The Mechanism of Diarrhetic Shellfish Poisoning Toxin Production in Prorocentrum spp.: Physiological and Molecular Perspectives

Molecular Phylogeny, Morphology, Growth and Toxicity of Three Benthic Dinoflagellates Ostreopsis sp. 9, Prorocentrum lima and Coolia monotis Developing in Strait of Gibraltar, Southwestern Mediterranean

Few works have been carried out on benthic harmful algal blooms (BHAB) species in the southern Mediterranean and no data are available for the highly dynamic Strait of Gibraltar (western Mediterranean waters). For the first time, Ostreopsis sp. 9, Prorocentrum lima and Coolia monotis were isolated in this key region in terms of exchanges between the Atlantic Ocean and the Mediterranean and subject to intense maritime traffic. Ribotyping confirmed the morphological identification of these three dinoflagellates species. Monoclonal cultures were established and the maximum growth rate and cell yield were measured at a temperature of 24 °C and an irradiance of 90 µmol photons m-2 s-1, for each species: 0.26 ± 0.02 d-1 (8.75 × 103 cell mL-1 after 28 days) for Ostreopsis sp. 9, 0.21 ± 0.01 d-1 (49 × 103 cell mL-1 after 145 days) for P. lima and 0.21 ± 0.01 d-1 (10.02 × 103 cell mL-1 after 28 days) for C. monotis. Only P. lima was toxic with concentrations of okadaic acid and dinophysistoxin-1 measured in optimal growth conditions ranging from 6.4 pg cell-1 to 26.97 pg cell-1 and from 5.19 to 25.27 pg cell-1, respectively. The toxin content of this species varied in function of the growth phase. Temperature influenced the growth and toxin content of P. lima. Results suggest that future warming of Mediterranean coastal waters may lead to higher growth rates and to increases in cellular toxin levels in P. lima. Nitrate and ammonia affected the toxin content of P. lima but no clear trend was noted. In further studies, we have to isolate other BHAB species and strains from Strait of Gibraltar waters to obtain more insight into their diversity and toxicity.

Occurrence and risk assessment of okadaic acid, dinophysistoxin-1, dinophysistoxin-2, and dinophysistoxin-3 in seafood from South Korea

The okadaic acid (OA)-group toxins, including OA, dinophysistoxin-1 (DTX1), dinophysistoxin-2 (DTX2), and dinophysistoxin-3 (DTX3), cause diarrheic shellfish poisoning in humans. To manage OA-group toxins more strictly, Korean regulations were recently revised to consider OA, DTX1, DTX2, and DTX3 combined. Thus, our study characterized the occurrence of OA, DTX1, DTX2, and DTX3 in seafood distributed across South Korea, and a risk assessment of seafood consumption was conducted. Two hundred and seventeen samples from 16 bivalve and 7 non-bivalve species collected from three representative coastal areas in 2021 were analyzed via liquid chromatography-tandem mass spectrometry. OA, DTX1, and DTX3 were detected in 2.3%, 4.1%, and 9.2% of the examined samples, with positive mean levels of 11.3, 16.4, and 40.9 µg/kg, respectively. DTX2 was not detected in any of the samples. At least one OA-group toxin was detected in the bivalve samples, including blood clams, pan shells, hard clams, mussels, and scallops, whereas none were detected in non-bivalves. The estimated acute exposure to OA-group toxins through the intake of seafood in the Korean population and consumer groups was low, ranging from 24.7 to 74.5% of the recommended acute reference dose (ARfD) of 0.33 μg OA equivalents/kg body weight. However, for the scallop consumers aged 7-12 years, acute exposure to OA-group toxins exceeded the ARfD, indicating a possible health risk. These results suggest that including DTX3 in the new regulatory limits is appropriate to protect Korean seafood consumers from exposure to OA-group toxins.

Oriented-aptamer encoded magnetic nanosensor with laser-induced fluorescence for ultrasensitive test of okadaic acid

Okadaic acid (OA) biotoxin acts a well-established inhibitor of protein phosphatase even a tumor promoter of human being, arouse great attention in safety monitoring. However, the powerful and convenient nanosensing technologies for addressing the demands such as rapidity, high sensitivity, and stability in the in-field test of OA shellfish toxin is still scarce. Herein, a high-performance magnetic biometric nanosensor (MBNS) integrating oriented aptamers and ultrasensitive laser-induced fluorescence (LIF) was firstly proposed for the in-field detection of trace OA in seafoods. High-density aptamers hybridized with FAM-labeled cDNA were tethered to the surface of AuNPs on magnetic MIL-101@Fe3O4, and then finely regulated by mercaptohexyl alcohol (MCH) to be orderly assembled, as was successfully utilized to engineer an active biological nanosensor for highly specific recognition of OA. Aptamers anchored on magnetic Fe3O4@MOF@AuNPs activate a biometric microreactor of OA, in which the superior LIF properties, conformation regulation of aptamer, and the specific recognition using aptamer genes were adopted. The magnetic nanosensor with an excellent specificity and super sensitivity for OA analysis was achieved within 20 min. Moreover, the content of captured OA could facilely be recorded by measuring the fluorescence intensity, and the limit of detection (LOD) and limit of quantitation of OA (LOQ) reached 0.015 and 0.050 ng/mL respectively, which was far better than most aptamer-based biometric sensing methods. The feasibility for accurate test of trace OA toxin in the fortified shellfish samples was validated with the recovery yields of 88.2-107.5% and RSD of 0.5-7.6%, respectively. The result demonstrated that the oriented-aptamer encoded MNS had significant practical values in rapid and ultrasensitive detection of OA biotoxin and the related safety applications.

Diversity and distribution of benthic dinoflagellates in Tonga include the potentially harmful genera Gambierdiscus and Fukuyoa

Benthic dinoflagellates that can cause illness, such as ciguatera poisoning (CP), are prevalent around the Pacific but are poorly described in many locations. This study represents the first ecological assessment of benthic harmful algae species in the Kingdom of Tonga, a country where CP occurs regularly. Surveys were conducted in June 2016 in the Tongatapu island group, and in June 2017 across three island groups: Ha'apai, Vava'u, and Tongatapu. Shallow subtidal coastal habitats were investigated by measuring water quality parameters and conducting quadrat surveys. Microalgae samples were collected using either macrophyte collection or the artificial substrate method. Benthic dinoflagellates (Gambierdiscus and/or Fukuyoa, Ostreopsis, and Prorocentrum) were counted using light microscopy, followed by molecular analyses (real-time PCR in 2016 and high throughput sequencing (metabarcoding) in 2017) to identify Gambierdiscus and Fukuyoa to species level. Six species were detected from the Tongatapu island group in 2016 (G. australes, G. carpenteri, G. honu, G. pacificus, F. paulensis, and F. ruetzleri) using real-time PCR. Using the metabarcoding approach in 2017, a total of eight species (G. australes, G. carpenteri, G. honu, G. pacificus, G. cheloniae, G. lewisii, G. polynesiensis, and F. yasumotoi) were detected. Species were detected in mixed assemblages of up to six species, with G. pacificus and G. carpenteri being the most frequently observed. Ha'apai had the highest diversity with eight species detected, which identifies this area as a Gambierdiscus diversity 'hotspot'. Vava'u and Tongatapu had three and six species found respectively. Gambierdiscus polynesiensis, a described ciguatoxin producer and proposed causative agent of CP was found only in Ha'apai and Vava'u in 2017, but not in Tongatapu in either year. Ostreopsis spp. and Prorocentrum spp. were also frequently observed, with Prorocentrum most abundant at the majority of sites. In 2016, the highest number of Gambierdiscus and/or Fukuyoa cells were observed on seagrass (Halodule uninervis) from Sopu, Tongatapu. In 2017, the highest numbers of Gambierdiscus and/or Fukuyoa from artificial substrate samples were recorded in the Halimeda dominant habitat at Neiafu Tahi, Vava'u, a low energy site. This raised the question of the effect of wave motion or currents on abundance measurements from artificial substrates. Differences in detection were noticed between macrophytes and artificial substrates, with higher numbers of species found on artificial substrates. This study provides a baseline of benthic dinoflagellate distributions and diversity for Tonga that may be used for future studies and the development of monitoring programmes.

