Effects of salinity variation on growth and yessotoxin composition in the marine dinoflagellate Lingulodinium polyedra from a Skagerrak fjord system (western Sweden)

Combined toxic effects of yessotoxin and polystyrene on the survival, reproduction, and population growth of rotifer Brachionus plicatilis at different temperatures

Yessotoxin (YTX) is a disulfated toxin produced by harmful dinoflagellates and causes risks to aquatic animals. Polystyrene (PS) microplastics could absorb toxins in seawaters but pose threats to organism growth. In this study, the combined toxic effects of YTX (0, 20, 50, and 100 µg L-1) and PS (0, 5, and 10 µg mL-1) on the survival, reproduction, and population growth of marine rotifer Brachionus plicatilis at 20 °C, 25 °C, and 30 °C were evaluated. Results indicated that the survival time (S), time to first batch of eggs (Ft), total offspring per rotifer (Ot), generational time (T0), net reproduction rate (R0), intrinsic growth rate (rm), and population growth rate (r) of rotifers were inhibited by YTX and PS at 25 °C and 30 °C. Low temperature (20 °C) improved the life-table parameters T0, R0, and rm at YTX concentrations less than 100 µg L-1. Temperature, YTX, and PS had interactive effects on rotifers' S, Ft, Ot, T0, R0, rm, and r. The combined negative effects of YTX and PS on rotifers' survival, reproduction, and population growth were significantly enhanced at 30 °C. These findings emphasized the importance of environmental temperature in studying the interactive effects of microplastics and toxins on the population growth of zooplankton in eutrophic seawaters.

Gonyaulax montresoriae sp. nov. (Dinophyceae) from the Adriatic Sea produces predominantly yessotoxin

Yessotoxin is one of the shellfish toxins leading to mussel farm closures in the Adriatic Sea of Italy. Two putative Gonyaulax spinifera strains GSA0501 and GSA0602 are known as yessotoxins producers, but their identities have remained elusive since 2005. To address this gap, we established five Gonyaulax strains by incubating sediments from the Adriatic Sea and subsequently isolating single cells. Both cyst and theca morphology were examined using light and scanning electron microscopy. In addition, LSU and/or SSU rRNA gene sequences were obtained for all strains. Two strains produce cysts resembling Spiniferites mirabilis and one strain was related to S. scabratus. The other two strains are described as Gonyaulax montresoriae sp. nov., characterized by a high cingular displacement and overhang, along with two unequal antapical spines. Cysts of G. montresoriae are pear-shaped, showing a smooth surface and exclusively gonal processes with perforations at the base, the latter similar to S. lazus. LSU rRNA gene sequence comparison suggests that the G. spinifera strain GSA0501 isolated from the Adriatic Sea in 2005 should also be identified as G. montresoriae. Maximum likelihood and Bayesian inference analyses based on LSU and SSU rRNA gene sequences reveal that G. montresoriae is monophyletic, and close to several toxic strains of presumable Gonyaulax spinifera from the Adriatic Sea and New Zealand, whose taxonomic positions are uncertain. One strain of G. montresoriae was examined for yessotoxin production using LC-MS/MS, and found to produce predominantly yessotoxin at a concentration of 3.0 pg cell-1. Our results highlight the rich diversity and risks associated with Gonyaulax species in the Mediterranean Sea.

Naturally and Anthropogenically Induced Lingulodinium polyedra Dinoflagellate Red Tides in the Galician Rias (NW Iberian Peninsula)

Despite the fact that the first red tide reported on the coasts of the Iberian Peninsula was due to Lingulodinium polyedra, knowledge about their frequency and, particularly, about the environmental conditions contributing to bloom initiation is still scarce. For this reason, L. polyedra bloom episodes were observed and studied in three Galician rias during the summer season based on the 1993-2008 record database period; additionally, samples were collected in summer 2008. Proliferations of L. polyedra occurred in the rias of Ares and Barqueiro in June and August, respectively, while in the Ria of Coruña, they persisted from the end of June to early September. Red tides developed when the surface temperature reached 17 °C, with "seasonal thermal window" conditions, and when salinities were ≥30, i.e., an "optimal salinity window"; when these parameters were lower than these thresholds, cyst germination decreased. A cyst transport mechanism from sediments to the surface must also exist; this mechanism was found to be natural (tidal currents) in the ria of Barqueiro or anthropogenic (dredging) in the rias of Ares and Coruña. Surface temperatures during summer were usually favorable for cyst germination (85 to 100%) during the 1993-2008 period; however, water temperatures below 10 m depth only rarely reached the 17 °C threshold (2 to 18%). During this 16-year period, dredging activities could explain 71% (Coruña) and 44% (Ares) of the recorded bloom events. When a bloom episode developed in early summer, favorable conditions did not lead to a new red tide, probably due to the lag period required by cysts for germination. Moreover, blooms did not develop when high densities of diatoms (>1,000,000 cells·L-1) remained in the water column as a result of summer upwelling pulses occurring in specific years. The temperature-sediment disturbance pattern found in this study provides a useful tool for the prevention of eventual risks resulting from red tides of this dinoflagellate.

