BMAA in shellfish from two Portuguese transitional water bodies suggests the marine dinoflagellate Gymnodinium catenatum as a potential BMAA source

The neurotoxin β-N-methylamino-l-alanine (BMAA) and its putative role in multiple neurodegenerative diseases have been intensely studied since 2005 when the toxin was discovered to be produced by worldwide-distributed cyanobacterial species inhabiting terrestrial, marine, brackish, and freshwater ecosystems. Recently, BMAA production was also associated with one eukaryotic group, namely, diatoms, raising questions about its production by other phytoplanktonic groups. To test for BMAA bioavailability in ecosystems where abundant phytoplanktonic blooms regularly occur, samples of filter-feeding shellfish were collected in two Portuguese transitional water bodies. BMAA content in cockles (Cerastoderma edule) collected weekly between September and November 2009 from Ria de Aveiro and at least once a month from May to November from Ria Formosa, fluctuated from 0.079±0.055 to 0.354±0.066μg/g DW and from below the limit of detection to 0.434±0.110μg/g DW, respectively. Simultaneously to BMAA occurrence in cockles, paralytic shellfish toxins were detected in shellfish as a result of Gymnodinium catenatum blooms indicating a possible link between this marine dinoflagellate and BMAA production. Moreover, considerable high BMAA levels, 0.457±0.186μg/g DW, were then determined in a laboratory grown culture of G. catenatum. This work reveals for the first time the presence of BMAA in shellfish from Atlantic transitional water bodies and consubstantiate evidences of G. catenatum as one of the main sources of BMAA in these ecosystems.

First detection of tetrodotoxin and high levels of paralytic shellfish poisoning toxins in shellfish from Sicily (Italy) by three different analytical methods

Paralytic shellfish toxins (PST) and tetrodotoxin (TTX) are naturally-occurring toxins that may contaminate the food chain, inducing similar neurological symptoms in humans. They are co-extracted under the same conditions and thus their combined detection is desirable. Whilst PST are regulated and officially monitored in Europe, more data on TTX occurrence in bivalves and gastropods are needed before meaningful regulations can be established. In this study, we used three separate analytical methods - pre-column oxidation with liquid chromatography and fluorescence detection, ultrahigh performance hydrophilic interaction liquid chromatography (HILIC) tandem mass spectrometry (MS/MS) and HILIC high resolution (HR) MS/MS - to investigate the presence of PST and TTX in seawater and shellfish (mussels, clams) collected in spring summer 2015 to 2017 in the Mediterranean Sea. Samples were collected at 10 sites in the Syracuse Bay (Sicily, Italy) in concomitance with a mixed bloom of Alexandrium minutum and A. pacificum. A very high PST contamination in mussels emerged, unprecedentedly found in Italy, with maximum total concentration of 10851 μg saxitoxin equivalents per kg of shellfish tissue measured in 2016. In addition, for the first time TTX was detected in Italy in most of the analysed samples in the range 0.8-6.4 μg TTX eq/kg. The recurring blooms of PST-producing species over the 3-year period, the high PST levels and the first finding of TTX in mussels from the Syracuse bay, suggest that monitoring programmes of PST and TTX in seafood should be activated in this geographical area.

Paralytic shellfish toxin biosynthesis in cyanobacteria and dinoflagellates: A molecular overview

Paralytic shellfish toxins (PSTs) are a group of water soluble neurotoxic alkaloids produced by two different kingdoms of life, prokaryotic cyanobacteria and eukaryotic dinoflagellates. Owing to the wide distribution of these organisms, these toxic secondary metabolites account for paralytic shellfish poisonings around the world. On the other hand, their specific binding to voltage-gated sodium channels makes these toxins potentially useful in pharmacological and toxicological applications. Much effort has been devoted to the biosynthetic mechanism of PSTs, and gene clusters encoding 26 proteins involved in PST biosynthesis have been unveiled in several cyanobacterial species. Functional analysis of toxin genes indicates that PST biosynthesis in cyanobacteria is a complex process including biosynthesis, regulation, modification and export. However, less is known about the toxin biosynthesis in dinoflagellates owing to our poor understanding of the massive genome and unique chromosomal characteristics [1]. So far, few genes involved in PST biosynthesis have been identified from dinoflagellates. Moreover, the proteins involved in PST production are far from being totally explored. Thus, the origin and evolution of PST biosynthesis in these two kingdoms are still controversial. In this review, we summarize the recent progress on the characterization of genes and proteins involved in PST biosynthesis in cyanobacteria and dinoflagellates, and discuss the standing evolutionary hypotheses concerning the origin of toxin biosynthesis as well as future perspectives in PST biosynthesis.

SCIENTIFIC QUESTION

Paralytic shellfish toxins (PSTs) are a group of potent neurotoxins which specifically block voltage-gated sodium channels in excitable cells and result in paralytic shellfish poisonings (PSPs) around the world. Two different kingdoms of life, cyanobacteria and dinoflagellates are able to produce PSTs. However, in contrast with cyanobacteria, our understanding of PST biosynthesis in dinoflagellates is extremely limited owing to their unique features. The origin and evolution of PST biosynthesis in these two kingdoms are still controversial.

TECHNICAL SIGNIFICANCE

High-throughput omics technologies, such as genomics, transcriptomics and proteomics provide powerful tools for the study of PST biosynthesis in cyanobacteria and dinoflagellates, and have shown their powerful potential with regard to revealing genes and proteins involved in PST biosynthesis in two kingdoms.