Analysis of research status and trends on marine benthic dinoflagellate toxins: A bibliometric study based on web of science database and VOSviewer

Marine benthic dinoflagellate toxins, potent bioactive compounds with wide-ranging presence in marine ecosystems, have surged in response to global climate change and human activities, prompting an urgent and imperative inquiry. This study conducts an in-depth review of contemporary research concerning these toxins, employing meticulous bibliometric analysis. Leveraging a dataset of 736 relevant literatures sourced from the Web of Science (spanning from 2000 to May 2023), our analysis delves comprehensively into the scientific discourse surrounding these toxic compounds. Employing tools such as VOSviewer, co-citation analysis, co-occurrence analysis, and cluster analysis, our study yields nuanced insights into the intricate characteristics and trajectories of the field. The co-citation analysis underscores the pivotal role played by benthic and epiphytic dinoflagellates like Ostreopsis and Gambierdiscus in shaping prevailing research trends. Our study identifies four distinct research directions, encompassing the domains of ecology, toxicology, toxin production, and taxonomy. Moreover, it traces the evolutionary journey of research stages, marking the transition from a focus on taxonomy to an emphasis on unraveling molecular mechanisms. The culmination of our comprehensive analysis yields three pertinent research recommendations: a call for widescale global studies, the advancement of rapid toxin monitoring techniques, and a deeper exploration of the factors influencing toxin synthesis and toxicity. These findings provide invaluable insights to researchers grappling with the complex realm of harmful algal blooms and substantially enrich the understanding of this pivotal and pressing field.

Modelling spatiotemporal distributions of Vulcanodinium rugosum and pinnatoxin G in French Mediterranean lagoons: Application to human health risk characterisation

Consumption of seafood contaminated by phycotoxins produced by harmful algae is a major issue in human public health. Harmful algal blooms are driven by a multitude of environmental variables; therefore predicting human dietary exposure to phycotoxins based on these variables is a promising approach in health risk management. In this study, we attempted to predict the human health risks associated with Vulcanodinium rugosum and its neurotoxins, pinnatoxins (PnTXs), which have been regularly found in Mediterranean lagoons since their identification in 2011. Based on environmental variables collected over 1 year in four Mediterranean lagoons, we developed linear mixed models to predict the presence of V. rugosum and PnTX G contamination of mussels. We found that the occurrence of V. rugosum was significantly associated with seawater temperature. PnTX G contamination of mussels was highest in summer but persisted throughout the year. This contamination was significantly associated with seawater temperature and the presence of V. rugosum with a time lag, but not with dissolved PnTX G in seawater. By using the contamination model predictions and their potential variability/uncertainty, we calculated the human acute dietary exposures throughout the year and predicted that 25% of people who consume mussels could exceed the provisional acute benchmark value during the warmest periods. We suggest specific recommendations to monitor V. rugosum and PnTX G.

Transcriptomic Analysis of the Response of the Toxic Dinoflagellate Prorocentrum lima to Phosphorous Limitation

Some dinoflagellates cause harmful algal blooms, releasing toxic secondary metabolites, to the detriment of marine ecosystems and human health. Phosphorus (P) is a limiting macronutrient for dinoflagellate growth in the ocean. Previous studies have been focused on the physiological response of dinoflagellates to ambient P changes. However, the whole-genome's molecular mechanisms are poorly understood. In this study, RNA-Seq was utilized to compare the global gene expression patterns of a marine diarrheic shellfish poisoning (DSP) toxin-producing dinoflagellate, Prorocentrum lima, grown in inorganic P-replete and P-deficient conditions. A total of 148 unigenes were significantly up-regulated, and 30 unigenes were down-regulated under 1/4 P-limited conditions, while 2708 unigenes were significantly up-regulated, and 284 unigenes were down-regulated under 1/16 P-limited conditions. KEGG enrichment analysis of the differentially expressed genes shows that genes related to ribosomal proteins, glycolysis, fatty acid biosynthesis, phagosome formation, and ubiquitin-mediated proteolysis are found to be up-regulated, while most of the genes related to photosynthesis are down-regulated. Further analysis shows that genes encoding P transporters, organic P utilization, and endocytosis are significantly up-regulated in the P-limited cells, indicating a strong ability of P. lima to utilize dissolved inorganic P as well as intracellular organic P. These transcriptomic data are further corroborated by biochemical and physiological analyses, which reveals that under P deficiency, cellular contents of starch, lipid, and toxin increase, while photosynthetic efficiency declines. Our results indicate that has P. lima evolved diverse strategies to acclimatize to low P environments. The accumulation of carbon sources and DSP toxins could provide protection for P. lima to cope with adverse environmental conditions.

Adaptive responses of geographically distinct strains of the benthic dinoflagellate, Prorocentrum lima (Dinophyceae), to varying light intensity and photoperiod

The toxic Prorocentrum lima complex can potentially cause serious harm to the benthos and entire food chain. Studies have revealed physiological differences in strains from different regions related to local environment, while differences in the adaptive responses of P. lima complex should be urgently assessed. Hence, this study explored the adaptive responses to varying light intensities and photoperiods of two P. lima complex strains SHG101 and 3XS34, isolated from the Bohai Sea and the South China Sea, respectively. We found the highest cell density of 7.49 × 104 cells mL-1 recorded in the 3XS strain in the stationary phase with high light intensity exposure. No significant difference was observed in growth rate among SHG groups, however, significant differences were found among 3XS groups ranging from 0.176 to 0.311 d-1. Three key pigments Chl a, Peri, and Fuco accounted for up to 60% of the total pigments. Production and concentrations of pigments and Fv/Fm values exhibit a significant negative correlation with high light intensity and growth. Conversely, total diarrhetic shellfish toxin content and the proportion of diol esters increased to varying degrees after high intensity light exposure, with 3XS strain under high light intensity and a photoperiod of light and darkness (12L:12D) consistently exhibiting the highest levels, finally reaching a maximum (21.6 pg cell-1) at day 28. A shortened photoperiod of high light intensity (8L:16D) resulted in impaired recovery compared with 12L:12D. Furthermore, 3XS showed more delayed and intense adaptive responses, indicating a stronger tolerance compared to SHG. Collectively, these results directly characterized variation in the adaptive responses of geographically distinct strains of P. lima complex, highlighting the previously ignored potential risk diversity of this species.