Salinity decline promotes growth and harmful blooms of a toxic alga by diverting carbon flow

Global climate change intensifies the water cycle and makes freshest waters become fresher and vice-versa. But how this change impacts phytoplankton in coastal, particularly harmful algal blooms (HABs), remains poorly understood. Here, we monitored a coastal bay for a decade and found a significant correlation between salinity decline and the increase of Karenia mikimotoi blooms. To examine the physiological linkage between salinity decreases and K. mikimotoi blooms, we compare chemical, physiological and multi-omic profiles of this species in laboratory cultures under high (33) and low (25) salinities. Under low salinity, photosynthetic efficiency and capacity as well as growth rate and cellular protein content were significantly higher than that under high salinity. More strikingly, the omics data show that low salinity activated the glyoxylate shunt to bypass the decarboxylation reaction in the tricarboxylic acid cycle, hence redirecting carbon from CO2 release to biosynthesis. Furthermore, the enhanced glyoxylate cycle could promote hydrogen peroxide metabolism, consistent with the detected decrease in reactive oxygen species. These findings suggest that salinity declines can reprogram metabolism to enhance cell proliferation, thus promoting bloom formation in HAB species like K. mikimotoi, which has important ecological implications for future climate-driven salinity declines in the coastal ocean with respect to HAB outbreaks.

Toxic effects of combined exposure to homoyessotoxin and nitrite on the survival, antioxidative responses, and apoptosis of the abalone Haliotis discus hannai

Homoyessotoxin (homo-YTX) and nitrite (NO2-N), released during harmful dinoflagellate cell lysis adversely affect abalones. However, their toxicity mechanisms in shellfish remain unclear. This study investigated the economic abalone species Haliotis discus hannai exposed to varying concentrations of homo-YTX (0, 2, 5, and 10 µg L-1) and NO2-N (0, 3, and 6 mg L-1) on the basis of their 12 h LC50 values (5.05 µg L-1 and 4.25 mg L-1, respectively) and the environmentally relevant dissolved concentrations during severe dinoflagellate blooms, including mixtures. The test abalones were exposed to homo-YTX and NO2-N for 12 h. The mortality rate (D), reactive oxygen species (ROS) levels, antioxidant defense capabilities, and expression levels of antioxidant-related, Hsp-related, and apoptosis-related genes in abalone gills were assessed. Results showed that the combined exposure to homo-YTX and NO2-N increased the D and ROS levels and upregulated B-cell lymphoma-2 (BCL2)-associated X (BAX) and caspase3 (CASP3) expression levels while reducing glutathione peroxidase (GPx) activity and GPx, CuZnSOD, and BCL2 expression levels. High concentrations of homo-YTX (10 µg L-1) and NO2-N (6 mg L-1) solutions and the combinations of these toxicants inhibited the activities of superoxide dismutase (SOD) and catalase (CAT) and downregulated the expression levels of MnSOD, CAT, Hsp70, and Hsp90. The ROS levels were negatively correlated with the activities of SOD, CAT, and GPx and the expression levels of MnSOD, CuZnSOD, CAT, GPx, Hsp70, Hsp90, and BCL2. These results suggest that homo-YTX, in conjunction with NO2-N, induces oxidative stress, disrupts antioxidant defense systems, and triggers caspase-dependent apoptosis in the gills of abalone. ROS-mediated antioxidative and heat-shock responses and apoptosis emerge as potential toxicity mechanisms affecting the survival of H. discus hannai due to homo-YTX and NO2-N exposure.

