Development of a LC-MS/MS method for the quantification of goniodomins A and B and its application to Alexandrium pseudogonyaulax strains and plankton field samples of Danish coastal waters

Did algal toxin and Klebsiella infections cause the unexplained 2007 mass mortality event in Danish and Swedish marine mammals?

An unusual mass mortality event (MME) of harbour seals (Phoca vitulina) and harbour porpoises (Phocoena phocoena) occurred in Denmark and Sweden in June 2007. Prior to this incident, the region had experienced two MMEs in harbour seals caused by Phocine Distemper Virus (PDV) in 1988 and 2002. Although epidemiology and symptoms of the 2007 MME resembled PDV, none of the animals examined for PDV tested positive. Thus, it has been speculated that another - yet unknown - pathogen caused the June 2007 MME. To shed new light on the likely cause of death, we combine previously unpublished veterinary examinations of harbour seals with novel analyses of algal toxins and algal monitoring data. All harbour seals subject to pathological examination showed pneumonia, but were negative for PDV, influenza and coronavirus. Histological analyses revealed septicaemia in multiple animals, and six animals tested positive for Klebsiella pneumonia. Furthermore, we detected the algal Dinophysis toxin DTX-1b (1-115 ng g-1) in five seals subject to toxicology, representing the first time DTX-1b has been detected in marine vertebrates. However, no animals tested positive for both Klebsiella and toxins. Thus, while our relatively small sample size prevent firm conclusions on causative agents, we speculate that the unexplained MME may have been caused by a chance incidence of multiple pathogens acting in parallel in June 2007, including Dinophysis toxin and Klebsiella. Our study illustrates the complexity of wildlife MMEs and highlights the need for thorough sampling during and after MMEs, as well as additional research on and monitoring of DTX-1b and other algal toxins in the region.

Thecal plate morphology, molecular phylogeny, and toxin analyses reveal two novel species of Alexandrium (Dinophyceae) and their potential for toxin production

This study describes two novel species of marine dinophytes in the genus Alexandrium. Morphological characteristics and phylogenetic analyses support the placement of the new taxa, herein designated as Alexandrium limii sp. nov. and A. ogatae sp. nov. Alexandrium limii, a species closely related to A. taylorii, is distinguished by having a shorter 2'/4' suture length, narrower plates 1' and 6'', with larger length: width ratios, and by the position of the ventral pore (Vp). Alexandrium ogatae is distinguishable with its metasert plate 1' having almost parallel lateral margins, and by lacking a Vp. Production of paralytic shellfish toxins (PSTs), cycloimines, and goniodomins (GDs) in clonal cultures of A. ogatae, A. limii, and A. taylorii were examined analytically and the results showed that all strains contained GDs, with GDA as major variants (6-14 pg cell-1) for all strains except the Japanese strain of A. limii, which exclusively had a desmethyl variant of GDA (1.4-7.3 pg cell-1). None of the strains contained detectable levels of PSTs and cycloimines.

Mass spectrometric characterization of the seco acid formed by cleavage of the macrolide ring of the algal metabolite goniodomin A

Goniodomin A (GDA) is a polyketide macrolide produced by multiple species of the marine dinoflagellate genus Alexandrium. GDA is unusual in that it undergoes cleavage of the ester linkage under mild conditions to give mixtures of seco acids (GDA-sa). Ring-opening occurs even in pure water although the rate of cleavage accelerates with increasing pH. The seco acids exist as a dynamic mixture of structural and stereo isomers which is only partially separable by chromatography. Freshly prepared seco acids show only end absorption in the UV spectrum but a gradual bathochromic change occurs, which is consistent with formation of α,β-unsaturated ketones. Use of NMR and crystallography is precluded for structure elucidation. Nevertheless, structural assignments can be made by mass spectrometric techniques. Retro-Diels-Alder fragmentation has been of value for independently characterizing the head and tail regions of the seco acids. The chemical transformations of GDA revealed in the current studies help clarify observations made on laboratory cultures and in the natural environment. GDA has been found to reside mainly within the algal cells while the seco acids are mainly external with the transformation of GDA to the seco acids occurring largely outside the cells. This relationship, plus the fact that GDA is short-lived in growth medium whereas GDA-sa is long-lived, suggests that the toxicological properties of GDA-sa in its natural environment are more important for the survival of the Alexandrium spp. than those of GDA. The structural similarity of GDA-sa to that of monensin is noted. Monensin has strong antimicrobial properties, attributed to its ability to transport sodium ions across cell membranes. We propose that toxic properties of GDA may primarily be due to the ability of GDA-sa to mediate metal ion transport across cell membranes of predator organisms.