Benthic harmful microalgae and their impacts in South America

Public awareness about Benthic Harmful Algal Blooms (BHABs) and their negative impacts has increased substantially over the past few decades. Even so, reports of BHABs remain relatively scarce in South America (SA). This paper provides a comprehensive overview of the current state of knowledge on BHABs in the continent, by integrating data from published articles, books, and technical reports. We recorded ∼300 different occurrences of potentially toxic BHAB species over the Caribbean, Atlantic and Pacific coasts, mostly in marine (>95%) but also in estuarine areas located from 12⁰36' N to 54⁰53' S. Over 70% of the data was published/released within the past 10 years, and ∼85% were concentrated in Brazil, Venezuela, Ecuador and Colombia. Benthic species were mainly associated with macroalgae, seagrass and sediment. Incidental detection in the plankton was also relevant, mainly in places where studies targeting BHAB species are still rare, like Argentina, Uruguay, Chile and Peru. The study listed 31 infrageneric taxa of potentially toxic benthic dinoflagellates and eight of estuarine cyanobacteria occurring in SA, with the greatest species diversity recorded in the equatorial-tropical zone, mainly in northeastern Brazil (Atlantic), Venezuela and Colombia (Caribbean), and the Galapagos Islands, Ecuador (Pacific). Local strains of Amphidinium, Gambierdiscus, Coolia and Prorocentrum spp. produced toxic compounds of emerging concern. Prorocentrum lima species complex was the most common and widely distributed taxon, followed by Ostreopsis cf. ovata. In fact, these two dinoflagellates were associated with most BHAB events in SA. Whereas the former has caused the contamination of multiple marine organisms and cases of Diarrhetic Shellfish Poisoning in subtropical and temperate areas, the latter has been associated with faunal mortalities and is suspected of causing respiratory illness to beach users in tropical places. Ciguatera Poisoning has been reported in Colombia (∼240 cases; no deaths) and Venezuela (60 cases; two deaths), and may be also a risk in other places where Gambierdiscus spp. and Fukuyoa paulensis have been reported, such as the Galapagos Islands and the tropical Brazilian coast. Despite the recent advances, negative impacts from BHABs in SA are intensified by limited research/training funding, as well as the lack of official HAB monitoring and poor analytical capability for species identification and toxin detection in parts of the continent.

Variation profile of diarrhetic shellfish toxins and diol esters derivatives of Prorocentrum lima during growth by high-resolution mass spectrometry

Prorocentrum lima is a widely distributed toxigenic benthic dinoflagellate whose production of diarrhetic shellfish toxins threatens the shellfish industry and seafood safety. Current research primarily assesses the difference between free and post-hydrolysis total toxin methods, ignoring the impact of different detection methods on technical accuracy. After removing matrix interference with SPE extraction, a thorough HRMS strategy was created in this study. Alkaline hydrolysis could release the diol esters and played a crucial role in obtaining an accurate assessment of toxin levels, achieving satisfactory recoveries (74.0-147.0%) and repeatability (relative deviation <12.3%). The HRMS approach evaluated toxin profile variation during the growth of three P. lima strains from China. A total of 24 toxin contents varying in composition, content, and a high proportion were detected. The SHG, HN, and 3XS strains had total toxin contents of 23.3 ± 1.74, 19.8 ± 1.25, and 19.5 ± 1.58 pg cell^-1, respectively. The diol esters proportion varied among the strains, with SHG having 58.9-69.9, HN having 75.4-86.5, and 3XS having 91.0-91.7%. The variety of toxins produced by distinct P. lima strains highlighted the significance of this method for appropriately measuring the risks connected with DSTs manufacturing. The proposed approach provides a technical basis for gathering comprehensive and accurate data on the potential risks of P. lima DSTs production, with significant implications for ensuring food safety and preventing harmful toxins from spreading in the marine ecosystem.

Effects of lipophilic phycotoxin okadaic acid on the early development and transcriptional expression of marine medaka Oryzias melastigma

The lipophilic okadaic acid (OA)-group toxins produced by some species of Dinophysis spp. and Prorocentrum spp. marine dinoflagellates have been frequently and widely detected in natural seawater environments, e.g. 2.1∼1780 ng/L in Spanish sea and 5.63∼27.29 ng/L in the Yellow Sea of China. The toxicological effects of these toxins dissolved in seawater on marine fish is still unclear. Effects of OA on the embryonic development and 1-month old larvae of marine medaka (Oryzias melastigma) were explored and discussed in this study. Significantly increased mortality and decreased hatching rates occurred for the medaka embryos exposed to OA at 1.0 μg/mL. Diverse malformations including spinal curvature, dysplasia and tail curvature were also observed in the embryos exposed to OA and the heart rates significantly increased at 11 d post fertilization. The 96 h LC₅₀ of OA for 1-month old larvae was calculated at 3.80 μg/mL. The reactive oxygen species (ROS) was significantly accumulated in medaka larvae. Catalase (CAT) enzyme activity was significantly increased in 1-month old larvae. Acetylcholinesterase (AChE) activity significantly increased with a dose-dependent pattern in 1-month old larvae. Differentially expressed genes (DEGs) were enriched in 11 KEGG pathways with Q value < 0.05 in 1-month old medaka larvae exposed to OA at 0.38 μg/mL for 96 h, which were mainly related to cell division and proliferation, and nervous system. Most of DEGs involved in DNA replication, cell cycle, nucleotide excision repair, oocyte meiosis, and mismatch repair pathways were significantly up-regulated, while most of DEGs involved in synaptic vesicle cycle, glutamatergic synapse, and long-term potentiation pathways were markedly down-regulated. This transcriptome analysis demonstrated that a risk of cancer developing was possibly caused by OA due to DNA damage in marine medaka larvae. In addition, the neurotoxicity of OA was also testified for marine fish, which potentially cause major depressive disorder (MDD) via the up-regulated expression of NOS1 gene. The genotoxicity and neurotoxicity of OA to marine fish should be paid attention to and explored further in the future.

Acute Toxicity of the Dinoflagellate Amphidinium carterae on Early Life Stages of Zebrafish (Danio rerio)

Dinoflagellates of the genus Amphidinium can produce a variety of polyketides, such as amphidinols (AMs), amphidinoketides, and amphidinin, that have hemolytic, cytotoxic, and fish mortality properties. AMs pose a significant threat to ecological function due to their membrane-disrupting and permeabilizing properties, as well as their hydrophobicity. Our research aims to investigate the disparate distribution of AMs between intracellular and extracellular environments, as well as the threat that AMs pose to aquatic organisms. As a result, AMs containing sulphate groups such as AM19 with lower bioactivity comprised the majority of A. carterae strain GY-H35, while AMs without sulphate groups such as AM18 with higher bioactivity displayed a higher proportion and hemolytic activity in the extracellular environment, suggesting that AMs may serve as allelochemicals. When the concentration of extracellular crude extracts of AMs reached 0.81 µg/mL in the solution, significant differences in zebrafish embryonic mortality and malformation were observed. Over 96 hpf, 0.25 μL/mL of AMs could cause significant pericardial edema, heart rate decrease, pectoral fin deformation, and spinal deformation in zebrafish larvae. Our findings emphasized the necessity of conducting systematic research on the differences between the intracellular and extracellular distribution of toxins to gain a more accurate understanding of their effects on humans and the environment.

Transcriptomic analysis of polyketide synthesis in dinoflagellate, Prorocentrum lima

The benthic dinoflagellate Prorocentrum lima is among the most common toxic morphospecies with a cosmopolitan distribution. P. lima can produce polyketide compounds, such as okadaic acid (OA), dinophysistoxin (DTX) and their analogues, which are responsible for diarrhetic shellfish poisoning (DSP). Studying the molecular mechanism of DSP toxin biosynthesis is crucial for understanding the environmental driver influencing toxin biosynthesis as well as for better monitoring of marine ecosystems. Commonly, polyketides are produced by polyketide synthases (PKS). However, no gene has been confirmatively assigned to DSP toxin production. Here, we assembled a transcriptome from 94,730,858 Illumina RNAseq reads using Trinity, resulting in 147,527 unigenes with average sequence length of 1035 nt. Using bioinformatics analysis methods, we found 210 unigenes encoding single-domain PKS with sequence similarity to type I PKSs, as reported in other dinoflagellates. In addition, 15 transcripts encoding multi-domain PKS (forming typical type I PKSs modules) and 5 transcripts encoding hybrid nonribosomal peptide synthetase (NRPS)/PKS were found. Using comparative transcriptome and differential expression analysis, a total of 16 PKS genes were identified to be up-regulated in phosphorus-limited cultures, which was related to the up regulation of toxin expression. In concert with other recent transcriptome analyses, this study contributes to the building consensus that dinoflagellates may utilize a combination of Type I multi-domain and single-domain PKS proteins, in an as yet undefined manner, to synthesize polyketides. Our study provides valuable genomic resource for future research in order to understand the complex mechanism of toxin production in this dinoflagellate.

