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The mixotrophic dinoflagellate Akashiwo sanguinea is known to have acute toxic effects on multiple marine organisms, while the composition and chemical properties of its toxins remain unclear. In this study, we established a method for separation and purification of A. sanguinea toxins using chromatographic techniques. The acetone extract of A. sanguinea exhibited higher hemolytic activity and shorter incubation time compared to methanol and ethyl acetate extracts. Five fractions were obtained by solid-phase extraction (SPE), of which SPE3 (acetone/water ratio 3:2) and SPE4 (acetone/water ratio 4:1) exhibited the highest hemolytic activities and allelopathic effects. Further purification on SPE3 and SPE4 using reverse-phase high-performance liquid chromatography (RP-HPLC) coupled with a diode array detector (DAD) resulted in 11 subfractions, among which Fr4-5 displayed the strongest hemolytic activity. Nearly all active subfractions exhibited higher hemolytic activities incubated under light than those in the dark (p < 0.05), suggesting that A. sanguinea can produce both photosensitive and non-photosensitive toxins, with the former being the primary contributors to its hemolytic activity. Molecular characterization by UV-Vis, FTIR, and HRMS/MS analysis revealed that the structural features of Fr4-5 were highly consistent with porphyrin analogs and could be derived from chlorophyll c-related precursors. These findings highlight that the photosensitive toxins in A. sanguinea may serve dual roles in stress adaptation and ecological competition, potentially contributing to the formation of the blooms.

Paralytic shellfish poisoning toxins (PSPTs) are a class of neurotoxins most known for causing illness from consuming contaminated shellfish. These toxins are also present in freshwater systems with the concern that they contaminate drinking and recreational waters. This review provides (1) a complete list of the 84+ known PSPTs and important chemical features; (2) a complete list of all environmental freshwater PSPT detections; (3) an outline of the certified PSPT methods and their inherent weaknesses; and (4) a discussion of PSPT toxicology, the weaknesses in existing data, and existing freshwater regulatory limits. We show ample evidence of production of freshwater PSPTs by cyanobacteria worldwide, but data and method uncertainties limit a proper risk assessment. One impediment is the poor understanding of freshwater PSPT profiles and lack of commercially available standards needed to identify and quantify freshwater PSPTs. Further constraints are the limitations of toxicological data derived from human and animal model exposures. Unassessed mouse toxicity data from 1978 allowed us to calculate and propose toxicity equivalency factors (TEF) for 11-hydroxysaxitoxin (11-OH STX; M2) and 11-OH dcSTX (dcM2). TEFs for the 11-OH STX epimers were calculated to be 0.4 and 0.6 for 11α-OH STX (M2α) and 11β-OH STX (M2β), while we estimate that TEFs for 11α-OH dcSTX (dcM2α) and 11β-OH dcSTX (dcM2β) congeners would be 0.16 and 0.23, respectively. Future needs for freshwater PSPTs include increasing the number of reference materials for environmental detection and toxicity evaluation, developing a better understanding of PSPT profiles and important environmental drivers, incorporating safety factors into exposure guidelines, and evaluating the accuracy of the established no-observed-adverse-effect level.

The marine environment emerges as a key provider of food and sustainable products. However, these benefits are accompanied by numerous challenges owing to harmful algal blooms (HAB) and their associated biotoxins, which accumulate in organisms, like bivalves, threatening seafood quality. Among the various biotoxins, paralytic shellfish toxins (PST), the causative agents of paralytic shellfish poisoning (PSP), are among the most potent, lethal, and frequently reported instances of human intoxication. Removing PST from marine system is particularly challenging because of their hydrophilicity, susceptibility to biotransformation and the potential influence of other substances naturally present in the environment. Although there are several methods applied to mitigate HAB, to the best of our knowledge there are no proven effective methods for removing PST in marine environments. Consequently, there is a need to develop efficient removal technologies, especially envisaging fast, environmentally safe, inexpensive, and readily available solutions. Having examined several proposed methods for removing PST (e.g., thermal and industrial procedures, adsorption using different materials, photodegradation, AOPs) and comparing their efficacy, this study aims to streamline the current knowledge on PST removal, identify knowledge gaps, and provide valuable insights for researchers, environmental managers, and policymakers engaged in mitigating the risks associated with PST.

The marine dinoflagellate Gymnodinium catenatum has been associated with paralytic shellfish poisoning (PSP) outbreaks in Portuguese waters for many years. PSP syndrome is caused by consumption of seafood contaminated with paralytic shellfish toxins (PSTs), a suite of potent neurotoxins. Gymnodinium catenatum was frequently reported along the Portuguese coast throughout the late 1980s and early 1990s, but was absent between 1995 and 2005. Since this time, G. catenatum blooms have been recurrent, causing contamination of fishery resources along the Atlantic coast of Portugal. The aim of this study was to evaluate the toxin profile of G. catenatum isolated from the Portuguese coast before and after the 10-year hiatus to determine changes and potential impacts for the region. Hydrophilic interaction liquid chromatography tandem mass spectrometry (HILIC-MS/MS) was utilized to determine the presence of any known and emerging PSTs in sample extracts. Several PST derivatives were identified, including the N-sulfocarbamoyl analogues (C1-4), gonyautoxin 5 (GTX5), gonyautoxin 6 (GTX6), and decarbamoyl derivatives, decarbamoyl saxitoxin (dcSTX), decarbamoyl neosaxitoxin (dcNeo) and decarbamoyl gonyautoxin 3 (dcGTX3). In addition, three known hydroxy benzoate derivatives, G. catenatum toxin 1 (GC1), GC2 and GC3, were confirmed in cultured and wild strains of G. catenatum. Moreover, two presumed N-hydroxylated analogues of GC2 and GC3, designated GC5 and GC6, are reported. This work contributes to our understanding of the toxigenicity of G. catenatum in the coastal waters of Portugal and provides valuable information on emerging PST classes that may be relevant for routine monitoring programs tasked with the prevention and control of marine toxins in fish and shellfish.