SCIENTIFIC SIGNIFICANCE

This review summarizes the recent progress in PST biosynthesis in cyanobacteria and dinoflagellates with focusing on the novel insights from omics technologies, and discusses the evolutionary relationship of toxin biosynthesis genes between these two kingdoms.

Exposure to toxic Alexandrium minutum activates the detoxifying and antioxidant systems in gills of the oyster Crassostrea gigas

Harmful algal blooms of Alexandrium spp. dinoflagellates regularly occur in French coastal waters contaminating shellfish. Studies have demonstrated that toxic Alexandrium spp. disrupt behavioural and physiological processes in marine filter-feeders, but molecular modifications triggered by phycotoxins are less well understood. This study analyzed the mRNA levels of 7 genes encoding antioxidant/detoxifying enzymes in gills of Pacific oysters (Crassostrea gigas) exposed to a cultured, toxic strain of A. minutum, a producer of paralytic shellfish toxins (PST) or fed Tisochrysis lutea (T. lutea, formerly Isochrysis sp., clone Tahitian (T. iso)), a non-toxic control diet, in four repeated experiments. Transcript levels of sigma-class glutathione S-transferase (GST), glutathione reductase (GR) and ferritin (Fer) were significantly higher in oysters exposed to A. minutum compared to oysters fed T. lutea. The detoxification pathway based upon glutathione (GSH)-conjugation of toxic compounds (phase II) is likely activated, and catalyzed by GST. This system appeared to be activated in gills probably for the detoxification of PST and/or extra-cellular compounds, produced by A. minutum. GST, GR and Fer can also contribute to antioxidant functions to prevent cellular damage from increased reactive oxygen species (ROS) originating either from A. minutum cells directly, from oyster hemocytes during immune response, or from other gill cells as by-products of detoxification.

Dynamics of paralytic shellfish toxins and their metabolites during timecourse exposure of scallops Chlamys farreri and mussels Mytilus galloprovincialis to Alexandrium pacificum

New C-11 hydroxyl metabolites of paralytic shellfish toxins (PSTs) have been reported in shellfish. To gain further information on these metabolites, as well as the potential for formation of phase-II metabolites and acyl esters of PSTs, bivalves were fed with the PSTs-producing dinoflagellate Alexandrium pacificum (strain ATHK). Through independent experiments, scallops (Chlamys farreri) were fed for 9 days and mussels (Mytilus galloprovincialis) for 5 days plus an additional 5 days of depuration, with representative samples taken throughout. Several common PSTs (C1-4, GTX1-6 and NEO) and metabolites including M1, M3, M5, M7, M9, M2 and M8 were detected in the hepatopancreas of scallops during toxin accumulation and in the hepatopancreas of mussels during both toxin accumulation and elimination periods. The relative molar ratio of metabolites to precursor molecules was used to estimate relative metabolic conversion rates. Conversion rates of C1/2 and GTX2/3 were higher than those of C3/4 and GTX1/4, in scallops and mussels. The first metabolites observed in both bivalve species investigated were M1/3, which are formed from C1/2. However, the conversion of GTX2/3 to M2 was more complete than other biotransformation reactions in both mussels and scallops. In general, metabolic conversion of PSTs was observed after a shorter time and to a greater extent in mussels than in scallops in the exposure period. No acyl esters or conjugation products of PSTs with glucuronic acid, glutathione, cysteine and taurine were detected by liquid chromatography with high resolution tandem mass spectrometry in the samples investigated. Additionally, only GTX1/4 and GTX2/3 were detected in the kidney of scallops, which demonstrates that PSTs are mainly metabolized through the hepatic metabolism pathway in bivalves. This work improves the understanding of PST metabolism during toxin accumulation and depuration in commercially harvested shellfish.

Toxic dinoflagellate blooms of Gymnodinium catenatum and their cysts in Taiwan Strait and their relationship to global populations

Gymnodinium catenatum is able to produce paralytic shellfish toxins (PSTs) and was responsible for a massive bloom in the Taiwan Strait, East China Sea, in June 2017, which resulted in serious human poisoning and economic losses. To understand the origin of the bloom and determine the potential for blooms in subsequent years, water and sediment samples collected in the Taiwan Strait from 2016 to 2019 were analyzed for cells and cysts using light microscopy (LM) and/or quantitative polymerase chain reaction (qPCR). The morphology of both cells and cysts from the field and cultures was examined with LM and scanning electron microscopy (SEM). Large subunit (LSU) and/or internal transcribed spacer (ITS)-5.8S rRNA gene sequences were obtained in 13 isolates from bloom samples and five strains from cysts. In addition, cells of strains TIO523 and GCLY02 (from the Taiwan Strait and Yellow Sea of China, respectively) were subjected to growth experiments, and cysts from the field were used for germination experiments under various temperatures. Our strains shared identical LSU and ITS-5.8S rRNA gene sequences with those from other parts of the world, and therefore belonged to a global population. A low abundance of G. catenatum cells were detected during most of the sampling period, but a small bloom was encountered in Quanzhou on June 8, 2018. Few cysts were observed in 2016 but a marked increase was observed after the bloom in 2017, with a highest density of 689 cysts cm^-3. Cysts germinated at temperatures between 14 and 23 °C with a final germination rate over 93%. Strains TIO523 and GCLY02 displayed growth at temperatures between 17 and 26 °C and 14 and 26 °C, respectively, with both strains displaying the highest growth rate of ca. 0.5 divisions d^-1 at 23 °C. The PSTs of the three strains and cysts from the sediments were analyzed by liquid chromatography with tandem mass spectrometry (LC-MS/MS). All strains were able to produce PSTs, which were dominated by N-sulfocarbamoyl C toxins (C1/2, 53.0-143.5 pg cell^-1) and decarbamoyl gonyautoxins (dcGTX2/3, 26.7-52.1 pg cell^-1), although they were not detected in cysts. However, hydroxybenzoyl (GC) toxins were detected in both cells and cysts. Our results suggested that the population in the Taiwan Strait belonged to a warm water ecotype and has a unique toxin profile. Our results also suggested that the persistence of cells in the water column may have initiated the bloom.