Deciphering interactions between the marine dinoflagellate Prorocentrum lima and the fungus Aspergillus pseudoglaucus

The comprehension of microbial interactions is one of the key challenges in marine microbial ecology. This study focused on exploring chemical interactions between the toxic dinoflagellate Prorocentrum lima and a filamentous fungal species, Aspergillus pseudoglaucus, which has been isolated from the microalgal culture. Such interspecies interactions are expected to occur even though they were rarely studied. Here, a co-culture system was designed in a dedicated microscale marine-like condition. This system allowed to explore microalgal-fungal physical and metabolic interactions in presence and absence of the bacterial consortium. Microscopic observation showed an unusual physical contact between the fungal mycelium and dinoflagellate cells. To delineate specialized metabolome alterations during microalgal-fungal co-culture metabolomes were monitored by high-performance liquid chromatography coupled to high-resolution mass spectrometry. In-depth multivariate statistical analysis using dedicated approaches highlighted (1) the metabolic alterations associated with microalgal-fungal co-culture, and (2) the impact of associated bacteria in microalgal metabolome response to fungal interaction. Unfortunately, only a very low number of highlighted features were fully characterized. However, an up-regulation of the dinoflagellate toxins okadaic acid and dinophysistoxin 1 was observed during co-culture in supernatants. Such results highlight the importance to consider microalgal-fungal interactions in the study of parameters regulating toxin production.

Upregulation of Peridinin-Chlorophyll A-Binding Protein in a Toxic Strain of Prorocentrum hoffmannianum under Normal and Phosphate-Depleted Conditions

Some strains of the dinoflagellate species Prorocentrum hoffmannianum show contrasting ability to produce diarrhetic shellfish poisoning (DSP) toxins. We previously compared the okadaic acid (OA) production level between a highly toxic strain (CCMP2804) and a non-toxic strain (CCMP683) of P. hoffmannianum and revealed that the cellular concentration of OA in CCMP2804 would increase significantly under the depletion of phosphate. To understand the molecular mechanisms, here, we compared and analyzed the proteome changes of both strains growing under normal condition and at phosphate depletion using two-dimensional gel electrophoresis (2-DE). There were 41 and 33 differential protein spots observed under normal condition and phosphate depletion, respectively, of which most were upregulated in CCMP2804 and 22 were common to both conditions. Due to the lack of matched peptide mass fingerprints in the database, de novo peptide sequencing was applied to identify the differentially expressed proteins. Of those upregulated spots in CCMP2804, nearly 60% were identified as peridinin-chlorophyll a-binding protein (PCP), an important light-harvesting protein for photosynthesis in dinoflagellates. We postulated that the high expression of PCP encourages the production of DSP toxins by enhancing the yields of raw materials such as acetate, glycolate and glycine. Other possible mechanisms of toxicity related to PCP might be through triggering the transcription of non-ribosomal peptide synthetase/polyketide synthase genes and the transportation of dinophysistoxin-4 from chloroplast to vacuoles.

A Review of In Situ Methods-Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) for the Collection and Concentration of Marine Biotoxins and Pharmaceuticals in Environmental Waters

Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) are in situ methods that have been applied to pre-concentrate a range of marine toxins, pesticides and pharmaceutical compounds that occur at low levels in marine and environmental waters. Recent research has identified the widespread distribution of biotoxins and pharmaceuticals in environmental waters (marine, brackish and freshwater) highlighting the need for the development of effective techniques to generate accurate quantitative water system profiles. In this manuscript, we reviewed in situ methods known as Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) for the collection and concentration of marine biotoxins, freshwater cyanotoxins and pharmaceuticals in environmental waters since the 1980s to present. Twelve different adsorption substrates in SPATT and 18 different sorbents in POCIS were reviewed for their ability to absorb a range of lipophilic and hydrophilic marine biotoxins, pharmaceuticals, pesticides, antibiotics and microcystins in marine water, freshwater and wastewater. This review suggests the gaps in reported studies, outlines future research possibilities and guides researchers who wish to work on water contaminates using Solid Phase Adsorption Toxin Tracking (SPATT) and Polar Organic Chemical Integrative Sampler (POCIS) technologies.

Time-Lagged Correlation Analysis of Shellfish Toxicity Reveals Predictive Links to Adjacent Areas, Species, and Environmental Conditions

Diarrhetic Shellfish Poisoning (DSP) is an acute intoxication caused by the consumption of contaminated shellfish, which is common in many regions of the world. To safeguard human health, most countries implement programs focused on the surveillance of toxic phytoplankton abundance and shellfish toxicity levels, an effort that can be complemented by a deeper understanding of the underlying phenomena. In this work, we identify patterns of seasonality in shellfish toxicity across the Portuguese coast and analyse time-lagged correlations between this toxicity and various potential risk factors. We extend the understanding of these relations through the introduction of temporal lags, allowing the analysis of time series at different points in time and the study of the predictive power of the tested variables. This study confirms previous findings about toxicity seasonality patterns on the Portuguese coast and provides further quantitative data about the relations between shellfish toxicity and geographical location, shellfish species, toxic phytoplankton abundances, and environmental conditions. Furthermore, multiple pairs of areas and shellfish species are identified as having correlations high enough to allow for a predictive analysis. These results represent the first step towards understanding the dynamics of DSP toxicity in Portuguese shellfish producing areas, such as temporal and spatial variability, and towards the development of a shellfish safety forecasting system.

In Vitro Interactions between Okadaic Acid and Rat Gut Microbiome

Okadaic acid (OA) is a marine biotoxin associated with diarrhetic shellfish poisoning (DSP), posing some threat to human beings. The oral toxicity of OA is complex, and the mechanism of toxicity is not clear. The interaction between OA and gut microbiota may provide a reasonable explanation for the complex toxicity of OA. Due to the complex environment in vivo, an in vitro study may be better for the interactions between OA and gut microbiome. Here, we conducted an in vitro fermentation experiment of gut bacteria in the presence of 0–1000 nM OA. The remolding ability of OA on bacterial composition was investigated by 16S rDNA sequencing, and differential metabolites in fermentation system with different concentration of OA was detected by LC-MS/MS. We found that OA inhibited some specific bacterial genera but promoted others. In addition, eight possible metabolites of OA, including dinophysistoxin-2 (DTX-2), were detected in the fermentation system. The abundance of Faecalitalea was strongly correlated with the possible metabolites of OA, suggesting that Faecalitalea may be involved in the metabolism of OA in vitro. Our findings confirmed the direct interaction between OA and gut bacteria, which helps to reveal the metabolic process of OA and provide valuable evidence for elucidating the complex toxicity of OA.

Effect of Nitrogen, Phosphorous, and Light Colimitation on Amphidinol Production and Growth in the Marine Dinoflagellate Microalga Amphidinium carterae

The marine dinoflagellate microalga Amphidinium carterae is a source of amphidinols, a fascinating group of polyketide metabolites potentially useful in drug design. However, Amphidinium carterae grows slowly and produces these toxins in tiny amounts, representing a hurdle for large-scale production. Understanding dinoflagellate growth kinetics under different photobioreactor conditions is imperative for promoting the successful implementation of a full-scale integrated bioproduct production system. This study evaluates the feasibility of growing Amphidinium carterae under different ranges of nitrogen concentration (NO₃⁻ = 882–2646 µM), phosphorus concentration (PO₃³⁻ = 181–529 µM), and light intensity (Y₀ = 286–573 µE m⁻² s⁻¹) to produce amphidinols. A mathematical colimitation kinetic model based on the “cell quota” concept is developed to predict both algal growth and nutrient drawdown, assuming that all three variables (nitrogen, phosphorous and light) can simultaneously colimit microalgal growth. The model was applied to the semicontinuous culture of the marine microalgae Amphidinium carterae in an indoor LED-lit raceway photobioreactor. The results show that both growth and amphidinol production strongly depend on nutrient concentrations and light intensity. Nonetheless, it was possible to increase Amphidinium carterae growth while simultaneously promoting the overproduction of amphidinols. The proposed model adequately describes Amphidinium carterae growth, nitrate and phosphate concentrations, and intracellular nitrogen and phosphorus storage, and has therefore the potential to be extended to other systems used in dinoflagellate cultivation and the production of bioproducts obtained therein.