First Identification of Amphidinols from Mexican Strains and New Analogs

The genus Amphidinium has been the subject of recent attention due to the production of polyketide metabolites. Some of these compounds have shown significant bioactivities and could be related to species interactions in the natural benthic microenvironment. Among these compounds, amphidinols (AMs) are suspected to be related to fish kills and probably implicated in ciguatera symptoms associated with the occurrence of benthic harmful algal blooms (bHABs). Here, we present the first report of a variety of AMs produced by cultured strains from several species from the Mexican Pacific, the Gulf of California, and the Gulf of Mexico. Through ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS), ten previously known AMs (AM02, -04, -05, -06, -07, -09, -11, -14, -15, and -17), four recently reported AMs (N7, N8/N9, N12, and N13), and three new variants (U1, U2, and U3) were identified. Of the twelve analyzed Amphidinium cultures, five were not AM producers, and the cell quotas of the remaining seven strains ranged from close to nondetectable to a maximum of 1694 fg cell-1, with many intermediate levels in between. The cultures from the Mexican North Pacific coast produced AMs in a higher quantity and variety than those from worldwide locations. This is the first study of AMs from Mexican Amphidinium strains, and our results confirm the relevance of continuing the investigation of the genus bioactive metabolites.

Apparent biogeographical trends in Alexandrium blooms for northern Europe: identifying links to climate change and effective adaptive actions

The marine dinoflagellate Alexandrium Halim represents perhaps the most significant and intensively studied genus with respect to species diversity, life history strategies, toxigenicity, biogeographical distribution, and global magnitude and consequences harmful algal blooms (HABs). The socioeconomic impacts, environmental and human health risks, and mitigation strategies for toxigenic Alexandrium blooms have also been explored in recent years. Human adaptive actions based on future scenarios of bloom dynamics and shifts in biogeographical distribution under climate-change parameters remain under development and not yet implemented on a regional scale. In the CoCliME (Co-development of climate services for adaptation to changing marine ecosystems) project these issues were addressed with respect to past, current and anticipated future status of key HAB genera and expected benefits of enhanced monitoring. Data on the distribution and frequency of Alexandrium blooms related to paralytic shellfish toxin (PST) events from key CoCliME Case Study areas, comprising the North Sea and adjacent Kattegat-Skagerrak, Norwegian Sea, and Baltic Sea, and eastern North Atlantic marginal seas, were evaluated in a contemporary and historical context over the past several decades. The first evidence of possible biogeographical expansion of Alexandrium taxa into eastern Arctic gateways was provided from DNA barcoding signatures. Various key climate change indicators, such as salinity, temperature, and water-column stratification, relevant to Alexandrium bloom initiation and development were identified. The possible influence of changing variables on bloom dynamics, magnitude, frequency and spatial and temporal distribution were interpreted in the context of regional ocean climate models. These climate change impact indicators may play key roles in selecting for the occurrence and diversity of Alexandrium species within the broader microeukaryote communities. For example, shifts to higher temperature and lower salinity regimes predicted for the southern North Sea indicate the potential for increased Alexandrium blooms, currently absent from this area. Ecological and socioeconomic impacts of Alexandrium blooms and effects on fisheries and aquaculture resources and coastal ecosystem function are evaluated, and, where feasible, effective adaptation strategies are proposed herein as emerging climate services.