Separate and combined effects of neurotoxic and lytic compounds of Alexandrium strains on Mytilus edulis feeding activity and hemocyte function

Multiple toxic and bioactive compounds produced by Alexandrium spp. cause adverse effects on bivalves, but these effects are frequently difficult to attribute to a single compound class. To disentangle the effect of neurotoxic vs lytic secondary metabolites, we exposed blue mussels to either a paralytic shellfish toxin (PST) producing Alexandrium spp. strain, or to an exclusively lytic compound (LC) producing strain, or a strain containing both compound classes, to evaluate the time dependent effects after 3 and 7 days of feeding. Tested parameters comprised signs of paralysis, feeding activity, and immune cell integrity (hemocyte numbers and viability; lysosomal membrane destabilization) and function (ROS production). Both compound classes caused paralysis and immune impairment. The only effect attributable exclusively to PST was increased phagocytic activity after 3 days and impaired feeding activity after 7 days, which curtailed toxin accumulation in digestive glands. Lysosomal membrane destabilization were more closely, but not exclusively, matched with LC exposure. Effects on circulating hemocyte integrity and immune related functions were mostly transient or remained stable within 7 days; except for increased lysosomal labialization and decreased extracellular ROS production when mussels were exposed to the toxin combination. M. edulis displays adaptive fitness traits to survive and maintain immune capacity upon prolonged exposure to environmentally relevant concentrations of PST and/or LC producing Alexandrium strains.

Screening of cyclic imine and paralytic shellfish toxins in isolates of the genus Alexandrium (Dinophyceae) from Atlantic Canada

The dinoflagellate genus Alexandrium Halim has frequently been associated with harmful algal blooms. Although a number of species from this genus are known to produce paralytic shellfish toxins (PST) and/or cyclic imines (CI), studies on comprehensive toxin profiling using techniques capable of detecting the full range of PST and CI analogues are limited. Isolates of Alexandrium spp. from Atlantic Canada were analyzed by targeted and untargeted liquid chromatography-tandem mass spectrometry (LC-MS). Results showed a number of distinct profiles and wide ranging cell quotas of PST and spirolides (SPX) in both A. catenella (Whedon & Kofoid) Balech and A. ostenfedii (Paulsen) Balech & Tangen. The concentration of PST in A. catenella ranged from 0.0029 to 54 fmol cell^-1 with the major components being C2 and GTX4. In addition, putative PST metabolites were confirmed for the first time in A. catenella by high resolution MS/MS. By comparison, A. ostenfeldii isolates showed much lower concentrations of PST (<LOD to 2 fmol cell^-1) and high total levels of SPX (14 to 43 fmol cell^-1). The SPX profile of the A. ostenfeldii strains mainly included 13-desmethyl SPX-C, SPX-C and 20-methyl SPX-G, with low levels of other SPX and gymnodimine-like analogues detected by untargeted -high-resolution LC-MS. This work demonstrates the importance of using screening methods capable of detecting the full suite of PST and CI compounds when analyzing Alexandrium isolates for toxin production and adds further complexity to the known toxin profiles of this genus.

Distinctly different behavioral responses of a copepod, Temora longicornis, to different strains of toxic dinoflagellates, Alexandrium spp

Zooplankton responses to toxic algae are highly variable, even towards taxonomically closely related species or different strains of the same species. Here, the individual level feeding behavior of a copepod, Temora longicornis, was examined which offered 4 similarly sized strains of toxic dinoflagellate Alexandrium spp. and a non-toxic control strain of the dinoflagellate Protoceratium reticulatum. The strains varied in their cellular toxin concentration and composition and in lytic activity. High-speed video observations revealed four distinctly different strain-specific feeding responses of the copepod during 4h incubations: (i) the 'normal' feeding behavior, in which the feeding appendages were beating almost constantly to produce a feeding current and most (90%) of the captured algae were ingested; (ii) the beating activity of the feeding appendages was reduced by ca. 80% during the initial 60min of exposure, after which very few algae were captured and ingested; (iii) capture and ingestion rates remained high, but ingested cells were regurgitated; and (iv) the copepod continued beating its appendages and captured cells at a high rate, but after 60min, most captured cells were rejected. The various prey aversion responses observed may have very different implications to the prey and their ability to form blooms: consumed but regurgitated cells are dead, captured but rejected cells survive and may give the prey a competitive advantage, while reduced feeding activity of the grazer may be equally beneficial to the prey and its competitors. These behaviors were not related to lytic activity or overall paralytic shellfish toxins (PSTs) content and composition and suggest that other cues are responsible for the responses.