Effect of temperature on growth and yessotoxin production of Protoceratium reticulatum and Lingulodinium polyedra (Dinophyceae) isolates from the Portuguese coast (NE Atlantic)

The dinoflagellates Protoceratium reticulatum and Lingulodinium polyedra are potential yessotoxin (YTX) producers, which have been associated with blooms responsible for economic, social, and ecological impacts around the world. They occur in Iberian waters, but in this region, little is known of their ecophysiology and toxin profiles. This study investigated the growth and toxin production of two strains of each species, from the Portuguese coast, at 15 °C, 19 °C, and 23 °C. Growth curves showed higher growth rates at 19 °C, for both species. YTX and three analogs (homo YTX; 45-OH YTX; 45-OH homo YTX) were investigated by Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS), and the presence of other analogs was investigated by Liquid Chromatography-High-Resolution Mass Spectrometry (LC-HRMS). No evidence of toxin production was found in L. polyedra. By contrast, YTX and 45,55-diOH-YTX were detected in both strains of P. reticulatum. These results confirm P. reticulatum as a source of yessotoxins along the Portuguese coast and add to the observed high intraspecific variability on YTX production of both species, at a global scale.

ROS-mediated physiological activities and apoptotic effect on the survival of abalone (Haliotis discus hannai) under homoyessotoxin and ammonia stresses

Serious dinoflagellate blooms produce homoyessotoxin (homo-YTX) and ammonia (NH3-N) in eutrophic seawaters, posing threats to the healthy development of the mariculture industry. This study aimed to explore the toxicity mechanism of homo-YTX and NH3-N on the survival of abalone, which is important for the ecotoxicological research and cultivation of shellfish. The economy abalone Haliotis discus hannai was placed in homo-YTX (0, 2, 5, and 10 μg L-1) and NH3-N (0, 1.08, and 3.16 mg L-1) and a mixture of the two compounds to determine the survival rate (S), antioxidative responses, physiological activities, and apoptosis of abalone. Results show that the combination of homo-YTX and NH3-N increased the reactive oxygen species level, the malondialdehyde content, and the expression level of BCL2-associated X but decreased S; the activities of superoxide dismutase, catalase, adenosine triphosphatase, glutamic-pyruvic transaminase, xanthine oxidase, lactate dehydrogenase, and lysozyme; and the expression level of B-cell lymphoma-2. The activities of alkaline phosphatase and acid phosphatase in 10 μg L-1 of homo-YTX and 3.16 mg L-1 of NH3-N solutions and in the mixture of the two toxicants decreased. The caspase3 expression level was downregulated in 10 μg L-1 of homo-YTX. These results suggest that homo-YTX and NH3-N enhanced the oxidative stress and lipid peroxidation reactions, inhibited the energy supply, disrupted the metabolic and immune physiological functions, and activated apoptosis in the gills of abalone. ROS-mediated physiological activities and apoptosis were among the potential toxicity mechanisms of the interactive effects of homo-YTX and NH3-N on abalone.

Yessotoxins in Mollusks of the Galician Coast from 2014 to 2022: Variability, Biotransformation, and Resistance to Alkaline Hydrolysis

The presence of yessotoxins (YTXs) was analyzed in 10,757 samples of Galician bivalves from 2014 to 2022. Only YTX and 45-OH YTX were found. YTX was detected in 31% of the samples, while 45-OH YTX was found in 11.6% of them. Among the samples containing YTX, 45-OH YTX was detected in 37.3% of cases. The maximum recorded levels were 1.4 and 0.16 mg of YTX-equivalentsg-1, for YTX and 45-OH YTX, respectively, which are well below the regulatory limit of the European Union. The YTX and 45-OH YTX toxicities in the raw extracts and extracts subjected to alkaline hydrolysis were strongly and linearly related. Due to the lack of homo-YTX in Galician samples, the effect of alkaline hydrolysis on homo-YTX and 45OH-Homo-YTX was only checked in 23 additional samples, observing no negative effect but a high correlation between raw and hydrolyzed extracts. Hydrolyzed samples can be used instead of raw ones to carry out YTXs determinations in monitoring systems, which may increase the efficiency of those systems where okadaic acid episodes are very frequent and therefore a higher number of hydrolyzed samples are routinely analyzed. The presence of YTX in the studied bivalves varied with the species, with mussels and cockles having the highest percentages of YTX-detected samples. The presence of 45-OH YTX was clearly related to YTX and was detected only in mussels and cockles. Wild populations of mussels contained proportionally more 45-OH YTX than those that were raft-cultured. Spatially, toxin toxicities varied across the sampling area, with higher levels in raft-cultured mussels except those of Ría de Arousa. Ría de Ares (ARE) was the most affected geographical area, although in other northern locations, lower toxin levels were detected. Seasonally, YTX and 45-OH YTX toxicities showed similar patterns, with higher levels in late summer and autumn but lower toxicities of the 45-OH toxin in August. The relationship between the two toxins also varied seasonally, in general with a minimum proportion of 45-OH YTX in July-August but with different maximum levels for raft-cultured and wild mussel populations. Interannually, the average toxicities of YTX decreased from 2014 to 2017 and newly increased from 2018 to 2021, but decreased slightly in 2022. The relationship between 45-OH YTX and YTX also varied over the years, but neither a clear trend nor a similar trend for wild and raft mussels was observed.