Optimization and Validation of a High Throughput UHPLC-MS/MS Method for Determination of the EU Regulated Lipophilic Marine Toxins and Occurrence in Fresh and Processed Shellfish

Under the name of lipophilic marine toxins, there are included more than 1000 toxic secondary metabolites, produced by phytoplankton, with the common chemical property of lipophilicity. Due to toxicological effects and geographical distribution, in European legislation relevant compounds are regulated, and their determination is accomplished with the reference liquid chromatography-tandem mass spectrometry method. In this study a modified ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) method has been developed for the identification and quantification of EU-regulated lipophilic toxins. The method optimization included a refinement of SPE-C18 clean-up, in order to reduce matrix interferences. Improved LC conditions and upgraded chromatographic ammonia-based gradient ensured the best separation of all analytes and, in particular, of the two structural isomers (OA and DTX2). Also, different MS parameters were tested, and confirmation criteria finally established. The validation studies confirmed that all parameters were satisfactory. The requirements for precision (RSD% < 11.8% for each compound), trueness (recoveries from 73 to 101%) and sensitivity (limits of quantification in the range 3−8 µg kg−1) were fulfilled. The matrix effect, ranging from −9 to 19%, allowed the use of a calibration curve in solvent (3−320 µg kg−1 in matrix) for quantification of real samples. Method relative uncertainty ranged from 12 to 20.3%. Additionally, a total of 1000 shellfish samples was analysed, providing a first preliminary surveillance study that may contribute to the knowledge of lipophilic marine toxins contamination. Increase in algae proliferation events and intoxication cases, EFSA suggestions for modification of maximum permitted levels and toxicity equivalency factors, and new studies of important toxic effects underline that implementation of reference methods still represents an important task for health and food safety laboratories.

Antioxidant responses and okadaic acid accumulation in Laeonereis acuta (Annelida) exposed to the harmful dinoflagellate Prorocentrum cf. lima

We evaluated the accumulation of okadaic acid (OA), a diarrhetic toxin, and the antioxidant responses in the marine annelid Laeonereis acuta exposed to the benthic toxigenic dinoflagellate Prorocentrum cf. lima. Nontoxic Tetraselmis sp. was used as a control diet. Living cells of the two algae were supplied as food to animals kept in agar medium for 72 h. To assess the significance of the observed effects, our experimental design treated the algal species (diet), algal cell densities, and exposure time as fixed factors. Responses of the organisms were assessed through oxidative stress biomarkers (glutathione-S-transferase [GST], catalase [CAT], reduced glutathione [GSH] and lipid peroxidation [LPO]). Toxin accumulation was measured by LC-MS/MS in whole-body homogenates after 12, 24 and 72 h of exposure. Worms exposed to the toxigenic dinoflagellate gradually accumulated OA, with toxin levels directly related to the cell density of Prorocentrum cf. lima. Worms fed with Prorocentrum cf. lima exhibited decreased CAT activity, increased LPO levels - both interactively affected by algal species and time - and decreased GSH levels, which were interactively affected by algal species and cell density. Higher LPO levels, along with the inhibition of CAT and GSH, clearly indicated an oxidative stress situation in worms exposed to the toxigenic dinoflagellate. Laeonereis acuta accumulated moderate OA levels and may act as a vector of OA to food webs in estuarine areas under high Prorocentrum cf. lima abundance.

A Comparative Analysis of Methods (LC-MS/MS, LC-MS and Rapid Test Kits) for the Determination of Diarrhetic Shellfish Toxins in Oysters, Mussels and Pipis

Rapid methods for the detection of biotoxins in shellfish can assist the seafood industry and safeguard public health. Diarrhetic Shellfish Toxins (DSTs) are produced by species of the dinoflagellate genus Dinophysis, yet the comparative efficacy of their detection methods has not been systematically determined. Here, we examined DSTs in spiked and naturally contaminated shellfish–Sydney Rock Oysters (Saccostrea glomerata), Pacific Oysters (Magallana gigas/Crassostrea gigas), Blue Mussels (Mytilus galloprovincialis) and Pipis (Plebidonax deltoides/Donax deltoides), using LC-MS/MS and LC-MS in 4 laboratories, and 5 rapid test kits (quantitative Enzyme-Linked Immunosorbent Assay (ELISA) and Protein Phosphatase Inhibition Assay (PP2A), and qualitative Lateral Flow Assay (LFA)). We found all toxins in all species could be recovered by all laboratories using LC-MS/MS (Liquid Chromatography—tandem Mass Spectrometry) and LC-MS (Liquid Chromatography—Mass Spectrometry); however, DST recovery at low and mid-level concentrations (<0.1 mg/kg) was variable (0–150%), while recovery at high-level concentrations (>0.86 mg/kg) was higher (60–262%). While no clear differences were observed between shellfish, all kits delivered an unacceptably high level (25–100%) of falsely compliant results for spiked samples. The LFA and the PP2A kits performed satisfactorily for naturally contaminated pipis (0%, 5% falsely compliant, respectively). There were correlations between spiked DSTs and quantitative methods was highest for LC-MS (r² = 0.86) and the PP2A kit (r² = 0.72). Overall, our results do not support the use of any DST rapid test kit as a stand-alone quality assurance measure at this time.

Effects of the Marine Biotoxins Okadaic Acid and Dinophysistoxins on Fish

Natural high proliferations of toxin-producing microorganisms in marine and freshwater environments result in dreadful consequences at the socioeconomically and environmental level due to water and seafood contamination. Monitoring programs and scientific evidence point to harmful algal blooms (HABs) increasing in frequency and intensity as a result of global climate alterations. Among marine toxins, the okadaic acid (OA) and the related dinophysistoxins (DTX) are the most frequently reported in EU waters, mainly in shellfish species. These toxins are responsible for human syndrome diarrhetic shellfish poisoning (DSP). Fish, like other marine species, are also exposed to HABs and their toxins. However, reduced attention has been given to exposure, accumulation, and effects on fish of DSP toxins, such as OA. The present review intends to summarize the current knowledge of the impact of DSP toxins and to identify the main issues needing further research. From data reviewed in this work, it is clear that exposure of fish to DSP toxins causes a range of negative effects, from behavioral and morphological alterations to death. However, there is still much to be investigated about the ecological and food safety risks related to contamination of fish with DSP toxins.

Improved Isolation Procedures for Okadaic Acid Group Toxins from Shellfish (Mytilus edulis) and Microalgae (Prorocentrum lima)

Okadaic acid (OA) group toxins may accumulate in shellfish and can result in diarrhetic shellfish poisoning when consumed by humans, and are therefore regulated. Purified toxins are required for the production of certified reference materials used to accurately quantitate toxin levels in shellfish and water samples, and for other research purposes. An improved procedure was developed for the isolation of dinophysistoxin 2 (DTX2) from shellfish (M. edulis), reducing the number of purification steps from eight to five, thereby increasing recoveries to ~68%, compared to ~40% in a previously reported method, and a purity of >95%. Cell densities and toxin production were monitored in cultures of Prorocentrum lima, that produced OA, DTX1, and their esters, over ~1.5 years with maximum cell densities of ~70,000 cells mL⁻¹ observed. Toxin accumulation progressively increased over the study period, to ~0.7 and 2.1 mg L⁻¹ of OA and DTX1 (including their esters), respectively, providing information on appropriate harvesting times. A procedure for the purification of OA and DTX1 from the harvested biomass was developed employing four purification steps, with recoveries of ~76% and purities of >95% being achieved. Purities were confirmed by LC-HRMS, LC-UV, and NMR spectroscopy. Additional stability observations led to a better understanding of the chemistry of these toxins.