Effect of temperature on growth and paralytic toxin profiles in isolates of Gymnodinium catenatum (Dinophyceae) from the Pacific coast of Mexico

The effects of temperature on growth, cell toxicity, toxin content, and profile of paralytic shellfish toxins was determined in eight isolates of Gymnodinium catenatum from several localities along the Pacific Coast of Mexico. The isolates were cultivated in modified f/2 media with Se (10(-8) M), and a reduced concentration of Cu (10(-8) M), under a 12 h:12 h day-night cycle with an irradiance of 150 μE m(-2) s(-1). Isolates were progressively adapted for three generations to each of the temperatures (16, 19, 22, 24, 27, 30, and 33 °C). The cultures were grown in 125 mL Erlenmeyer flasks with 60 mL of media and harvested by filtration in late exponential growth. Toxins were analyzed by HPLC with a post-column oxidation and fluorescent detection (FLD). G. catenatum isolates tolerate temperatures between 16 and 33 °C, with maximum growth rates of 0.32 and 0.39 div day(-1) at 21 °C and 24 °C, respectively; maximum cell densities of 4700 and 5500 cells mL(-1) were obtained at 27 and 21 °C, respectively. No effect of toxicity per cell with temperature was observed, varying between 10.10 and 28.19 pgSXTeq cell(-1). Ten saxitoxin analogues were detected in all isolates, observing changes in the toxin profile with temperature. C1/2 toxins decreased from 80% mol at 16 °C to 20% mol at 33 °C, B1/2 toxins increased from 19% mol at 16 °C to 42% mol at 33 °C, and decarbamoyl toxins were more abundant at 21 °C. These results show that G. catenatum isolates from different regions of the Pacific coast of Mexico have a similar response to temperature and that this parameter can modify growth rate, cell density, and toxin profile of the species, particularly the decarbamoyl and sulfocarbamoyl toxins.

Biokinetics and biotransformation of paralytic shellfish toxins in different tissues of Yesso scallops, Patinopecten yessoensis

Paralytic shellfish toxins (PSTs) are a group of natural toxic substances often found in marine bivalves. Accumulation, anatomical distribution, biotransformation and depuration of PSTs in different tissues of bivalves, however, are still not very well understood. In this study, we investigated biokinetics and biotransformation of PSTs in six different tissues, namely gill, mantle, gonad, adductor muscle, kidney, and digestive gland, in Yesso scallops Patinopecten yessoensis exposed to a toxic strain of dinoflagellate Alexandrium pacificum. High daily accumulation rate (DAR) was recorded at the beginning stage of the experiment. Most of the PSTs in toxic algae ingested by scallops were retained and the toxicity level of PSTs in scallops exceeded the regulatory limit within 5 days. At the late stage of the experiment, however, DAR decreased obviously due to the removal of PSTs. Fitting results of the biokinetics model indicated that the amount of PSTs transferred from digestive gland to mantle, adductor muscle, gonad, kidney, and gill in a decreasing order, and adductor muscle, kidney, and gonad had higher removal rate than gill and mantle. Toxin profile in digestive gland was dominated by N-sulfocarbamoyl toxins 1/2 (C1/2), closely resembled that of the toxic algae. In contrast, toxin components in kidney were dominated by high-potency neosaxitoxin (NEO) and saxitoxin (STX), suggesting that the kidney be a major organ for transformation of PSTs.

Toxin- and species-dependent regulation of ATP-binding cassette (ABC) transporters in scallops after exposure to paralytic shellfish toxin-producing dinoflagellates

ATP-binding cassette (ABC) transporters are membrane-bound proteins involved in exporting various xenobiotic compounds from living cells. Bivalve mollusks can accumulate large amounts of paralytic shellfish toxins (PSTs) from marine dinoflagellates. For aquatic invertebrates, the importance of ABC proteins in multi-xenobiotic resistance has been demonstrated, however, the systematic identification of ABC transporters is very limited. In this study, 64 and 67 ABC genes containing all eight described subfamilies (A to H) were identified in Yesso scallop (Patinopecten yessoensis) and Zhikong scallop (Chlamys farreri), respectively, with massive gene expansion being observed in the ABCC and ABCG subfamilies. The kidney harbored more specifically expressed ABC genes than other organs/tissues, most of which belonged to ABCB, ABCC, and ABCG subfamilies. After feeding the scallops with PST-producing dinoflagellates, the expression of scallop ABC genes in the kidney was regulated in toxin- and species-dependent manners. In total, 20 and 24 ABC genes in Zhikong scallop (CfABCs) were induced after exposure to Alexandrium minutum and A. catenella, with the up-regulated members from both ABCC and ABCG subfamilies mainly showing acute and chronic induction by A. minutum and A. catenella, respectively, while the up-regulated CfABCBs mainly showing chronic induction by both dinoflagellates. In Yesso scallop, only eight ABC genes (PyABCs) were regulated after A. catenella exposure, and all the five up-regulated PyABCs were acutely induced. Our findings imply the functional diversity of scallop ABC genes in coping with PST accumulation, which may contribute to the lineage-specific adaptation of scallops for dealing with algal toxins challenge.