New Knowledge on Distribution and Abundance of Toxic Microalgal Species and Related Toxins in the Northwestern Black Sea

Numerous potentially toxic plankton species commonly occur in the Black Sea, and phycotoxins have been reported. However, the taxonomy, phycotoxin profiles, and distribution of harmful microalgae in the basin are still understudied. An integrated microscopic (light microscopy) and molecular (18S rRNA gene metabarcoding and qPCR) approach complemented with toxin analysis was applied at 41 stations in the northwestern part of the Black Sea for better taxonomic coverage and toxin profiling in natural populations. The combined dataset included 20 potentially toxic species, some of which (Dinophysis acuminata, Dinophysis acuta, Gonyaulax spinifera, and Karlodinium veneficum) were detected in over 95% of the stations. In parallel, pectenotoxins (PTX-2 as a major toxin) were registered in all samples, and yessotoxins were present at most of the sampling points. PTX-1 and PTX-13, as well as some YTX variants, were recorded for the first time in the basin. A positive correlation was found between the cell abundance of Dinophysis acuta and pectenotoxins, and between Lingulodinium polyedra and Protoceratium reticulatum and yessotoxins. Toxic microalgae and toxin variant abundance and spatial distribution was associated with environmental parameters. Despite the low levels of the identified phycotoxins and their low oral toxicity, chronic toxic exposure could represent an ecosystem and human health hazard.

Increase in records of toxic phytoplankton and associated toxins in water samples in the Patagonian Shelf (Argentina) over 40 years of field surveys

Historical records (1980-2018) of potentially toxic phytoplankton and phycotoxins on the Argentine Continental Shelf (35°S-56.5°S) and adjacent ocean waters were systematically reviewed from scientific literature to assess their abundance and diversity over spatial and temporal scales. Records increased from 124 in the period 1980-1992 to 638 in 2006-2018, and the scanned area expanded from coastal to offshore waters including the shelf-break front. Alexandrium was the most reported genus (54%) during 1980-1992 and Pseudo-nitzschia (52%) during 1993-2005. By 2006-2018, a higher diversity was documented: Alexandrium (20%), Dinophysis (32%), Pseudo-nitzschia (31%), and the most recently described potentially toxic dinoflagellates of the family Amphidomataceae (8%). Likewise, a wider spectrum of phycotoxins was documented in the last decade, with lipophilic (LSTs) and paralytic shellfish toxins (PSTs) as the most recorded. Increased records are related to intensified monitoring, more detailed taxonomic analyses and more sensitive chemical techniques for marine biotoxin detection. This quantitative assessment brings light to the widespread occurrence of HABs along contrasting areas of the Patagonian Shelf and sets the basis for ecosystem risk evaluation. Moreover, comparison of toxic phytoplankton reported in the SW Atlantic with those in similar temperate seas in the North Atlantic and the Pacific Ocean, disclose ocean basin differences in strain toxicity of A. ostenfeldii, D. tripos and Azadinium species.

Unknown Extracellular and Bioactive Metabolites of the Genus Alexandrium: A Review of Overlooked Toxins

Various species of Alexandrium can produce a number of bioactive compounds, e.g., paralytic shellfish toxins (PSTs), spirolides, gymnodimines, goniodomins, and also uncharacterised bioactive extracellular compounds (BECs). The latter metabolites are released into the environment and affect a large range of organisms (from protists to fishes and mammalian cell lines). These compounds mediate allelochemical interactions, have anti-grazing and anti-parasitic activities, and have a potentially strong structuring role for the dynamic of Alexandrium blooms. In many studies evaluating the effects of Alexandrium on marine organisms, only the classical toxins were reported and the involvement of BECs was not considered. A lack of information on the presence/absence of BECs in experimental strains is likely the cause of contrasting results in the literature that render impossible a distinction between PSTs and BECs effects. We review the knowledge on Alexandrium BEC, (i.e., producing species, target cells, physiological effects, detection methods and molecular candidates). Overall, we highlight the need to identify the nature of Alexandrium BECs and urge further research on the chemical interactions according to their ecological importance in the planktonic chemical warfare and due to their potential collateral damage to a wide range of organisms.

Paralytic Shellfish Poisoning (PSP) in Mussels from the Eastern Cantabrian Sea: Toxicity, Toxin Profile, and Co-Occurrence with Cyclic Imines