Behavioural differences underlie toxicity and predation variation in blooms of Prymnesium parvum

Much of the evolutionary ecology of toxic algal blooms (TABs) remains unclear, including the role of algal toxins in the adaptive 'strategies' of TAB-forming species. Most eukaryotic TABs are caused by mixotrophs that augment autotrophy with organic nutrient sources, including competing algae (intraguild predation). We leverage the standing diversity of TABs formed by the toxic, invasive mixotroph Prymnesium parvum to identify cell-level behaviours involved in toxin-assisted predation using direct observations as well as comparisons between genetically distinct low- and high-toxicity isolates. Our results suggest that P. parvum toxins are primarily delivered at close range and promote subsequent prey capture/consumption. Surprisingly, we find opposite chemotactic preferences for organic (prey-derived) and inorganic nutrients between differentially toxic isolates, respectively, suggesting behavioural integration of toxicity and phagotrophy. Variation in toxicity may, therefore, reflect broader phenotypic integration of key traits that ultimately contribute to the remarkable flexibility, diversity, and success of invasive populations.

Occurrence and distribution of lipophilic marine algal toxins in the coastal seawater of Southeast China and the South China Sea

The composition, levels, and spatial distribution of dissolved lipophilic marine algal toxins (LMATs) including cyclic imines (CIs), yessotoxins (YTXs), okadaic acid (OA) and its derivatives, pectenotoxins (PTXs), azaspiracids (AZAs), and brevetoxins (BTXs) in the coastal waters of Southeast China (Xiamen) and the South China Sea (Hainan Island and Beibu Gulf) were investigated and compared for the first time. Dissolved AZA3 was firstly detected in the coastal seawater of China. OA and PTX2 were widely distributed in the three areas studied. Gymnodimine (GYM), 13-desmethyl spirolide C (SPX1), YTX, and homo-yessotoxins (h-YTX) were found mainly in the South China Sea. The average ∑LMAT concentrations in the coastal waters of Xiamen, Hainan Island, and Beibu Gulf were 10.02 ng/L, 4.21 ng/L, and 44.27 ng/L, respectively. More groups and much higher concentrations of LMATs occurred in the South China Sea than that in the other sea areas of China.

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.

Spatial distribution and source of biotoxins in phytoplankton from the South China Sea, China

Marine phycotoxins severely threaten ecosystem health and mariculture. This study investigates the spatial distribution and source of diverse phycotoxins in the South China Sea (SCS), during four 2019/2020 cruises. Saxitoxin (STX) and okadaic acid (OA) -groups, azaspiracids, cyclic imines, pectenotoxins (PTX), yessotoxins, and domoic acid (DA) toxins were analyzed in microalgal samples. PTX2 occurred with the highest (93.5%) detection rate (DR) during all cruises, especially in the Pearl River Estuary (PRE) in June 2019. Homo-yessotoxin (hYTX) and DA were found during three cruises in August 2020, and high DR of hYTX (67.7%, 29.3%) and DA (29.0%, 29.3%) in the PRE and Guangdong coast, respectively, in June 2019 and 2020, peaking at concentrations of 777 pg hYTX L^-1 and 38514 pg DA L^-1. The phycotoxin distribution demonstrated that DA-producing microalgae gathered close to the PRE and Guangdong coast, while hYTX-producing microalgae distributed relatively far offshore. Microalgae producing PTX2- and STX-group toxins were more widely living in the SCS. High-throughput sequencing results suggested that Alexandrium pacificum and Gonyaulax spinifera were responsible for STX-group toxins and hYTX, respectively, while Pseudo-nitzschia cuspidata was the main source of DA. Widely distributed PTX2, hYTX, and DA were reported for the first time in the SCS.