Toxin production of dinoflagellate Gymnodinium catenatum isolated from the East China Sea

Dinoflagellate Gymnodinium catenatum is an important producer of paralytic shellfish toxins (PSTs), including a novel group of hydroxybenzoate derivatives named GC toxins. In the East China Sea, G. catenatum has been considered as the causative agent for several paralytic shellfish poisoning (PSP) episodes, yet the knowledge on their toxin production was still quite limited. In this study, toxins produced by a strain of G. catenatum (MEL11) isolated from the East China Sea were determined, using high performance liquid chromatography coupled with tandem mass spectrometry (HPLC-MS/MS). Changes of toxin profile in the stain MEL11 in response to nutrient and temperature variations were also examined. A total of 11 PST components dominated by hydroxybenzoate analogs and N-sulfocarbamoyl toxins were detected, which was different from other G. catenatum strains previously established in the East China Sea in the presence of GC5 and the lack of dcGTX2&3. Cellular toxin composition and content of the strain had no apparent change within a range of temperature from 20°C to 26°C. In contrast, nutrient limitation and nitrogen source had notable impacts on toxin production. The molar percentage of GC toxins decreased remarkably at the stationary growth phase under nutrient-deprived conditions of both nitrogen (N) and phosphorus (P). The replacement of nitrate with ammonium as the source of N significantly promoted PST production by G. catenatum. The study revealed the potential diversity of toxin profiles of G. catenatum in the East China Sea, and highlighted the effects of nutrients on production of GC toxins by G. catenatum.

Distributions of three Alexandrium species and their toxins across a salinity gradient suggest an increasing impact of GDA producing A. pseudogonyaulax in shallow brackish waters of Northern Europe

Blooms of Alexandrium spp. are a well-known phenomenon in Northern European waters. While A. tamarense/catenella, and A. pseudogonyaulax have been reported from marine waters, high densities of A. ostenfeldii are mainly observed at lower salinities in North Sea estuaries and the Baltic Sea, suggesting salinity as a driver of Alexandrium species composition and toxin distribution. To investigate this relationship, an oceanographic expedition through a natural salinity gradient was conducted in June 2016 along the coasts of Denmark. Besides hydrographic data, phytoplankton and sediment samples were collected for analyses of Alexandrium spp. cell and cyst abundances, for toxin measurement and cell isolation. Plankton data revealed the predominance of A. pseudogonyaulax at all transect stations while A. ostenfeldii and A. catenella generally contributed a minor fraction to the Alexandrium community. High abundances of A. pseudogonyaulax in the shallow enclosed Limfjord were accompanied by high amounts of goniodomin A (GDA). This toxin was also detected at low abundances along with A. pseudogonyaulax in the North Sea and the Kattegat. Genetic and morphological characterization of established strains showed high similarity of the Northern European population to distant geographic populations. Despite low cell abundances of A. ostenfeldii, different profiles of cycloimines were measured in the North Sea and in the Limfjord. This field survey revealed that salinity alone does not determine Alexandrium species and toxin distribution, but emphasizes the importance of habitat conditions such as proximity to seed banks, shelter, and high nutrient concentrations. The results show that A. pseudogonyaulax has become a prominent member of the Alexandrium spp. community over the past decade in the study area. Analyses of long term monitoring data from the Limfjord confirmed a recent shift to A. pseudogonyaulax dominance. Cyst and toxin records of the species in Kiel Bight suggest a spreading potential into the brackish Baltic Sea, which might lead to an expansion of blooms under future climate conditions.

Diverse expression regulation of Hsp70 genes in scallops after exposure to toxic Alexandrium dinoflagellates

Heat shock proteins 70KD (Hsp70s) are highly conserved molecular chaperones with essential roles against biotic and abiotic stressors. Marine bivalves inhabit highly complex environments and could accumulate paralytic shellfish toxins (PSTs), the well-noted neurotoxins generated during harmful algal blooms. Here, we systematically analyzed Hsp70 genes (CfHsp70s) in Zhikong scallop (Chlamys farreri), an important aquaculture mollusk in China. Sixty-five CfHsp70s from eight sub-families were identified, and 47 of these genes showed expansion in the Hspa12 sub-family. After exposure to different PST-producing dinoflagellates, Alexandrium minutum and Alexandrium catenella, diverse CfHsp70s regulation presented in scallop hepatopancreas, mainly accumulating incoming PSTs, and kidneys, transforming PSTs into higher toxic analogs. All the up-regulated CfHsp70s were from CfHsp70B2, CfHspa12, and CfHspa5 sub-families. CfHsp70B2 sub-family was mainly induced in the hepatopancreas, and CfHspa12 sub-family was highly induced in the kidneys. CfHsp70s up-regulation under two dinoflagellates exposure was stronger in the kidneys (log₂FC: 19.5 and 18.6) than that in hepatopancreas (log₂FC: 4.3 and 6.1). Exposure to different Alexandrium species had varying effects, that in hepatopancreas, CfHsp70B2s were chronically induced only after A. catenella exposure, whereas in kidney, CfHspa12s were more acutely induced after exposure of A. minutum than A. caenella. Moreover, in Yesso scallops (Patinopecten yessoensis), only Hspa12s were up-regulated in hepatopancreas after A. catenella exposure, and all the Hsp70B2s were down-regulated. These organ-, toxin-, and species-dependent Hsp70 regulation suggested the functional diversity of duplicated Hsp70s in response to the stress by PST-producing algae. Our findings provide insights into the evolution and functional characteristics of Hsp70s in scallops.