The effect of temperature on physiology, toxicity and toxin content of the benthic dinoflagellate Coolia malayensis from a seasonal tropical region

Coolia malayensis is one of the commonly found benthic dinoflagellates in Hong Kong which can produce biotoxins and threaten the early life stages of marine invertebrates. Seawater temperature has been recognized as one of the primary environmental factors that affect the formation of harmful algal blooms. The present study evaluated the responses of C. malayensis, including growth, toxicity and toxin content (putative analogues of okadaic acid and azaspiracids), after exposure to a range of seven different temperatures (i.e., 16°C, 18°C, 20°C, 22°C, 24°C, 26°C, and 28°C). The highest algal density and specific growth rate were recorded at 24°C. Significantly higher F_v/F_m (maximum quantum yield of PSII) and total phaeo-pigment values were observed in the exponential growth phase at 28°C. The toxicity of the algal extract, which was assessed by the lethality rate of Artemia larvae, increased with temperature. The highest toxin content was detected at the second highest temperature treatment, i.e., 26°C. Overall, temperature had significant effects on the physiological activities and toxicity of C. malayensis. This study has raised attention to the potentially increasing risks posed by toxic benthic dinoflagellates during heat waves in coastal waters.

Nontarget Screening and Toxicity Evaluation of Diol Esters of Okadaic Acid and Dinophysistoxins Reveal Intraspecies Difference of Prorocentrum lima

High-resolution mass spectrometry (HRMS) analysis with the assistance of molecular networking was used to investigate intracellular toxin profiles of five Prorocentrum lima (P. lima) strains sampled from the north Yellow Sea and South China Sea. Mice were used as a model species for testing the acute toxicity of intracellular okadaic acid (OA) and dinophysistoxins (DTXs) in free and esterified states. Results showed that OA and DTX1 esterified derivatives were detected in all P. lima samples, accounting for 55%-96% of total toxins in five strains. A total of 24 esters and 1 stereoisomer of DTX1 (35S DTX1) were identified based on molecular networking and MS data analysis, 15 esters of which have been reported first. All P. lima strains displayed specific toxin profiles, and preliminary analysis suggested that toxin profiles of the five P. lima strains might be region-related. Moreover, acute toxicity in mice suggested higher toxicity of esters compared with free toxins, which highlights the importance and urgency of attention to esterified toxins in P. lima.

Bioluminescence and toxicity as driving factors in harmful algal blooms: Ecological functions and genetic variability

Dinoflagellates are an ecologically important group of marine microbial eukaryotes with a remarkable array of adaptive strategies. It is ironic that two of the traits for which dinoflagellates are best known, toxin production and bioluminescence, are rarely linked when considering the ecological significance of either. Although dinoflagellate species that form some of the most widespread and frequent harmful algal blooms (HABs) are bioluminescent, the molecular and eco-evolutionary associations between these two traits has received little attention. Here, the major themes of biochemistry and genetics, ecological functions, signaling mechanisms, and evolution are addressed, with parallels and connections drawn between the two. Of the 17 major classes of dinoflagellate toxins, only two are produced by bioluminescent species: saxitoxin (STX) and yessotoxin. Of these, STX has been extensively studied, including the identification of the STX biosynthetic genes. While numerous theories have been put forward as to the eco-evolutionary roles of both bioluminescence and toxicity, a general consensus is that both function as grazing deterrents. Thus, both bioluminescence and toxicity may aid in HAB initiation as they alleviate grazing pressure on the HAB species. A large gap in our understanding is the genetic variability among natural bloom populations, as both toxic and non-toxic strains have been isolated from the same geographic location. The same applies to bioluminescence, as there exist both bioluminescent and non-bioluminescent strains of the same species. Recent evidence demonstrating that blooms are not monoclonal events necessitates a greater level of understanding as to the genetic variability of these traits among sub-populations as well as the mechanisms by which cells acquire or lose the trait, as sequence analysis of STX+ and STX- species indicate the key gene required for toxicity is lost rather than gained. While the extent of genetic variability for both bioluminescence and toxicity among natural HAB sub-populations remains unknown, it is an area that needs to be explored in order to gain greater insights into the molecular mechanisms and environmental parameters driving HAB evolution.

Degradation of okadaic acid in seawater by UV/TiO2 photocatalysis - Proof of concept

The consumption of contaminated shellfish with marine toxins causes adverse socioeconomical, environmental and health impacts. The marine toxin okadaic acid (OA) provokes diarrhetic shellfish poisoning (DSP) syndrome characterized by severe gastrointestinal symptoms. Therefore, there is increasing interest in removing these toxins from the marine environment to protect shellfish harvesting sites. Photocatalysis is proposed as an efficient method to detoxify the marine environment. In this study, Prorocentrum lima was used to produce high purity DSP toxins, in particular OA, for degradation studies. The profiling, characterization and quantification of DSP toxins in the culture of P. lima were achieved by ultrahigh performance liquid chromatography coupled to quadrupole-time of flight mass spectrometry (UPLC-QTOF-MSE) for accurate-mass full spectrum acquisition data. The effectiveness of UV/TiO2 system to degrade OA in seawater was assessed in lab-scale experiments and identification of transformation products was proposed based on the data obtained during analysis by UPLC-QTOF-MSE. The detoxification potential of the UV/TiO2 system was investigated using the phosphatase inhibition assay. Sufficient amount of high-purity OA (25 mg, >90% purity) was produced in-house for use in photocatalysis experiments by simple reversed-phase flash chromatography. Complete degradation of OA was observed in seawater after 30 min and 7.5 min in deionized water. The rate constants fitted with the pseudo-first order kinetic model (R2 > 0.96). High-resolution mass spectrometry analysis of the photocatalyzed OA allowed tentative identification of four transformation products. Detoxification was achieved in parallel with the degradation of OA in deionized water and artificial ocean water (≤20 min) but not for seawater. Overall, results suggest that UV/TiO2 photocatalysis can be an effective approach for degrading OA and their TPs in the marine environment. To the best of our knowledge, this is the first report on the use of photocatalysis to degrade marine toxins and its promising potential to protect shellfish harvesting sites.

Toxicity and differential oxidative stress effects on zebrafish larvae following exposure to toxins from the okadaic acid group

Okadaic acid-group (OA-group) is a set of lipophilic toxins produced only in seawater by species of the Dinophysis and Prorocentrum genera, and characterized globally by being associated with harmful algal blooms (HABs). The diarrhetic shellfish poisoning toxins okadaic acid (OA) and dinophysistoxin-1 (DTX-1) are the most prevalent toxic analogues making up the OA-group, which jeopardize environmental safety and human health through consumption of hydrobiological organisms contaminated with these toxins that produce diarrhetic shellfish poisoning (DSP) syndrome in humans. Consequently, a regulatory limit of 160 μg of OA-group/kg was established for marine resources (bivalves). The aim of this study was to investigate effects varying concentrations of 1-15 μg/ml OA or DTX-1 on toxicity, development, and oxidative damage in zebrafish larvae (Danio rerio). After determining the lethal concentration 50 (LC₅₀) in zebrafish larvae of 10 and 7 μg/ml (24 h) and effective concentration 50 (EC₅₀) of 8 and 6 μg/ml (24 h), different concentrations (5, 6.5, or 8 μg/ml of OA and 4, 4.5, or 6 μg/ml of DTX-1) were used to examine the effects of these toxins on oxidative damage to larvae at different time points between 24 and 120 hpf. Macroscopic evaluation during the exposure period showed alterations in zebrafish including pericardial edema, cyclopia, shortening in the anteroposterior axis, and developmental delay. The activity levels of biochemical biomarkers superoxide dismutase (SOD) and catalase (CAT) demonstrated a concentration-dependent decrease while glutathione peroxidase (GPx) and glutathione reductase (GR) were markedly elevated. In addition, increased levels of oxidative damage (malondialdehyde and carbonyl content) were detected following toxin exposure. Data demonstrate that high concentrations of OA and DTX-1produced pathological damage in the early stages of development <48 h post-fertilization (hpf) associated with oxidative damage.

