41 resultados para Dinoflagellate Gambierdiscus-toxicus


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Caribbean ciguatoxins (C-CTXs) are responsible for the widespread occurrence of ciguatera in the Caribbean Sea. The structure and configuration of C-CTX-1 (1), the major ciguatoxin isolated from the horse-eye jack (Caranx latus), has been determined from DQF-COSY, E-COSY, TOCSY, NOESY, POESY, ge-HSQC. and HMQC experiments performed at 750 MHz and 500 MHz on a 0.13 pmol sample. C-CTX-1 ([M + H](+) m/z 1141.6 Da, molecular formula C62H92O19) has a ciguatoxin/breveroxin ladder structure comprising 14 trans-fused, ether-linked rings (7/6/6/7/8/9/7/6/8/6/7/6/7/6) assembled fi um 6 protonated fragments. The relative stereochemistry and ring configuration of 1 was determined from an analysis of coupling constant and NOE data. Like ciguatoxins in the Pacific Ocean (P-CTX), C-CTX-1 possesses a flexible nine-membered ring which may be a conserved feature among ciguatoxins. However, C-CTX-1 has a longer contiguous carbon backbone (57 vs 55 carbons for P-CTX-1), one extra ring, and a hemiketal in ring N but no spiroketal as found in P-CTX. C-CTX-1 possesses a primary hydroxyl which may allow selective derivatization. A minor analogue, C-CTX-2, was also isolated from fish and assigned the structure 56 epi-C-CTX-1 (2). since it slowly rearranged to C-CTX-1 in solution. Given the structural similarities between Caribbean and Pacific ciguatoxins, we propose that C-CTX-1 and C-CTX-2 arise from a Caribbean strain of the benthic dinoflagellate, Gambierdiscus toxicus.

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Ciguatera is a widespread ichthyosarcotoxaemia with dramatic and clinically important neurological features. This severe form of fish poisoning may present with either acute or chronic intoxication syndromes and constitutes a global health problem. Ciguatera poisoning is little known in temperate countries as a potentially global problem associated with human ingestion of large carnivorous fish that harbour the bioaccumulated ciguatoxins of the photosynthetic dinoflagellate Gambierdiscus toxicus. This neurotoxin is stored in the viscera of fish that have eaten the dinoflagellate and concentrated it upwards throughout the food chain towards progressively larger species, including humans. Ciguatoxin accumulates in all fish tissues, especially the liver and viscera, of at risk species. Both Pacific (P-CTX-1) and Caribbean (C-CTX-1) ciguatoxins are heat stable polyether toxins and pose a health risk at concentrations above 0.1 ppb. The presenting signs of ciguatera are primarily neurotoxic in more than 80% of cases. Such include the pathognomonic features of postingestion paraesthesiae, dysaesthesiae, and heightened nociperception. Other sensory abnormalities include the subjective features of metallic taste, pruritis, arthralgia, myalgia, and dental pain. Cerebellar dysfunction, sometimes diphasic, and weakness due to both neuropathy and polymyositis may be encountered. Autonomic dysfunction leads to hypotension, bradycardia, and hypersalivation in severe cases. Ciguatoxins are potent, lipophilic sodium channel activator toxins which bind to the voltage sensitive (site 5) sodium channel on the cell membranes of all excitable tissues. Treatment depends on early diagnosis and the early administration of intravenous mannitol. The early identification of the neurological features in sentinel patients has the potential to reduce the number of secondary cases in cluster outbreaks.

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Ciguatera is a global disease caused by the consumption of certain warm-water fish (ciguateric fish) that have accumulated orally effective levels of sodium channel activator toxins (ciguatoxins) through the marine food chain. Symptoms of ciguatera include a range of gastrointestinal, neurological and cardiovascular disturbances. This review examines progress in our understanding of ciguatera from the work of Banner in the late 1950s to the present. Similarities and differences in ciguatera in the Pacific Ocean, Indian Ocean and Caribbean Sea are highlighted, and future research directions are suggested. (C) 2000 Elsevier Science Ltd. All rights reserved.