Paralytic shellfish toxins, including deoxydecarbamoyl-STX, in wild-caught Tasmanian abalone (Haliotis rubra)

For the first time wild-caught Tasmanian abalone, Haliotis rubra, have been reported to contain paralytic shellfish toxins (PSTs). This observation followed blooms of the toxic dinoflagellate Gymnodinium catenatum. No illnesses were reported, but harvesting restrictions were enforced in commercial areas. Abalone were assayed using HPLC-FLD methodology based on AOAC official method 2005.06. An uncommon congener, deoxydecarbamoyl-STX (doSTX), was observed in addition to regulated PSTs as unassigned chromatographic peaks. A quantitative reference material was prepared from contaminated Tasmanian abalone viscera and ampouled at 54.2 μmol/L. The LD50 of doSTX via intraperitoneal injection was 1069 nmol/kg (95% confidence limits 983-1100 nmol/kg), indicating it is nearly 40 times less toxic than STX. A toxicity equivalence factor of 0.042 was generated using the mouse bioassay. Levels of PSTs varied among individuals from the same site, although the toxin profile remained relatively consistent. In the foot tissue, STX, decarbamoyl-STX and doSTX were identified. On a molar basis doSTX was the dominant congener in both foot and viscera samples. The viscera toxin profile was more complex, with other less toxic PST congeners observed and was similar to mussels from the same site. This finding implicates localised dinoflagellate blooms as the PST source in Tasmanian abalone.

Paralytic shellfish toxin profiles in mussel, cockle and razor shell under post-bloom natural conditions: Evidence of higher biotransformation in razor shells and cockles

Concentrations of the paralytic shellfish toxins GTX6, C1+2, GTX5, C3+4, dcSTX, dcNEO and dcGTX2+3 were determined by LC-FLD in composite samples of whole soft tissues of mussels (Mytilus galloprovincialis), cockles (Cerastoderma edule) and razor shells (Solen marginatus) after exposure to a Gymnodinium catenatum bloom. Specimens were harvested weekly during three months under natural depuration conditions in the Mira branch of Aveiro lagoon, Portugal. Under the decline of G. catenatum cell densities, elimination or transformation of the uptake toxins associated with the ingestion of toxic cells differed among the surveyed species. Ratio between the toxins dcSTX plus dcGTX2+3 plus dcNEO and toxins GTX6 plus GTX5 plus C1+2 plus C3+4 was used to illustrate the biotransformation occurring in the bivalves. Enhancement of the ratios was observed for razor shells and cockles seven weeks after the peak of the algal bloom. Most likely it reflects more intense biotransformation in razor shells and cockles than in mussels. Conversion into toxins of higher toxicity may prolong the bivalve toxicity. These results show the complexity of toxin elimination in bivalves under post-bloom conditions and emphasize the pertinence of monitoring programs of bivalve toxicity in order to protect human health.

Oyster transcriptome response to Alexandrium exposure is related to saxitoxin load and characterized by disrupted digestion, energy balance, and calcium and sodium signaling

Harmful Algal Blooms are worldwide occurrences that can cause poisoning in human seafood consumers as well as mortality and sublethal effets in wildlife, propagating economic losses. One of the most widespread toxigenic microalgal taxa is the dinoflagellate Genus Alexandrium, that includes species producing neurotoxins referred to as PST (Paralytic Shellfish Toxins). Blooms cause shellfish harvest restrictions to protect human consumers from accumulated toxins. Large inter-individual variability in toxin load within an exposed bivalve population complicates monitoring of shellfish toxicity for ecology and human health regulation. To decipher the physiological pathways involved in the bivalve response to PST, we explored the whole transcriptome of the digestive gland of the Pacific oyster Crassostrea gigas fed experimentally with a toxic Alexandrium minutum culture. The largest differences in transcript abundance were between oysters with contrasting toxin loads (1098 transcripts), rather than between exposed and non-exposed oysters (16 transcripts), emphasizing the importance of toxin load in oyster response to toxic dinoflagellates. Additionally, penalized regressions, innovative in this field, modeled accurately toxin load based upon only 70 transcripts. Transcriptomic differences between oysters with contrasting PST burdens revealed a limited suite of metabolic pathways affected, including ion channels, neuromuscular communication, and digestion, all of which are interconnected and linked to sodium and calcium exchanges. Carbohydrate metabolism, unconsidered previously in studies of harmful algal effects on shellfish, was also highlighted, suggesting energy challenge in oysters with high toxin loads. Associations between toxin load, genotype, and mRNA levels were revealed that open new doors for genetic studies identifying genetically-based low toxin accumulation.

