Geographical distribution, molecular and toxin diversity of the dinoflagellate species Gambierdiscus honu in the Pacific region

Targeted and non-targeted mass spectrometry to explore the chemical diversity of the genus Gambierdiscus in the Atlantic Ocean

Dinoflagellates of the genus Gambierdiscus have been associated with ciguatera, the most common non-bacterial fish-related intoxication in the world. Many studies report the presence of potentially toxic Gambierdiscus species along the Atlantic coasts including G. australes, G. silvae and G. excentricus. Estimates of their toxicity, as determined by bio-assays, vary substantially, both between species and strains of the same species. Therefore, there is a need for additional knowledge on the metabolite production of Gambierdiscus species and their variation to better understand species differences. Using liquid chromatography coupled to mass spectrometry, toxin and metabolomic profiles of five species of Gambierdiscus found in the Atlantic Ocean were reported. In addition, a molecular network was constructed aiming at annotating the metabolomes. Results demonstrated that G. excentricus could be discriminated from the other species based solely on the presence of MTX4 and sulfo-gambierones and that the variation in toxin content for a single strain could be up to a factor of two due to different culture conditions between laboratories. While untargeted analyses highlighted a higher variability at the metabolome level, signal correction was applied and supervised multivariate statistics performed on the untargeted data set permitted the selection of 567 features potentially useful as biomarkers for the distinction of G. excentricus, G. caribaeus, G. carolinianus, G. silvae and G. belizeanus. Further studies will be required to validate the use of these biomarkers in discriminating Gambierdiscus species. The study also provided an overview about 17 compound classes present in Gambierdiscus, however, significant improvements in annotation are still required to reach a more comprehensive knowledge of Gambierdiscus' metabolome.

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

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

Ciguatera poisoning in French Polynesia: A review of the distribution and toxicity of Gambierdiscus spp., and related impacts on food web components and human health

Ciguatera Poisoning (CP) is a seafood poisoning highly prevalent in French Polynesia. This illness results from the consumption of seafood contaminated with ciguatoxins (CTXs) produced by Gambierdiscus, a benthic dinoflagellate. Ciguatera significantly degrades the health and economic well-being of local communities largely dependent on reef fisheries for their subsistence. French Polynesia has been the site of rich and active CP research since the 1960's. The environmental, toxicological, and epidemiological data obtained in the frame of large-scale field surveys and a country-wide CP case reporting program conducted over the past three decades in the five island groups of French Polynesia are reviewed. Results show toxin production in Gambierdiscus in the natural environment may vary considerably at a temporal and spatial scale, and that several locales clearly represent Gambierdiscus spp. "biodiversity hotspots". Current data also suggest the "hot" species G. polynesiensis could be the primary source of CTXs in local ciguateric biotopes, pending formal confirmation. The prevalence of ciguatoxic fish and the CTX levels observed in several locales were remarkably high, with herbivores and omnivores often as toxic as carnivores. Results also confirm the strong local influence of Gambierdiscus spp. on the CTX toxin profiles characterized across multiple food web components including in CP-prone marine invertebrates. The statistics, obtained in the frame of a long-term epidemiological surveillance program established in 2007, point towards an apparent decline in the number of CP cases in French Polynesia as a whole; however, incidence rates remain dangerously high in some islands. Several of the challenges and opportunities, most notably those linked to the strong cultural ramifications of CP among local communities, that need to be considered to define effective risk management strategies are addressed.

Concentration ciguatoxins in fillet of fish: A global systematic review and meta-analysis

In the current study, an attempt was made to meta-analyze and discuss the concentration of ciguatoxins (CTXs) in fillets of fish based on country and water resources subgroups. The search was conducted in Scopus and PubMed, Embase and Web of Science to retrieve papers about the concentration of CTXs in fillet fish until July 2022. Meta-analysis concentration of CTXs was conducted based on countries and water resources subgroups in the random effects model (REM). The sort of countries based on the pooled concentration of CTXs was Kiribati (3.904 μg/kg) > Vietnam (1.880 μg/kg) > Macaronesia (1.400 μg/kg) > French (1.261 μg/kg) > China (0.674 μg/kg) > Japan (0.572 μg/kg) > USA (0.463 μg/kg) > Spain (0.224 μg/kg) > UK (0.170 μg/kg) > Fiji (0.162 μg/kg) > Mexico (0.150 μg/kg) > Australia (0.138 μg/kg) > Portugal (0.011 μg/kg). CTXs concentrations in all countries are higher than the safe limits of CTX1C (0.1 μg/kg). However, based on the safe limits of CTX1P, the concentrations of CTXs in just Portugal meet the regulation level (0.01 μg/kg). The minimum and maximum concentrations of CTXs were as observed in Selvagens Islands (0.011 μg/kg) and St Barthelemy (7.875 μg/kg) respectively. CTXs concentrations in all water resources are higher than safe limits of CTX1C (0.1 μg/kg) and CTX1B (0.01 μg/kg). Therefore, it is recommended to carry out continuous control pans of CTXs concentration in fish in different countries and water sources.