In the late autumn of 2018 and 2019, some samples taken by the official monitoring systems of Cantabria and the Basque Country were found to be paralytic shellfish poisoning (PSP)-positive using a mouse bioassay. To confirm the presence of PSP toxins and to obtain their profile, these samples were analyzed using an optimized version of the Official Method AOAC 2005.06 and using LC–MS/MS (HILIC). The presence of some PSP toxins (PSTs) in that geographical area (~600 km of coast) was confirmed for the first time. The estimated toxicities ranged from 170 to 983 µg STXdiHCl eq.·kg⁻¹ for the AOAC 2005.06 method and from 150 to 1094 µg STXdiHCl eq.·kg⁻¹ for the LC–MS/MS method, with a good correlation between both methods (r² = 0.94). Most samples contained STX, GTX2,3, and GTX1,4, and some also had NEO and dcGTX2. All of the PSP-positive samples also contained gymnodimine A, with the concentrations of the two groups of toxins being significantly correlated. The PSP toxin profiles suggest that a species of the genus Alexandrium was likely the causative agent. The presence of gymnodimine A suggests that A. ostenfeldii could be involved, but the contribution of a mixture of Alexandrium species cannot be ruled out.

Alkali Metal- and Acid-Catalyzed Interconversion of Goniodomin A with Congeners B and C

Goniodomin A (GDA, 1) is a phycotoxin produced by at least four species of Alexandrium dinoflagellates that are found globally in brackish estuaries and lagoons. It is a linear polyketide with six oxygen heterocyclic rings that is cyclized into a macrocyclic structure via lactone formation. Two of the oxygen heterocycles in 1 comprise a spiro-bis-pyran, whereas goniodomin B (GDB) contains a 2,7-dioxabicyclo[3.3.1]nonane ring system fused to a pyran. When H₂O is present, 1 undergoes facile conversion to isomer GDB and to an α,β-unsaturated ketone, goniodomin C (GDC, 7). GDB and GDC can be formed from GDA by cleavage of the spiro-bis-pyran ring system. GDA, but not GDB or GDC, forms a crown ether-type complex with K⁺. Equilibration of GDA with GDB and GDC is observed in the presence of H⁺ and of Na⁺, but the equilibrated mixtures revert to GDA upon addition of K⁺. Structural differences have been found between the K⁺ and Na⁺ complexes. The association of GDA with K⁺ is strong, while that with Na⁺ is weak. The K⁺ complex has a compact, well-defined structure, whereas Na⁺ complexes are an ill-defined mixture of species. Analyses of in vitro A. monilatum and A. hiranoi cultures indicate that only GDA is present in the cells; GDB and GDC appear to be postharvest transformation products.

Molecular Identification and Toxin Analysis of Alexandrium spp. in the Beibu Gulf: First Report of Toxic A. tamiyavanichii in Chinese Coastal Waters

The frequency of harmful algal blooms (HABs) has increased in China in recent years. Information about harmful dinoflagellates and paralytic shellfish toxins (PSTs) is still limited in China, especially in the Beibu Gulf, where PSTs in shellfish have exceeded food safety guidelines on multiple occasions. To explore the nature of the threat from PSTs in the region, eight Alexandrium strains were isolated from waters of the Beibu Gulf and examined using phylogenetic analyses of large subunit (LSU) rDNA, small subunit (SSU) rDNA, and internal transcribed spacer (ITS) sequences. Their toxin composition profiles were also determined using liquid chromatography-tandem mass spectrometry (LC-MS/MS). All eight strains clustered in the phylogenetic tree with A. pseudogonyaulax, A. affine, and A. tamiyavanichii from other locations, forming three well-resolved groups. The intraspecific genetic distances of the three Alexandrium species were significantly smaller than interspecific genetic distances for Alexandrium species. Beibu Gulf isolates were therefore classified as A. pseudogonyaulax, A. affine, and A. tamiyavanichii. No PSTs were identified in A. pseudogonyaulax, but low levels of gonyautoxins (GTXs) 1 to 5, and saxitoxin (STX) were detected in A. tamiyavanichii (a total of 4.60 fmol/cell). The extremely low level of toxicity is inconsistent with PST detection above regulatory levels on multiple occasions within the Beibu Gulf, suggesting that higher toxicity strains may occur in those waters, but were unsampled. Other explanations including biotransformation of PSTs in shellfish and the presence of other PST-producing algae are also suggested. Understanding the toxicity and phylogeny of Alexandrium species provides foundational data for the protection of public health in the Beibu Gulf region and the mitigation of HAB events.