Screening-level evaluation of marine benthic dinoflagellates toxicity using mammalian cell lines

Complementary studies at different levels of the biological organization are fundamental to fully link environmental exposure to marine benthic dinoflagellate toxins and their effects. In order to contribute to this transdisciplinary evaluation, and for the first time, the present study aims to study the effects of Gambierdiscus excentricus, Ostreopsis cf. ovata, Prorocentrum hoffmannianum and Prorocentrum lima extracts on seven functionally different mammalian cell lines: HEK 293, HepG2, HNDF, H9c2(2-1), MC3T3-E1, Raw 264.7 and SH-SY5Y. All the cell lines presented cell mass decrease in a concentration-dependence of dinoflagellate extracts, exhibiting marked differences in cell toxicity. Gambierdiscus excentricus presented the highest effect, at very low concentrations with EC_50,24h (i.e., the concentration that gives half-maximal response after a 24-h exposure) between 1.3 and 13 cells mL^-1, followed by O. cf. ovata (EC_50,24h between 3.3 and 40 cells mL^-1), and Prorocentrum species (P. lima: EC_50,24h between 191 and 1027 cells mL^-1 and P. hoffmannianum: EC_50,24h between 152 and 783 cells mL^-1). Cellular specificities were also detected and rat cardiomyoblast H9c2(2-1) cells were in general the most sensitive to dinoflagellate toxic compounds, suggesting that this cell line is an animal-free potential model for dinoflagellate toxin testing. Finally, the sensitivity of cells expressing distinct phenotypes to each dinoflagellate extract exhibited low relation to human poisoning symptoms.

Cytotoxic 4-Hydroxyprorocentrolide and Prorocentrolide C from Cultured Dinoflagellate Prorocentrum lima Induce Human Cancer Cell Death through Apoptosis and Cell Cycle Arrest

Prorocentrolide and its analogs, the novel naturally derived antitumor agents, have recently been identified in the dinoflagellate Prorocentrum lima. In the current study, the underlying inhibitory mechanisms of 4-hydroxyprorocentrolide (1) and prorocentrolide C (2) on the proliferation of human carcinoma cells were determined. 1 and 2 arrested the cell cycle at the S phase in A549 cells and G2/M phase in HT-29 cells, leading to apoptotic cell death, as determined using fluorescence-activated cell sorting analysis with Annexin V/PI double staining. Apoptosis induced by these compounds was associated with alterations in the expression of cell cycle-regulating proteins (cyclin D1, cyclin E1, CDK2, and CDK4), as well as alterations in the levels of apoptosis-related proteins (PPAR, Bcl-2, Bcl-xl, and survivin). These findings provide new insights into the antitumor mechanisms of 4-hydroxyprorocentrolide and prorocentrolide C and a basis for future investigations assessing prorocentrolide analogs as prospective therapeutic drugs.

De novo transcriptome analysis of the mussel Perna viridis after exposure to the toxic dinoflagellate Prorocentrum lima

Diarrheic shellfish poisoning (DSP) toxins are produced by harmful microalgae and accumulate in bivalve mollusks, causing various toxicity. These toxic effects appear to abate with increasing DSP concentration and longer exposure time, however, the underlying mechanisms remain unclear. To explore the underlying molecular mechanisms, de novo transcriptome analysis of the digestive gland of Perna viridis was performed after Prorocentrum lima exposure. RNA-seq analysis showed that 1886 and 237 genes were up- and down-regulated, respectively after 6 h exposure to P. lima, while 265 genes were up-regulated and 217 genes were down-regulated after 96 h compared to the control. These differentially expressed genes mainly involved in Nrf2 signing pathways, immune stress, apoptosis and cytoskeleton, etc. Combined with qPCR results, we speculated that the mussel P. viridis might mainly rely on glutathione S-transferase (GST) and ABC transporters to counteract DSP toxins during short-term exposure. However, longer exposure of P. lima could activate the Nrf2 signaling pathway and inhibitors of apoptosis protein (IAP), which in turn reduced the damage of DSP toxins to the mussel. DSP toxins could induce cytoskeleton destabilization and had some negative impact on the immune system of bivalves. Collectively, our findings uncovered the crucial molecular mechanisms and the regulatory metabolic nodes that underpin the defense mechanism of bivalves against DSP toxins and also advanced our current understanding of bivalve defense mechanisms.

Distribution and potential toxicity of benthic harmful dinoflagellates in waters of Florida Bay and the Florida Keys

Few studies have been carried out on benthic dinoflagellates along the Florida Keys, and little is known about their distribution or toxicity in Florida Bay. Here, the distribution and abundance of benthic dinoflagellates was explored in northern and eastern Florida Bay and along the bay and ocean sides of the Florida Keys. Isolates were brought into culture and their toxicity was tested with oyster larvae bioassays. Seven genera were detected, including Prorocentrum, Coolia, Ostreopsis, Amphidinium, Gambierdiscus, Fukuyoa (all included potentially toxic species) and Sinophysis. In general, distribution increased with water temperature and nutrient availability, especially that of phosphate. This study documented the first record of Coolia santacroce in the Florida Keys. Potential toxic effects of Gambierdiscus caribaeus, the abundance of which exceeded 1000 cells g^-1 fw at some sites, were established using oyster larvae as a bioassay organism. These findings suggest a potential risk of ciguatera fish poisoning in this area.

ABC Transporters in Prorocentrum lima and Their Expression Under Different Environmental Conditions Including Okadaic Acid Production

Prorocentrum lima is a typical benthic toxic dinoflagellate, which can produce phycotoxins such as okadaic acid (OA). In this study, we identified three ABC transporter genes (ABCB1, ABCC1 and ABCG2) and characterized their expression patterns, as well as OA production under different environmental conditions in P. lima. We found that the three ABC transporters all showed high identity with related ABC proteins from other species, and contained classical features of ABC transport proteins. Among them, ABCG2 was a half size transporter. The three ABC transporter genes displayed various expression profiles under different conditions. The high concentration of Cu²⁺ could up-regulate ABCB1, ABCC1 and ABCG2 transcripts in P. lima, suggesting the potential defensive role of ABC transporters against metal ions in surrounding waters. Cu²⁺, in some concentration, could induce OA production; meanwhile, tributyltin inhibited OA accumulation. The grazer Artemia salina could induce OA production, and P. lima displayed some toxicity to the grazer, indicating the possibility of OA as an anti-grazing chemical. Collectively, our results revealed intriguing data about OA production and the expression patterns of three ABC transporter genes. However, we could not find any significant correlation between OA production and expression pattern of the three ABC transporters in P. lima. Our results might provide new molecular insights on the defensive responses of P. lima to the surrounding environment.