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We report the isolation and initial characterisation of Indian Ocean ciguatoxin (I-CTX) present in toxic lipid soluble extracts isolated from ciguateric fishes collected off the Republic of Mauritius in the Indian Ocean. Following i.p. injection of this extract, mice displayed symptoms that were similar, though not identical, to those produced by Pacific and Caribbean ciguatoxins (P-CTXs and C-CTXs). Using a radiolabelled brevetoxin (PbTx) binding assay and mouse bioassay guided fractionation, I-CTX was purified by Florisil, Sephadex LH-20 and TSK HW-40S chromatography with good recovery. Isolation to purity was not possible by preparative reversed phase high-performance liquid chromatography (HPLC) due to significant losses of toxicity. However, analytical reversed phase HPLC coupled to an electrospray mass spectrometry detector identified a [M + H](+) ion at m/z 1141.58 which co-eluted with activity that displaced [3 H]-PbTx binding to rat brain. This mass corresponded to C-CTX-1, but the fragmentation pattern of I-CTX showed a different ratio of pseudo molecular and product ions. I-CTX was found to elute later than P-CTX-1 but was practically indistinguishable from C-CTX-1 on reversed phase HPLC, while the TSK HW-40S column chromatography differentiated I-CTX from the later eluting C-CTX-1. Taken together, these results indicate that I-CTX is a new ciguatoxin (CTX) responsible for ciguatera caused by reef fish in the Indian Ocean. (C) 2002 Elsevier Science Ltd. All rights reserved.

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Ciguatoxins are cyclic polyether toxins, derived from marine dinoflagellates, which are responsible for the symptoms of ciguatera poisoning. Ingestion of tropical and subtropical fin fish contaminated by ciguatoxins results in an illness characterised by neurological, cardiovascular and gastrointestinal disorders. The pharmacology of ciguatoxins is characterised by their ability to cause persistent activation of voltage-gated sodium channels, to increase neuronal excitability and neurotransmitter release, to impair synaptic vesicle recycling, and to cause cell swelling. It is these effects, in combination with an action to block voltage-gated potassium channels at high doses, which are believed to underlie the complex of symptoms associated with ciguatera. This review examines the sources, structures and pharmacology of ciguatoxins. In particular, attention is placed on their cellular modes of actions to modulate voltage-gated ion channels and other Na+-dependent mechanisms in numerous cell types and to current approaches for detection and treatment of ciguatera.

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Ciguatera is a global disease caused by the consumption of certain warm-water fish that have accumulated orally effective levels of sodium channel activator toxins (ciguatoxins) through the marine food chain. Symptoms of ciguatera arising from the consumption of ciguateric fish include a range of gastrointestinal, neurological and cardiovascular disturbances. This review examines progress in our understanding of ciguatera from an Australian perspective, especially the laboratory-based research into the problem that was initiated by the late "Bob" Endean at the University of Queensland.

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Optimised gradient reversed-phase high-performance liquid chromatography electrospray ionisation mass spectrometry (LC/MS) methods, in combination with a [H-3]-brevetoxin binding assay (RLB), revealed multiple ciguatoxins in a partially purified extract of a highly toxic Lutjanus sebae (red emperor) from the Indian Ocean. Two major ciguatoxins of 1140.6 Da (I-CTX-1 and -2) and two minor ciguatoxins of 1156.6 Da (I-CTX-3 and -4) were identified. Accurate mass analysis revealed that I-CTX-1 and -2 and Caribbean C-CTX-1 had indistinguishable masses (1140.6316 Da, at 0.44 ppm resolution). Toxicity estimated from LC/MS/RLB responses indicated that I-CTX-1 and -2 were both similar to 60% the potency of Pacific ciguatoxin-1 (P-CTX-1). In contrast to ciguatoxins of the Pacific where the more oxidised ciguatoxins are more potent, I-CTX-3 and -4 were similar to 20% of P-CTX-1 potency. Interconversion in dilute acid or on storage, typical of spiroketal and hemiketal functionality found in P-CTXs and C-CTXs, respectively, was not observed to occur between I-CTX-1 and -2. The ratio of CTX-1 and -2 varied depending on the fish extract being analysed. These results suggest that I-CTX-1 and -2 may arise from separate dinoflagellate precursors that may be oxidatively biotransformed to I-CTX-3 and -4 in fish. (C) 2002 Published by Elsevier Science Ltd.

