve species.