Harmful algal blooms and their effects in coastal seas of Northern Europe

Harmful algal blooms (HAB) are recurrent phenomena in northern Europe along the coasts of the Baltic Sea, Kattegat-Skagerrak, eastern North Sea, Norwegian Sea and the Barents Sea. These HABs have caused occasional massive losses for the aquaculture industry and have chronically affected socioeconomic interests in several ways. This status review gives an overview of historical HAB events and summarises reports to the Harmful Algae Event Database from 1986 to the end of year 2019 and observations made in long term monitoring programmes of potentially harmful phytoplankton and of phycotoxins in bivalve shellfish. Major HAB taxa causing fish mortalities in the region include blooms of the prymnesiophyte Chrysochromulina leadbeateri in northern Norway in 1991 and 2019, resulting in huge economic losses for fish farmers. A bloom of the prymesiophyte Prymnesium polylepis (syn. Chrysochromulina polylepis) in the Kattegat-Skagerrak in 1988 was ecosystem disruptive. Blooms of the prymnesiophyte Phaeocystis spp. have caused accumulations of foam on beaches in the southwestern North Sea and Wadden Sea coasts and shellfish mortality has been linked to their occurrence. Mortality of shellfish linked to HAB events has been observed in estuarine waters associated with influx of water from the southern North Sea. The first bloom of the dictyochophyte genus Pseudochattonella was observed in 1998, and since then such blooms have been observed in high cell densities in spring causing fish mortalities some years. Dinoflagellates, primarily Dinophysis spp., intermittently yield concentrations of Diarrhetic Shellfish Toxins (DST) in blue mussels, Mytilus edulis, above regulatory limits along the coasts of Norway, Denmark and the Swedish west coast. On average, DST levels in shellfish have decreased along the Swedish and Norwegian Skagerrak coasts since approximately 2006, coinciding with a decrease in the cell abundance of D. acuta. Among dinoflagellates, Alexandrium species are the major source of Paralytic Shellfish Toxins (PST) in the region. PST concentrations above regulatory levels were rare in the Skagerrak-Kattegat during the three decadal review period, but frequent and often abundant findings of Alexandrium resting cysts in surface sediments indicate a high potential risk for blooms. PST levels often above regulatory limits along the west coast of Norway are associated with A. catenella (ribotype Group 1) as the main toxin producer. Other Alexandrium species, such as A. ostenfeldii and A. minutum, are capable of producing PST among some populations but are usually not associated with PSP events in the region. The cell abundance of A. pseudogonyaulax, a producer of the ichthyotoxin goniodomin (GD), has increased in the Skagerrak-Kattegat since 2010, and may constitute an emerging threat. The dinoflagellate Azadinium spp. have been unequivocally linked to the presence of azaspiracid toxins (AZT) responsible for Azaspiracid Shellfish Poisoning (AZP) in northern Europe. These toxins were detected in bivalve shellfish at concentrations above regulatory limits for the first time in Norway in blue mussels in 2005 and in Sweden in blue mussels and oysters (Ostrea edulis and Crassostrea gigas) in 2018. Certain members of the diatom genus Pseudo-nitzschia produce the neurotoxin domoic acid and analogs known as Amnesic Shellfish Toxins (AST). Blooms of Pseudo-nitzschia were common in the North Sea and the Skagerrak-Kattegat, but levels of AST in bivalve shellfish were rarely above regulatory limits during the review period. Summer cyanobacteria blooms in the Baltic Sea are a concern mainly for tourism by causing massive fouling of bathing water and beaches. Some of the cyanobacteria produce toxins, e.g. Nodularia spumigena, producer of nodularin, which may be a human health problem and cause occasional dog mortalities. Coastal and shelf sea regions in northern Europe provide a key supply of seafood, socioeconomic well-being and ecosystem services. Increasing anthropogenic influence and climate change create environmental stressors causing shifts in the biogeography and intensity of HABs. Continued monitoring of HAB and phycotoxins and the operation of historical databases such as HAEDAT provide not only an ongoing status report but also provide a way to interpret causes and mechanisms of HABs.