Spatio-temporal dynamics and biotic substrate preferences of benthic dinoflagellates in the Lesser Antilles, Caribbean sea

Epibenthic dinoflagellates were monitored monthly over an 18 month period in Guadeloupe and Martinique (Lesser Antilles, Caribbean Sea). These islands are located in the second most affected ciguatera fish poisoning (CFP) region of the world. Guadeloupe presented five times more total epibenthic dinoflagellates and two times less abundant Gambierdiscus spp. compared to Martinique, although the area of frequent CFP outbreaks covers Guadeloupe and not Martinique. Results did not show any clear seasonal variations of benthic dinoflagellates abundances. Temperature and salinity were not driving parameters in the evolution of total benthic dinoflagellate abundances. Preferential associations were found between macrophyte species and epibenthic dinoflagellates. The Phaeophyceae Dictyota spp. hosted the highest abundances of total epibenthic dinoflagellates, composed mainly of Ostrepsis and Prorocentrum genera. The seagrass Halophila stipulacea hosted the highest abundances of Gambierdiscus spp. and Sinophysis spp. whilst the highest abundance of Coolia was determined on Galaxaura spp. The pelagic Sargassum spp. hosted the lowest abundances of benthic dinoflagellates including the genus Gambierdiscus.

Role of temperature and nutrients on the growth and toxin production of Prorocentrum hoffmannianum (Dinophyceae) from the Florida Keys

The benthic dinoflagellate Prorocentrum hoffmannianum M.A. Faust is typical of tropical warm waters and produces biotoxins responsible for diarrhetic shellfish poisoning (DSP). In this study, the effect of temperature and nutrient limitation on growth and toxin production of P. hoffmannianum isolated from field samples collected in the Florida Keys was investigated. Batch culture experiments were ran at two temperatures (i.e. 21 ± 0.1 and 27 ± 0.1 °C) and under nitrogen-limited (14.7 μmol L^-1 N-NO₃- and 18.1 μmol L^-1 P-PO₄^3-) and phosphorus-limited (441 μmol L^-1 N-NO₃- and 0.6 μmol L^-1 P-PO₄^3-) levels with respect to control nutrient conditions (441 μmol L^-1 N-NO₃-and 18.1 μmol L^-1 P-PO₄^3-). Both temperature and nutrient conditions significantly affected growth rates and maximum yield of P. hoffmannianum with the maximum values being recorded at the higher temperature and in the replete medium. Production of okadaic acid was induced under all conditions (from 13.5 to 859.8 pg cell^-1), with values up to one order of magnitude higher than those observed in other DSP toxin producing species. Toxin production was enhanced under P limitation at 27 °C, corroborating the theory that toxin production is modulated by cell physiological conditions, which are in turn affected by a wide spectrum of factors, including environmental stressors such as nutrient availability. Toxin fraction released in the growth medium was negligible. No okadaic acid esters were detected in this strain of P. hoffmannianum.

Spatial and seasonal variation of diarrheic shellfish poisoning (DSP) toxins in bivalve mollusks from some coastal regions of Vietnam and assessment of potential health risks

The occurrence of okadaic acid (OA) group toxins in bivalve mollusk collected from Vietnamese coastal areas was investigated from April 2016 to April 2017. OA group toxins were detected in mollusk by UPLC-MS/MS with the highest level of 11.3 ng/g and detection frequency of 11.8%. Toxins were detected more frequently in dry season (14.4% of analyzed samples) than in wet season (7.9%). Toxins were also detected more frequently at sampling locations in the northern parts (≥10.4%) than in the southern part (≤8.3%) of Vietnamese coastline. Results of this study were similar to those obtained in long-term studies in regions geographically close to Vietnam, confirming decisive influence of geographic location on the accumulation of toxins in mollusks. Within the scope of the study, toxin levels in all contaminated samples were below the regulation limit (160 ng/g), but the presence of OA group toxins in bivalve mollusk suggests the need of a more stringent control of toxins in bivalve mollusk in Vietnam.

Prorocentrolide-A from Cultured Prorocentrum lima Dinoflagellates Collected in Japan Blocks Sub-Types of Nicotinic Acetylcholine Receptors

Prorocentrolides are members of the cyclic imine phycotoxins family. Their chemical structure includes a 26-membered carbo-macrocycle and a 28-membered macrocyclic lactone arranged around a hexahydroisoquinoline that incorporates the characteristic cyclic imine group. Six prorocentrolides are already known. However, their mode of action remains undetermined. The aim of the present work was to explore whether prorocentrolide-A acts on nicotinic acetylcholine receptors (nAChRs), using competition-binding assays and electrophysiological techniques. Prorocentrolide-A displaced [¹²⁵I]α-bungarotoxin binding to Torpedo membranes, expressing the muscle-type (α1₂β1γδ) nAChR, and in HEK-293 cells, expressing the chimeric chick neuronal α7-5HT₃ nAChR. Functional studies revealed that prorocentrolide-A had no agonist action on nAChRs, but inhibited ACh-induced currents in Xenopus oocytes that had incorporated the muscle-type α1₂β1γδ nAChR to their membranes, or that expressed the human α7 nAChR, as revealed by voltage-clamp recordings. Molecular docking calculations showed the absence of the characteristic hydrogen bond between the iminium group of prorocentrolide-A and the backbone carbonyl group of Trp147 in the receptor, explaining its weaker affinity as compared to all other cyclic imine toxins. In conclusion, this is the first study to show that prorocentrolide-A acts on both muscle and neuronal nAChRs, but with higher affinity on the muscle-type nAChR.

Biotechnological and Pharmacological Applications of Biotoxins and Other Bioactive Molecules from Dinoflagellates

The long-lasting interest in bioactive molecules (namely toxins) produced by (microalga) dinoflagellates has risen in recent years. Exhibiting wide diversity and complexity, said compounds are well-recognized for their biological features, with great potential for use as pharmaceutical therapies and biological research probes. Unfortunately, provision of those compounds is still far from sufficient, especially in view of an increasing demand for preclinical testing. Despite the difficulties to establish dinoflagellate cultures and obtain reasonable productivities of such compounds, intensive research has permitted a number of advances in the field. This paper accordingly reviews the characteristics of some of the most important biotoxins (and other bioactive substances) produced by dinoflagellates. It also presents and discusses (to some length) the main advances pertaining to dinoflagellate production, from bench to large scale-with an emphasis on material published since the latest review available on the subject. Such advances encompass improvements in nutrient formulation and light supply as major operational conditions; they have permitted adaptation of classical designs, and aided the development of novel configurations for dinoflagellate growth-even though shearing-related issues remain a major challenge.

Profiling of Extracellular Toxins Associated with Diarrhetic Shellfish Poison in Prorocentrum lima Culture Medium by High-Performance Liquid Chromatography Coupled with Mass Spectrometry

Extracellular toxins released by marine toxigenic algae into the marine environment have attracted increasing attention in recent years. In this study, profiling, characterization and quantification of extracellular toxin compounds associated with diarrhetic shellfish poison (DSP) in the culture medium of toxin-producing dinoflagellates were performed using high-performance liquid chromatography–high-resolution mass spectrometry/tandem mass spectrometry for the first time. Results showed that solid-phase extraction can effectively enrich and clean the DSP compounds in the culture medium of Prorocentrum lima (P. lima), and the proposed method achieved satisfactory recoveries (94.80%–100.58%) and repeatability (relative standard deviation ≤9.27%). Commercial software associated with the accurate mass information of known DSP toxins and their derivatives was used to screen and identify DSP compounds. Nine extracellular DSP compounds were identified, of which seven toxins (including OA-D7b, OA-D9b, OA-D10a/b, and so on) were found in the culture medium of P. lima for the first time. The results of quantitative analysis showed that the contents of extracellular DSP compounds in P. lima culture medium were relatively high, and the types and contents of intracellular and extracellular toxins apparently varied in the different growth stages of P. lima. The concentrations of extracellular okadaic acid and dinophysistoxin-1 were within 19.9–34.0 and 15.2–27.9 μg/L, respectively. The total concentration of the DSP compounds was within the range of 57.70–79.63 μg/L. The results showed that the proposed method is an effective tool for profiling the extracellular DSP compounds in the culture medium of marine toxigenic algae.