Effect of CO2 on growth and toxicity of Alexandrium tamarense from the East China Sea, a major producer of paralytic shellfish toxins

In recent decades, the frequency and intensity of harmful algal blooms (HABs), as well as a profusion of toxic phytoplankton species, have significantly increased in coastal regions of China. Researchers attribute this to environmental changes such as rising atmospheric CO₂ levels. Such addition of carbon into the ocean ecosystem can lead to increased growth, enhanced metabolism, and altered toxicity of toxic phytoplankton communities resulting in serious human health concerns. In this study, the effects of elevated partial pressure of CO₂ (pCO₂) on the growth and toxicity of a strain of Alexandrium tamarense (ATDH) widespread in the East and South China Seas were investigated. Results of these studies showed a higher specific growth rate (0.31±0.05day^-1) when exposed to 1000μatm CO₂, (experimental), with a corresponding density of (2.02±0.19)×10⁷cellsL^-1, that was significantly larger than cells under 395μatm CO₂₍control). These data also revealed that elevated pCO₂ primarily affected the photosynthetic properties of cells in the exponential growth phase. Interestingly, measurement of the total toxin content per cell was reduced by half under elevated CO₂ conditions. The following individual toxins were measured in this study: C1, C2, GTX1, GTX2, GTX3, GTX4, GTX5, STX, dcGTX2, dcGTX3, and dcSTX. Cells grown in 1000μatm CO₂ showed an overall decrease in the cellular concentrations of C1, C2, GTX2, GTX3, GTX5, STX, dcGTX2, dcGTX3, and dcSTX, but an increase in GTX1 and GTX4. Total cellular toxicity per cell was measured revealing an increase of nearly 60% toxicity in the presence of elevated CO₂ compared to controls. This unusual result was attributed to a significant increase in the cellular concentrations of the more toxic derivatives, GTX1 and GTX4.Taken together; these findings indicate that the A. tamarense strain ATDH isolated from the East China Sea significantly increased in growth and cellular toxicity under elevated pCO₂ levels. These data may provide vital information regarding future HABs and the corresponding harmful effects as a result of increasing atmospheric CO₂.

Bioactive compounds of marine dinoflagellate isolates from western Greenland and their phylogenetic association within the genus Alexandrium

The diversity and biogeography of populations of the toxigenic marine dinoflagellate genus Alexandrium, a major global cause of paralytic shellfish poisoning (PSP), are represented by only a few studies based upon a low number of cultured isolates and remain poorly described in Arctic and sub-Arctic waters. Multiple clonal isolates (n=22) of the Alexandrium tamarense species complex, and a single isolate of A. tamutum, were collected from the water column while on board an oceanographic expedition to the west coast of Greenland. After culturing of these isolates under controlled conditions, their phylogenetic affinities within the genus Alexandrium were characterized by sequence analysis of nuclear large sub-unit (LSU) rDNA. Based upon morphological and molecular genetic criteria, all isolates of the A. tamarense species complex were consistent with membership in the Group I ribotype (previously known as the North American ribotype). Phenotypic signatures were also analyzed based upon their respective profiles of paralytic shellfish toxins (PST) and allelochemical interactions against a target cryptophyte Rhodomonas, as determined by lytic potency. All isolates conforming to the A. tamarense Group I produced PST, but no toxins were detected in A. tamutum P2E2. Unusually, only carbamoyl toxins were produced among the A. tamarense Group I isolates from Greenland; sulfocarbamoyl derivatives, generally present in A. tamarense population from other locations, including the Arctic, North Pacific and North Atlantic, were absent from all isolates. Allelochemical activity, causing cell lysis of Rhodomonas, but generally being unrelated to cellular PST, was expressed by all A. tamarense isolates and also by A. tamutum, but varied widely in potency. Comparison of the genotypic (rDNA) and phenotypic (PST profile, allelochemical activity) characteristics of Greenland isolates with those of other Arctic populations reveals a complex pattern of intra-specific diversity. Estimation of diversity relationships is problematic because of the distinct patterns of divergence and lack of evidence of linkage among the alternative biomarkers and morphology. Nevertheless, such studies are necessary as the basis for constructing hindcasting scenarios and predicting changes in Alexandrium species distribution in the Arctic from the regional to the global scale.

The effects of two sized polystyrene nanoplastics on the growth, physiological functions, and toxin production of Alexandrium tamarense

Micro- and nano-plastics (MNPs) are increasingly prevalent pollutants in marine ecosystems and result in various deleterious effects on marine organisms. There have been studies evaluated the toxic effects of MNPs on marine microalgae, but few of them focused on the effects of MNPs on dinoflagellate species and their toxins production, which could have significant implications on human health and ecological safety in coastal areas. In this study, the common harmful algal blooms-causing dinoflagellate Alexandrium tamarense was exposed to 0.1 and 1 μm sized polystyrene nanoplastics (NPs) to investigate the responding patterns of population growth, multiple physiological functions, as well as the intracellular paralytic shellfish toxins (PSTs) productions. The results indicated the population growth, photosynthetic parameters, nutrients (nitrate and phosphate) uptake rates and extracellular carbonic anhydrase activities (CA_ext) were all inhibited by the two sized NPs, accompanied by the prolonged and more aggregated microalgal cells under the observation of scanning electron microscope (SEM), and the inhibition effects were more severe under 1 μm sized NPs than 0.1 μm sized NPs. Finally, we found the intracellular PSTs contents increased 73.59% exposed to 0.1 μm sized NPs while decreased 85.50% exposed to 1 μm sized NPs comparing the controls at 96 h, without significant changes of relative compositions. These results provided evidence that MNPs were toxic to A. tamarense and affected their intracellular PSTs productions within 96 h, which is critical to consider when evaluating the potential risks of MNPs in marine ecosystems.

Alexandrium pacificum and Alexandrium minutum: Harmful or environmentally friendly?