Revisiting the toxin profile of Alexandrium pseudogonyaulax; Formation of a desmethyl congener of goniodomin A

During a survey of the production of goniodomin A (GDA) by Alexandrium pseudogonyaulax in Danish coastal waters, Krock et al. (2018) obtained mass spectral evidence for the presence of a truncated congener, herein termed GD754, having a molecular weight 14 Da lower than GDA and assigned it as goniodomin B (GDB). An erroneous structure of GDB involving deletion of a methylene group between rings B and D had previously been reported by Espiña et al. (2016) but without experimental details. HPLC properties reported by Krock for GD754 point to it being a homolog of GDA. Comparison of mass spectral fragmentation data reported for GD754 with fragmentation data for GDA, show it to be a truncated form of GDA with the deletion involving a CH₂ group from ring F or one of the two methyl substituents on ring F, not elsewhere on the molecule. On biosynthetic grounds, the GD754 congener is proposed to be 34-desmethyl-GDA. Further experimental work will be required to confirm this hypothesis.

A Mediterranean Alexandrium taylorii (Dinophyceae) Strain Produces Goniodomin A and Lytic Compounds but Not Paralytic Shellfish Toxins

Species of the dinophyte genus Alexandrium are widely distributed and are notorious bloom formers and producers of various potent phycotoxins. The species Alexandrium taylorii is known to form recurrent and dense blooms in the Mediterranean, but its toxin production potential is poorly studied. Here we investigated toxin production potential of a Mediterranean A. taylorii clonal strain by combining state-of-the-art screening for various toxins known to be produced within Alexandrium with a sound morphological and molecular designation of the studied strain. As shown by a detailed thecal plate analysis, morphology of the A. taylorii strain AY7T from the Adriatic Sea conformed with the original species description. Moreover, newly obtained Large Subunit (LSU) and Internal Transcribed Spacers (ITS) rDNA sequences perfectly matched with the majority of other Mediterranean A. taylorii strains from the databases. Based on both ion pair chromatography coupled to post-column derivatization and fluorescence detection (LC-FLD) and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) analysis it is shown that A. taylorii AY7T does not produce paralytic shellfish toxins (PST) above a detection limit of ca. 1 fg cell-1, and also lacks any traces of spirolides and gymnodimines. The strain caused cell lysis of protistan species due to poorly characterized lytic compounds, with a density of 185 cells mL-1 causing 50% cell lysis of cryptophyte bioassay target cells (EC50). As shown here for the first time A. taylorii AY7T produced goniodomin A (GDA) at a cellular level of 11.7 pg cell-1. This first report of goniodomin (GD) production of A. taylorii supports the close evolutionary relationship of A. taylorii to other identified GD-producing Alexandrium species. As GD have been causatively linked to fish kills, future studies of Mediterranean A. taylorii blooms should include analysis of GD and should draw attention to potential links to fish kills or other environmental damage.

A Screening Tool for the Direct Analysis of Marine and Freshwater Phycotoxins in Organic SPATT Extracts from the Chesapeake Bay

Many detection methods for phycotoxins, bioactive compounds produced by harmful algae, focus on one compound or a class of related compounds. Multiple harmful algal species often co-occur in the environment, however, emphasizing the need to analyze for the presence of multiple groups of marine and freshwater phycotoxins in environmental samples, e.g., extracts from solid phase adsorption toxin tracking (SPATT). Two methods were developed to screen for 13 phycotoxins (microcystin-RR, -LR, -YR, azaspiracid-1, -2, karlotoxin 3, goniodomin A, brevetoxin-2, yessotoxin, pectenotoxin-2, dinophysistoxin-1, -2, and okadaic acid) in organic SPATT extracts using ultra-performance liquid chromatography–tandem mass spectrometry (UPLC-MS/MS) equipped with a trapping dimension (trap) and at-column dilution (ACD). The performance of each compound under 36 combinations of chromatographic conditions was characterized, and two final methods, acidic and basic, were selected based on peak shapes, signal intensities, resolution, and the separation in time of positive and negative MS ionization modes. Injection volumes of up to 1 mL were possible through trap/ACD technology, resulting in limits of detection between 0.001 and 0.05 µg/L across the analytes. Benefits highlighted in this study, beyond the improved detection limits and co-detection of multiple toxin groups, include the ability to inject samples of 100% organic solvent, ensuring analyte stability and streamlining workflow through the elimination of laborious sample preparation steps.