Marine algal toxins have garnered significant attention in the research community for their unique biochemical properties and potential medical applications. These bioactive compounds, produced by microalgae, pose significant risks due to their high toxicity, yet offer promising therapeutic benefits. Despite extensive research identifying over 300 marine algal toxins, including azaspiracids, brevetoxins, cyclic imines, and yessotoxins, gaps remain in the understanding of their pharmacological potential. In this paper, we critically review the classification, bioactive components, toxicology, pharmacological activities, and mechanisms of these toxins, with a particular focus on their clinical applications. Our motivation stems from the increasing interest in marine algal toxins as candidates for drug development, driven by their high specificity and affinity for various biological receptors. We aim to bridge the gap between toxicological research and therapeutic application, offering insights into the advantages and limitations of these compounds in comparison to other bioactive substances. This review not only enhances the understanding of marine algal toxins’ complexity and diversity, but also highlights their extensive application potential in medicine and bioscience, providing a foundation for future research and development in this field.

Several species of crabs from the Xanthidae family are recognized as dangerous marine organisms due to their potent neurotoxins, including paralytic shellfish toxin (PST), tetrodotoxin (TTX), and palytoxin (PLTX). However, the mechanisms of toxin accumulation and transport and the origin of these toxins in toxic xanthid crabs remain unknown. The identification of toxic crab species, their toxicity and toxin composition, and toxin profiles have been studied thus far. To date, more than ten species of xanthid crabs have been confirmed to possess toxins. Recently, several new studies on crabs, including the geographic distribution of toxin profiles and the ecological role of crabs, have been reported. Therefore, this review provides a summary of global research on toxic xanthid crabs, containing new findings and hypotheses on the toxification in and the origins of these crabs. Furthermore, the challenges and future perspectives in this field are also discussed.

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.

It is held as a paradigm that ribosomally synthesized peptides and proteins contain only L-amino acids. We demonstrate a ribosomal origin of the marine sponge—derived polytheonamides, exceptionally potent, giant natural-product toxins. Isolation of the biosynthetic genes from the sponge metagenome revealed a bacterial gene architecture. Only six candidate enzymes were identified for 48 posttrarelational modifications, including 18 epimerizations and 17 methylations of nonactivated carbon centers. Three enzymes were functionally validated, which showed that a radical S-adenosylmethionine enzyme is responsible for the unidirectional epimerization of multiple and different amino acids. Collectively, these complex alterations create toxins that function as unimolecular minimalistic ion channels with near-femtomolar activity. This study broadens the biosynthetic scope of ribosomal systems and creates new opportunities for peptide and protein bioengineering.

Sea anemones produce venoms of exceptional molecular diversity, with at least 17 different molecular scaffolds reported to date. These venom components have traditionally been classified according to pharmacological activity and amino acid sequence. However, this classification system suffers from vulnerabilities due to functional convergence and functional promiscuity. Furthermore, for most known sea anemone toxins, the exact receptors they target are either unknown, or at best incomplete. In this review, we first provide an overview of the sea anemone venom system and then focus on the venom components. We have organised the venom components by distinguishing firstly between proteins and non-proteinaceous compounds, secondly between enzymes and other proteins without enzymatic activity, then according to the structural scaffold, and finally according to molecular target.

Blooms of cyanobacteria have been documented throughout history, all over the world. Mass populations of these organisms typically present hazards to human health and are known for the production of a wide range of highly toxic metabolites—cyanotoxins, of which among the most common and most investigated are the microcystins. The toxicity of the family of microcystin congeners to animal and cell models has received much attention; however, less is known about their negative effects on human health, whether via acute or chronic exposure. Useful information may be acquired through epidemiological studies since they can contribute to knowledge of the relationships between cyanotoxins and human health in environmental settings. The aim of this review is to compile and evaluate the available published reports and epidemiological investigations of human health incidents associated with exposure to mass populations of cyanobacteria from throughout the world and to identify the occurrence and likely role of microcystins in these events. After an initial screening of 134 publications, 42 publications (25 on the chronic and 17 on the acute effects of cyanotoxins) describing 33 cases of poisonings by cyanobacterial toxins in 11 countries were reviewed. The countries were Australia, China, Sri Lanka, Namibia, Serbia, Sweden, UK, Portugal, Brazil, USA, and Canada. At least 36 publications link cyanobacteria/cyanotoxins including microcystins to adverse human health effects. The studies were published between 1960 and 2016. Although the scattered epidemiological evidence does not provide a definitive conclusion, it can serve as additional information for the medical assessment of the role of microcystins in cancer development and other human health problems. This paper discusses the major cases of cyanotoxin poisonings as well as the strengths, weaknesses, and importance of the performed epidemiological research. This study also proposes some recommendations for future epidemiological work.