Alexandrium minutum and Alexandrium pacificum are representatives of the dinoflagellate genus that regularly proliferate on the French coasts and other global coastlines. These harmful species may threaten shellfish harvest and human health due to their ability to synthesize neurotoxic alkaloids of the saxitoxin group. However, some dinoflagellates such as A. minutum, and as reported here A. pacificum as well, may also have a beneficial impact on the environment by producing dimethylsulfoniopropionate-DMSP, the precursor of dimethylsulfur-DMS and sulfate aerosols involved in climate balance. However, environmental conditions might influence Alexandrium physiology towards the production of harmful or environmentally friendly compounds. After assessing the influence of two salinity regimes (33 and 38) relative to each species origin (Atlantic French coast and Mediterranean Lagoon respectively), it appears that DMSP and toxin content was variable between the three experimented strains and that higher salinity disadvantages toxin production and tends to favor the production of the osmolytes DMSP and glycine betaine. Hence, this key metabolite production is strain and species-dependent and is influenced by environmental conditions of salinity which in turn, can diversely affect the environment. Widespread coastal blooms of A. minutum and A. pacificum, although being a risk for seafood contamination with toxins, are also a DMSP and DMS source that potentially contribute to the ecosystem structuration and climate. Regarding recent advances in DMSP biosynthesis pathway, 3 dsyB homologs were found in A. minutum but no homolog of the diatom sequence TpMMT.

Application of activated carbon to accelerate detoxification of paralytic shellfish toxins from mussels Mytilus galloprovincialis and scallops Chlamys farreri

Contamination of economic bivalves with paralytic shellfish toxins (PST) occurs frequently in many parts of the world, which potentially threatens consumer health and the marine aquaculture economy. It is the objective of this study to develop a suitable technology for accelerating detoxification of PST from shellfish using activated carbon (AC). The adsorption efficiency of PST by eight different AC materials and by different particle sizes of wood-based AC (WAC) were tested and compared. Then WAC particles (37-48µm) were fed to mussels Mytilus galloprovincialis and scallops Chlamys farreri previously contaminated with PST through feeding with dinoflagellate Alexandrium tamarense ATHK. Results showed that the maximum adsorption ratio (65%) of PST was obtained by WAC. No significant differences in adsorption ratios were found between different particle sizes of WAC. The toxicity of mussels decreased by 41% and 68% after detoxification with WAC for 1 d and 3 d, respectively. Meanwhile, the detoxification ratio of mussels was approximately 3 times higher than that of scallops. This study suggests that the WAC could be used to accelerate the detoxification of PST by shellfish.

Spatiotemporal variation of paralytic shellfish toxins in the sea area adjacent to the Changjiang River estuary

The Changjiang (Yangtze River) River estuary (CRE) and its adjacent coastal waters is a notable region for nutrient pollution, which results in severe problems of coastal eutrophication and harmful algal blooms (HABs). The occurrence of HABs, particularly those of dinoflagellate Alexandrium spp. capable of producing paralytic shellfish toxins (PSTs), has an increasing risk of contaminating seafood and poisoning human-beings. The investigation of PSTs, however, is often hampered by the relatively low abundance of Alexandrium spp. present in seawater. In this study, a monitoring strategy of PSTs using net-concentrated phytoplankton from a large volume of seawater was employed to examine spatiotemporal variations of PSTs in the CRE and its adjacent waters every month from February to September in 2015. Toxins in concentrated phytoplankton samples were analyzed using high-performance liquid chromatography coupled with a fluorescence detector (HPLC-FLD). The results showed that PSTs could be detected in phytoplankton samples during the sampling stage in the CRE and its adjacent waters. Toxin content increased gradually from February to May, reached the peak in June, and then decreased rapidly from July to September. The maximum value of PST content was 215 nmol m^-3 in June. Low-potency toxins N-sulfocarbamoyl toxins 1/2 (C1/2) were the most dominant components of PST in phytoplankton samples from February to June in 2015, while high-potency gonyautoxin 4 (GTX4) became the dominant component from July to September. Toxins were mainly detected from three regions, the sea area north to the CRE, the sea area east to the CRE, and sea area near Zhoushan Island south to the CRE. Based on the results of this study, it can be inferred that the three regions around the CRE in May and June is of high risk for PST contamination and seafood poisoning.

Changes of paralytic shellfish toxins in gills and digestive glands of the cockle Cerastoderma edule under post-bloom natural conditions

Concentrations of the paralytic shellfish toxins C1+2, C3+4, GTX5, GTX6, dcGTX2+3, dcSTX, dcNEO, GTX2+3, GTX1+4, STX and NEO were determined by LC-FLD in composite samples of digestive glands and gills of Cerastoderma edule cockle. The specimens were sampled in Aveiro lagoon, Portugal, under natural depuration conditions (days 0, 8, 12, 14, 19, 21 and 25) after exposure to a bloom of Gymnodinium catenatum. Individual paralytic shellfish toxins indicated different pathways of elimination and biotransformation in digestive gland and gills. Toxin concentrations in gills were lower than in digestive gland. Most of the quantified toxins in digestive gland decreased during the 25 days of observation according to negative exponential curves, and only GTX5, GTX6 and NEO showed slight irregularities with time. Concentrations of C1+2, C3+4 and dcGTX2+3 in gills decreased progressively, however GTX5, GTX6 and dcSTX showed pronounced increases. Higher concentrations of those toxins in days 8 and 12 in comparison to the initial value (day 0) indicate conversion of other toxins into GTX5, GTX6 and dcSTX during those periods. It appears that inter-conversion of toxins occurs as G. catenatum cells are retained in gills before being transferred to other compartments.