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The basis for the neuroprotectant effect of D-mannitol in reducing the sensory neurological disturbances seen in ciguatera poisoning, is unclear. Pacific ciguatoxin-1 (P-CTX-1), at a concentration 10 nM, caused a statistically significant swelling of rat sensory dorsal root ganglia (DRG) neurons that was reversed by hyperosmolar 50 MM D-mannitol. However, using electron paramagnetic resonance (EPR) spectroscopy, it was found that P-CTX-1 failed to generate hydroxyl free radicals at concentrations of toxin that caused profound effects on neuronal excitability. Whole-cell patch-clamp recordings from DRG neurons revealed that both hyper- and iso-osmolar 50 MM D-mannitol prevented the membrane depolarisation and repetitive firing of action potentials induced by P-CTX-1. In addition, both hyper- and iso-osmolar 50 MM D-mannitol prevented the hyperpolarising shift in steady-state inactivation and the rise in leakage current through tetrodotoxin (TTX)-sensitive Na-v channels, as well as the increased rate of recovery from inactivation of TTX-resistant Nav channels induced by P-CTX-1. D-Mannitol also reduced, but did not prevent, the inhibition of peak TTX-sensitive and TTX-resistant I-Na amplitude by P-CTX-1. Additional experiments using hyper- and isoosmolar D-sorbitol, hyperosmolar sucrose and the free radical scavenging agents Trolox (R) and L-ascorbic acid showed that these agents, unlike D-mannitol, failed to prevent the effects of P-CTX-1 on spike electrogenesis and Na-v channel gating. These selective actions of D-mannitol indicate that it does not act purely as an osmotic agent to reduce swelling of nerves, but involves a more complex action dependent on the Nav channel subtype, possibly to alter or reduce toxin association. (c) 2005 Elsevier Ltd. All rights reserved.

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Light-microscopic and electron-microscopic studies of the tropical marine sponge Haliclona sp. (Or der: Haplosclerida Family: Haliclonidae) from Heron Island, Great Barrier Reef, have revealed that this sponge is characterized by the presence of dinoflagellates and by nematocysts. The dinoflagellates are 7-10 mu m in size, intracellular, and contain a pyrenoid with a single stalk, whereas the single chloroplast is branched, curved, and lacks grana. Mitochondria are present, and the nucleus is oval and has distinct chromosomal structure. The dinoflagellates are morphologically similar to Symbiodinium microadriaticum, the common intracellular symbiont of corals, although more detailed biochemical and molecular studies are required to provide a precise taxonomic assignment. The major sponge cell types found in Haliclona sp, are spongocytes, choanocytes, and archaeocytes; groups of dinoflagellates are enclosed within large vacuoles in the archaeocytes. The occurrence of dinoflagellates in marine sponges has previously been thought to be restricted to a small group of sponges including the excavating hadromerid sponges; the dinoflagellates in these sponges are usually referred to as symbionts. The role of the dinoflagellates present in Haliclona sp. as a genuine symbiotic partner requires experimental investigation. The sponge grows on coral substrates, from which it may acquire the nematocysts, and shows features, such as mucus production, which are typical of some excavating sponges. The cytotoxic alkaloids, haliclonacyclamines A and B, associated with Haliclona sp. are shown by Percoll density gradient fractionation to be localized within the sponge cells rather than the dinoflagellates. The ability to synthesize bioactive compounds such as the haliclonacyclamines may help Haliclona sp. to preserve its remarkable ecological niche.

