Morphology and molecular phylogeny of a new PST-producing dinoflagellate species: Alexandrium fragae sp. nov. (Gonyaulacales, dinophyceae)

Effects of temperature and nutrients on growth and toxicity of Alexandrium affine from southeastern Gulf of California

An Alexandrium affine strain (AAJQ-1) from San José Island, Gulf of California was characterized for growth and toxicology. Fivefold of f/2 + Se cultures were incubated for 34 days in a temperature gradient (21-29 °C). Aliquots were collected every third day for cell counting, toxin determination, and nutrient analyses. In this study ELISA method was used to evaluate the PSP toxin production due to the lower detection limit than the HPLC method. The highest cell density (6724 cells mL-1) and growth rate (0.22 day-1) were obtained at 27 °C and they were related to temperature in all treatments. Cell density showed negative correlation with nitrate at temperatures ≥23 °C, and with orthophosphate 27 °C, furthermore, these correlations promote the toxin production (0.05-0.45 fmol STX cell-1); beyond that nitrite at high temperature seems to promote toxin production, which has not been sufficiently documented.

Polyphyletic origin of saxitoxin biosynthesis genes in the marine dinoflagellate Alexandrium revealed by comparative transcriptomics

The marine dinoflagellate Alexandrium is known to form harmful algal blooms, and at least 14 species within the genus can produce saxitoxins (STXs). STX biosynthesis genes (sxt) are individually revealed in toxic dinoflagellates; however, the evolutionary history remains controversial. Herein, we determined the transcriptome sequences of toxic Alexandrium (A. catenella and A. pacificum) and non-toxic Alexandrium (A. fraterculus and A. fragae) and characterized their sxt by focusing on evolutionary events and STX production. Comparative transcriptome analysis revealed higher homology of the sxt in toxic Alexandrium than in non-toxic species. Notably, non-toxic Alexandrium spp. were found to have lost two sxt core genes, namely sxtA4 and sxtG. Expression levels of 28 transcripts related to eight sxt core genes showed that sxtA, sxtG, and sxtI were relatively high (>1.5) in the toxic group compared to the non-toxic group. In contrast, the non-toxic group showed high expression levels in sxtU (1.9) and sxtD (1.7). Phylogenetic tree comparisons revealed distinct evolutionary patterns between 28S rDNA and sxtA, sxtB, sxtI, sxtD, and sxtU. However, similar topology was observed between 28S rDNA, sxtS, and sxtH/T. In the sxtB and sxtI phylogeny trees, toxic Alexandrium and cyanobacteria were clustered together, separating from non-toxic species. These suggest that Alexandrium may acquire sxt genes independently via horizontal gene transfer from toxic cyanobacteria and other multiple sources, demonstrating monocistronic transcripts of sxt in dinoflagellates.

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.

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.

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.

Diversity and distribution of harmful microalgae in the Gulf of Thailand assessed by DNA metabarcoding

Information on the diversity and distribution of harmful microalgae in the Gulf of Thailand is very limited and mainly based on microscopic observations. Here, we collected 44 water samples from the Gulf of Thailand and its adjacent water (Perhentian Island, Malaysia) for comparison in 2018. DNA metabarcoding was performed targeting the partial large subunit ribosomal RNA gene (LSU rDNA D1-D3) and the internal transcribed spacers (ITS1 and ITS2). A total of 50 dinoflagellate genera (made up of 72 species) were identified based on the LSU rDNA dataset, while the results of ITS1 and ITS2 datasets revealed 33 and 32 dinoflagellate genera comprising 69 and 64 species, respectively. Five potentially toxic Pseudo-nitzschia (Bacillariophyceae) species were detected, with four as newly recorded species in the water (Pseudo-nitzschia americana/brasilliana, Pseudo-nitzschia simulans/delicatissima, P. galaxiae and P. multistriata). The highest relative abundances of P. galaxiae and P. multistriata were found in Trat Bay and Chumphon (accounting for 0.20% and 0.06% of total ASVs abundance, respectively). Three paralytic shellfish toxin producing dinoflagellate species were detected: Alexandrium tamiyavanichii, Alexandrium fragae, and Gymnodinium catenatum. The highest abundance of A. tamiyavanichii was found in the surface sample of Chumphon (CHO7 station), accounting for 1.95% of total ASVs abundance. Two azaspiracid producing dinoflagellate species, Azadinium poporum ribotype B, Azadinium spinosum ribotype A, and a pinnatoxin producing dinoflagellate species Vulcanodinium rugosum, with two ribotypes B and C, were revealed from the datasets although with very low abundances. Six fish killing dinoflagellate species, including Margalefidinium polykrikoides group IV, Margalefidinium fulvescens, Karenia mikimotoi, Karenia selliformis ribotype B, Karlodinium australe, and Karlodinium digitatum were detected and all representing new records in this area. The findings of numerous harmful microalgal species in the Gulf of Thailand highlight the potential risk of human intoxication and fish killing events.