Algal Toxin Goniodomin A Binds Potassium Ion Selectively to Yield a Conformationally Altered Complex with Potential Biological Consequences

The marine toxin goniodomin A (GDA) is a polycyclic macrolide containing a spiroacetal and three cyclic ethers as part of the macrocycle backbone. GDA is produced by three species of the Alexandrium genus of dinoflagellates, blooms of which are associated with "red tides", which are widely dispersed and can cause significant harm to marine life. The toxicity of GDA has been attributed to stabilization of the filamentous form of the actin group of structural proteins, but the structural basis for its binding is not known. Japanese workers, capitalizing on the assumed rigidity of the heavily substituted macrolide ring, assigned the relative configuration and conformation by relying on NMR coupling constants and NOEs; the absolute configuration was assigned by degradation to a fragment that was compared with synthetic material. We have confirmed the absolute structure and broad features of the conformation by X-ray crystallography but have found GDA to complex with alkali metal ions in spite of two of the heterocyclic rings facing outward. Such an arrangement would have been expected to impair the ability of GDA to form a crown-ether-type multidentate complex. GDA shows preference for K⁺, Rb⁺, and Cs⁺ over Li⁺ and Na⁺ in determinations of relative affinities by TLC on metal-ion-impregnated silica gel plates and by electrospray mass spectrometry. NMR studies employing the K⁺ complex of GDA, formed from potassium tetrakis[pentafluorophenyl]borate (KBArF₂₀), reveal a major alteration of the conformation of the macrolide ring. These observations argue against the prior assumption of rigidity of the ring. Alterations in chemical shifts, coupling constants, and NOEs indicate the involvement of most of the molecule other than ring F. Molecular mechanics simulations suggest K⁺ forms a heptacoordinate complex involving O_A, O_B, O_C, O_D, O_E, and the C-26 and C-27 hydroxy groups. We speculate that complexation of K⁺ with GDA electrostatically stabilizes the complex of GDA with filamentous actin in marine animals due to the protein being negatively charged at physiological pH. GDA may also cause potassium leakage through cell membranes. This study provides insight into the structural features and chemistry of GDA that may be responsible for significant ecological damage associated with the GDA-producing algal blooms.

The toxin goniodomin, produced by Alexandrium spp., is identical to goniodomin A

In 1968 Burkholder and associates (J. Antibiot. (Tokyo)1968, 21, 659-664) isolated the antifungal toxin goniodomin from an unidentified Puerto Rican dinoflagellate and partially characterized its structure. Subsequently, a metabolite of Alexandrium hiranoi was isolated by Murakami et al. from a bloom in Japan and its structure was established (Tetrahedron Lett.1988, 29, 1149-1152). The Japanese substance had strong similarities to Burkholder's but due to uncertainty as to whether it was identical or only similar, Murakami named his toxin goniodomin A. A detailed study of this question now provides compelling evidence that Burkholder's goniodomin is identical to goniodomin A. Morphological characterization of the dinoflagellate suggests that it was the genus Alexandrium but insufficient evidence is available to make a definite identification of the species. This is the only report of goniodomin in the Caribbean region.

Ocean acidification increases domoic acid contents during a spring to summer succession of coastal phytoplankton

Enrichment of the oceans with CO₂ may be beneficial for some marine phytoplankton, including harmful algae. Numerous laboratory experiments provided valuable insights into the effects of elevated pCO₂ on the growth and physiology of harmful algal species, including the production of phycotoxins. Experiments close to natural conditions are the next step to improve predictions, as they consider the complex interplay between biotic and abiotic factors that can confound the direct effects of ocean acidification. We therefore investigated the effect of ocean acidification on the occurrence and abundance of phycotoxins in bulk plankton samples during a long-term mesocosm experiment in the Gullmar Fjord, Sweden, an area frequently experiencing harmful algal blooms. During the experimental period, a total of seven phycotoxin-producing harmful algal genera were identified in the fjord, and in accordance, six toxin classes were detected. However, within the mesocosms, only domoic acid and the corresponding producer Pseudo-nitzschia spp. was observed. Despite high variation within treatments, significantly higher particulate domoic acid contents were measured in the mesocosms with elevated pCO₂. Higher particulate domoic acid contents were additionally associated with macronutrient limitation. The risks associated with potentially higher phycotoxin levels in the future ocean warrants attention and should be considered in prospective monitoring strategies for coastal marine waters.

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.