Ciguatera Fish Poisoning in the Caribbean Sea and Atlantic Ocean: Reconciling the Multiplicity of Ciguatoxins and Analytical Chemistry Approach for Public Health Safety

Ciguatera is a major circumtropical poisoning caused by the consumption of marine fish and invertebrates contaminated with ciguatoxins (CTXs): neurotoxins produced by endemic and benthic dinoflagellates which are biotransformed in the fish food-web. We provide a history of ciguatera research conducted over the past 70 years on ciguatoxins from the Pacific Ocean (P-CTXs) and Caribbean Sea (C-CTXs) and describe their main chemical, biochemical, and toxicological properties. Currently, there is no official method for the extraction and quantification of ciguatoxins, regardless their origin, mainly due to limited CTX-certified reference materials. In this review, the extraction and purification procedures of C-CTXs are investigated, considering specific objectives such as isolating reference materials, analysing fish toxin profiles, or ensuring food safety control. Certain in vitro assays may provide sufficient sensitivity to detect C-CTXs at sub-ppb levels in fish, but they do not allow for individual identification of CTXs. Recent advances in analysis using liquid chromatography coupled with low- or high-resolution mass spectrometry provide new opportunities to identify known C-CTXs, to gain structural insights into new analogues, and to quantify C-CTXs. Together, these methods reveal that ciguatera arises from a multiplicity of CTXs, although one major form (C-CTX-1) seems to dominate. However, questions arise regarding the abundance and instability of certain C-CTXs, which are further complicated by the wide array of CTX-producing dinoflagellates and fish vectors. Further research is needed to assess the toxic potential of the new C-CTX and their role in ciguatera fish poisoning. With the identification of C-CTXs in the coastal USA and Eastern Atlantic Ocean, the investigation of ciguatera fish poisoning is now a truly global effort.

Regional comparison on ciguatoxicity, hemolytic activity, and toxin profile of the dinoflagellate Gambierdiscus from Kiribati and Malaysia

The dinoflagellates Gambierdiscus and Fukuyoa can produce Ciguatoxins (CTXs) and Maitotoxins (MTXs) that lead to ciguatera poisoning (CP). The CP hotspots, however, do not directly relate to the occurrence of the ciguatoxic Gambierdiscus and Fukuyoa. Species-wide investigations often showed no association between CTX level and the molecular identity of the dinoflagellates. In the Pacific region, Kiribati is known as a CP hotspot, while Malaysia has only three CP outbreaks reported thus far. Although ciguatoxic strains of Gambierdiscus were isolated from both Kiribati and Malaysia, no solid evidence on the contribution of ciguatoxic strains to the incidence of CP outbreak was recorded. The present study aims to investigate the regional differences in CP risks through region-specific toxicological assessment of Gambierdiscus and Fukuyoa. A total of 19 strains of Gambierdiscus and a strain of Fukuyoa were analyzed by cytotoxicity assay of the neuro-2a cell line, hemolytic assay of fish erythrocytes, and high-resolution mass spectrometry. Gambierdiscus from both Kiribati and Malaysia showed detectable ciguatoxicity; however, the Kiribati strains were more hemolytic. Putative 44-methylgambierone was identified as part of the contributors to the hemolytic activity, and other unknown hydrophilic toxins produced can be potentially linked to higher CP incidence in Kiribati.

Ostreopsis Schmidt and Coolia Meunier (Dinophyceae, Gonyaulacales) from Cook Islands and Niue (South Pacific Ocean), including description of Ostreopsis tairoto sp. nov

It is important to decipher the diversity and distribution of benthic dinoflagellates, as there are many morphologically indistinct taxa that differ from one another in production of potent toxins. To date, the genus Ostreopsis comprises twelve described species, of which seven are potentially toxic and produce compounds presenting a threat to human and environmental health. In this study, isolates previously identified as "Ostreopsis sp. 3" were sampled from the area where it was first reported, Rarotonga, Cook Islands, and have been taxonomically and phylogenetically characterised as Ostreopsis tairoto sp. nov. Phylogenetically, the species is closely related to "Ostreopsis sp. 8", O. mascarenensis, "O. sp. 4", O. fattorussoi, O. rhodesiae and O. cf. siamensis. Previously, it was considered a part of the O. cf. ovata complex but can be distinguished from O. cf. ovata based on the small pores identified on this study, and from O. fattorussoi and O. rhodesiae based on relative lengths of the 2' plates. No known palytoxin -like compounds were detected in strains investigated in this study. Strains of O. lenticularis, Coolia malayensis and C. tropicalis were also identified and described. This study advances our knowledge of biogeography, distribution, and toxins of Ostreopsis and Coolia species.