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Dinoflagellates exist in symbiosis with a number of marine invertebrates including giant clams, which are the largest of these symbiotic organisms. The dinoflagellates (Symbiodinium sp.) live intercellularly within tubules in the mantle of the host clam. The transport of inorganic carbon (Ci) from seawater to Symbiodinium (=zooxanthellae) is an essential function of hosts that derive the majority of their respiratory energy from the photosynthate exported by the zooxanthellae. Immunolocalisation studies show that the host has adapted its physiology to acquire, rather than remove CO2, from the haemolymph and clam tissues. Two carbonic anhydrase (CA) isoforms (32 and 70 kDa) play an essential part in this process. These have been localised to the mantle and gill tissues where they catalyse the interconversion of HCO3- to CO2, which then diffuses into the host tissues. The zooxanthellae exhibit a number of strategies to maximise Ci acquisition and utilisation. This is necessary as they express a form II Rubisco that has poor discrimination between CO2 and O-2. Evidence is presented for a carbon concentrating mechanism (CCM) to overcome. this disadvantage. The CCM incorporates the presence of a light-activated CA activity, a capacity to take up both HCO3- and CO2, an ability to accumulate an elevated concentration of Ci within the algal cell, and localisation of Rubisco to the pyrenoid. These algae also express both external and intracellular CAs, with the intracellular isoforms being localised to the thylakoid lumen and pyrenoid. These results have been incorporated into a model that explains the transport of Ci from seawater through the clam to the zooxanthellae.

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Four new species of dinoflagellate cysts are described from Callovian to lower Oxfordian (Jurassic) sediments of the Timor Sea, northwestern Australia. These comprise Evansia? lacryma, Egmontodinium elongatum, Leptodinium? ancoralium, and Nannoceratopsis reticulata. They are rare to common constituents of the Rigaudella aemula dinoflagellate cyst Interval Zone, and may prove useful for regional biostratigraphic correlation. (c) 2005 Elsevier B.V. All rights reserved.

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The aeolid nudibranch Pteraeolidia ianthina hosts symbiotic dinoflagellates in the same way as many reef-building corals. This widespread Indo-Pacific sea slug ranges from tropical to temperate waters, and offers a unique opportunity to examine a symbiosis that occurs over a large latitudinal gradient. We used partial 28S and 18S nuclear ribosomal (nr) DNA to examine the genetic diversity of the Symbiodinium dinoflagellates contained within F ianthina. We detected Symbiodinium from genetic clades A, B, C and D. P. ianthina from tropical regions (Singapore, Sulawesi) host Symbiodinium clade C or D or both; those from the subtropical eastern Australian coast (Heron Island, Mon Repo, Moreton Bay, Tweed Heads) host Symbiodinium clade C, but those from the temperate southeastern Australian coastline (Port Stephens, Bare Island) host clade A or B or both. The Symbiodinium populations within 1 individual nudibranch could be homogeneous or heterogeneous at inter- or intra-clade levels (or both). Our results suggested that the Pteraeolidia-Symbiodinium symbiosis is flexible and favours symbiont phylotypes best adapted for that environment. This flexibility probably reflects the function of the symbiont clade in relation to the changing environments experienced along the latitudinal range, and facilitates the large geographic range of P. ianthina.