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.

The Latin America and Caribbean HAB status report based on OBIS and HAEDAT maps and databases

Harmful Algae Blooms (HAB) have been documented for at least fifty years in Latin America and the Caribbean (LAC), however, their impacts at social, ecological and economic levels are still little known. To contribute to the impact assessment of HABs in LAC region, the available information in HAEDAT, OBIS, CAREC, and CARPHA databases, and scientific literature was analyzed. This historical analysis allows identification of the main syndromes and causal organisms. Considering the existence of two regional working groups of the Intergovernmental Oceanographic Commission (IOC): Algas Nocivas del Caribe (ANCA) and Floraciones Algales Nocivas en Sudamérica (FANSA), representing Central American/Caribbean and South American countries, respectively, the analysis is presented both globally and subregional. For the FANSA region, the HAEDAT data base listed 249 records from 1970 to 2019, with a total of 1432 human intoxications, including 37 fatalities. The majority of these events comprised Paralytic Shellfish Toxins (49%), Diarrhetic Shellfish Toxins (34%), Cyanotoxins (12%) and 6 % other toxins. The total number of harmful taxa in the OBIS database includes 79 species distributed over 25 genera. The most commonly reported species are Alexandrium catenella/tamarense, Gymnodinium catenatum and the Dinophysis acuminata complex. Two new species Prorocentrum caipirignum Fraga, Menezes and Nascimento and Alexandrium fragae Branco and Menezes were newly described from Brazilian waters. In the ANCA region, HAEDAT listed 131 records from 1956 to 2018. The main problems are PSP and Ciguatera and common HAB taxa are Gambierdiscus, Gymnodinium, Pyrodinium, Alexandrium and Dinophysis. The most reported HAB forming species are Gymnodinium catenatum, Pyrodinium bahamense and Gambierdiscus spp. In recent years Margalefidinium polykrikoides blooms have become frequent, causing fish and invertebrates massive mortalities and impacts on touristic activities. In the LAC region, the greatest economic losses were produced by ichthyotoxic massive events causing salmon deaths associated to Pseudochattonella verruculosa and Alexandrium catenella in Chile and tuna deaths related to Tripos furca and Chattonella spp. in the Mexican Pacific. In the last decade, several studies in LAC have linked HAB events with local mesoscale oceanographic and atmospheric phenomena. Trends analyzed up to 2019 are related to the increasing awareness about presence of toxic species, the geographical expansion of already known species, the detection of new toxins for the region, and HAB events duration and/or impacts.

Morphological and phylogenetic data do not support the split of Alexandrium into four genera

A recently published study analyzed the phylogenetic relationship between the genera Centrodinium and Alexandrium, confirming an earlier publication showing the genus Alexandrium as paraphyletic. This most recent manuscript retained the genus Alexandrium, introduced a new genus Episemicolon, resurrected two genera, Gessnerium and Protogonyaulax, and stated that: "The polyphyly [sic] of Alexandrium is solved with the split into four genera". However, these reintroduced taxa were not based on monophyletic groups. Therefore this work, if accepted, would result in replacing a single paraphyletic taxon with several non-monophyletic ones. The morphological data presented for genus characterization also do not convincingly support taxa delimitations. The combination of weak molecular phylogenetics and the lack of diagnostic traits (i.e., autapomorphies) render the applicability of the concept of limited use. The proposal to split the genus Alexandrium on the basis of our current knowledge is rejected herein. The aim here is not to present an alternative analysis and revision, but to maintain Alexandrium. A better constructed and more phylogenetically accurate revision can and should wait until more complete evidence becomes available and there is a strong reason to revise the genus Alexandrium. The reasons are explained in detail by a review of the available molecular and morphological data for species of the genera Alexandrium and Centrodinium. In addition, cyst morphology and chemotaxonomy are discussed, and the need for integrative taxonomy is highlighted.