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Background: Cnidarian - dinoflagellate intracellular symbioses are one of the most important mutualisms in the marine environment. They form the trophic and structural foundation of coral reef ecosystems, and have played a key role in the evolutionary radiation and biodiversity of cnidarian species. Despite the prevalence of these symbioses, we still know very little about the molecular modulators that initiate, regulate, and maintain the interaction between these two different biological entities. In this study, we conducted a comparative host anemone transcriptome analysis using a cDNA microarray platform to identify genes involved in cnidarian - algal symbiosis. Results: We detected statistically significant differences in host gene expression profiles between sea anemones ( Anthopleura elegantissima) in a symbiotic and non-symbiotic state. The group of genes, whose expression is altered, is diverse, suggesting that the molecular regulation of the symbiosis is governed by changes in multiple cellular processes. In the context of cnidarian dinoflagellate symbioses, we discuss pivotal host gene expression changes involved in lipid metabolism, cell adhesion, cell proliferation, apoptosis, and oxidative stress. Conclusion: Our data do not support the existence of symbiosis- specific genes involved in controlling and regulating the symbiosis. Instead, it appears that the symbiosis is maintained by altering expression of existing genes involved in vital cellular processes. Specifically, the finding of key genes involved in cell cycle progression and apoptosis have led us to hypothesize that a suppression of apoptosis, together with a deregulation of the host cell cycle, create a platform that might be necessary for symbiont and/or symbiont-containing host cell survival. This first comprehensive molecular examination of the cnidarian - dinoflagellate associations provides critical insights into the maintenance and regulation of the symbiosis.

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This report details a reliable and efficient RNA extraction protocol for the symbiotic dinoflagellate Symbiodinium microadriaticum Freudenthal (Gymnodiniales, Dinophyceae). The method typically gives yields of 500 mu g total RNA from 0.4 g wet weight of algae, and, in comparison to current protocols, it is technically simple and less time consuming. This method isolates high-quality, intact RNA from in vine cultured as well as host-isolated cells, as demonstrated by spectrophotometry, gel electrophoresis, and northern analysis. The total RNA obtained was suitable for reverse transcription and PCR amplification of Symbiodinium cDNAs. We have successfully applied our method to isolate total RNA from a different dinoflagellate, Amphidinium carterae Hulburt (Gymnodiniales, Dinophyceae), found in symbiotic association with marine invertebrates.

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The early effects of heat stress on the photosynthesis of symbiotic dinoflagellates (zooxanthellae) within the tissues of a reef-building coral were examined using pulse-amplitude-modulated (PAM) chlorophyll fluorescence and photorespirometry. Exposure of Stylophora pistillata to 33 and 34 degrees C for 4 h resulted in (1) the development of strong non-photochemical quenching (qN) of the chlorophyll fluorescence signal, (2) marked decreases in photosynthetic oxygen evolution, and (3) decreases in optimal quantum yield (F-v/F-m) of photosystern II (PSII), Quantum yield decreased to a greater extent on the illuminated surfaces of coral branches than on lower (shaded) surfaces, and also when high irradiance intensities were combined with elevated temperature (33 degrees C as opposed to 28 degrees C), qN collapsed in heat-stressed samples when quenching analysis was conducted in the absence of oxygen, Collectively, these observations are interpreted as the initiation of photoprotective dissipation of excess absorbed energy as heat (qN) and O-2-dependent electron flow through the Mehler-Ascorbate-Peroxidase cycle (MAP-cycle) following the point at which the rate of light-driven electron transport exceeds the capacity of the Calvin cycle. A model for coral bleaching is proposed whereby the primary site of heat damage in S, pistillata is carboxylation within the Calvin cycle, as has been observed during heat damage in higher plants, Damage to PSII and a reduction in F-v/F-m (i.e. photoinhibition) are secondary effects following the overwhelming of photoprotective mechanisms by light. This secondary factor increases the effect of the primary variable, temperature. Potential restrictions of electron flow in heat-stressed zooxanthellae are discussed with respect to Calvin cycle enzymes and the unusual status of the dinoflagellate Rubisco, Significant features of our model are that (1) damage to PSII is not the initial step in the sequence of heat stress in zooxanthellae, acid (2) light plays a key secondary role in the initiation of the bleaching phenomena.