Recommendations for epitypification of dinophytes exemplified by Lingulodinium polyedra and molecular phylogenetics of the Gonyaulacales based on curated rRNA sequence data

Gonyaulacales include a considerable number of harmful algae and to understand their origin and rise, knowledge of the evolutionary relationships is necessary. Many scientific names of protists introduced prior to the availability of DNA analytics are ambiguous and impede communication about biological species and their traits in the microbial world. Strains of Lingulodinium polyedra were established from its type locality in the Kiel Fjord (Germany) to clarify its taxonomy. Moreover, the phylogeny of Gonyaulacales was inferred based on 329 rRNA sequence accessions compiled in a curated sequence data base, with as much as possible type material equivalents included. Gonyaulacales were monophyletic and segregated into seven lineages at high systematic level, of which †Lingulodiniaceae constituted the first branch of the Gonyaulacales. Their type species had a plate formula APC (Po, X, cp), 3', 3a, 6'' 6c, 6s, 6''', 2'''' and is taxonomically clarified by epitypification. Recommendations for this important taxonomic tool are provided, with a focus on microorganisms. Most gonyaulacalean taxa established at generic rank are monophyletic, with Alexandrium, Coolia and Gonyaulax as notable exceptions. From an evolutionary perspective, gonyaulacalean dinophytes with quinqueform hypotheca are monophyletic and derive from a paraphyletic group showing the sexiform configuration.

Bioluminescence and toxicity as driving factors in harmful algal blooms: Ecological functions and genetic variability

Dinoflagellates are an ecologically important group of marine microbial eukaryotes with a remarkable array of adaptive strategies. It is ironic that two of the traits for which dinoflagellates are best known, toxin production and bioluminescence, are rarely linked when considering the ecological significance of either. Although dinoflagellate species that form some of the most widespread and frequent harmful algal blooms (HABs) are bioluminescent, the molecular and eco-evolutionary associations between these two traits has received little attention. Here, the major themes of biochemistry and genetics, ecological functions, signaling mechanisms, and evolution are addressed, with parallels and connections drawn between the two. Of the 17 major classes of dinoflagellate toxins, only two are produced by bioluminescent species: saxitoxin (STX) and yessotoxin. Of these, STX has been extensively studied, including the identification of the STX biosynthetic genes. While numerous theories have been put forward as to the eco-evolutionary roles of both bioluminescence and toxicity, a general consensus is that both function as grazing deterrents. Thus, both bioluminescence and toxicity may aid in HAB initiation as they alleviate grazing pressure on the HAB species. A large gap in our understanding is the genetic variability among natural bloom populations, as both toxic and non-toxic strains have been isolated from the same geographic location. The same applies to bioluminescence, as there exist both bioluminescent and non-bioluminescent strains of the same species. Recent evidence demonstrating that blooms are not monoclonal events necessitates a greater level of understanding as to the genetic variability of these traits among sub-populations as well as the mechanisms by which cells acquire or lose the trait, as sequence analysis of STX+ and STX- species indicate the key gene required for toxicity is lost rather than gained. While the extent of genetic variability for both bioluminescence and toxicity among natural HAB sub-populations remains unknown, it is an area that needs to be explored in order to gain greater insights into the molecular mechanisms and environmental parameters driving HAB evolution.

Functional Genomics Differentiate Inherent and Environmentally Influenced Traits in Dinoflagellate and Diatom Communities

Dinoflagellates and diatoms are among the most prominent microeukaryotic plankton groups, and they have evolved different functional traits reflecting their roles within ecosystems. However, links between their metabolic processes and functional traits within different environmental contexts warrant further study. The functional biodiversity of dinoflagellates and diatoms was accessed with metatranscriptomics using Pfam protein domains as proxies for functional processes. Despite the overall geographic similarity of functional responses, abiotic (i.e., temperature and salinity; ~800 Pfam domains) and biotic (i.e., taxonomic group; ~1500 Pfam domains) factors influencing particular functional responses were identified. Salinity and temperature were identified as the main drivers of community composition. Higher temperatures were associated with an increase of Pfam domains involved in energy metabolism and a decrease of processes associated with translation and the sulfur cycle. Salinity changes were correlated with the biosynthesis of secondary metabolites (e.g., terpenoids and polyketides) and signal transduction processes, indicating an overall strong effect on the biota. The abundance of dinoflagellates was positively correlated with nitrogen metabolism, vesicular transport and signal transduction, highlighting their link to biotic interactions (more so than diatoms) and suggesting the central role of species interactions in the evolution of dinoflagellates. Diatoms were associated with metabolites (e.g., isoprenoids and carotenoids), as well as lysine degradation, which highlights their ecological role as important primary producers and indicates the physiological importance of these metabolic pathways for diatoms in their natural environment. These approaches and gathered information will support ecological questions concerning the marine ecosystem state and metabolic interactions in the marine environment.

Structure Elucidation and Relative Toxicity of (24R)-24-Hydroxyyessotoxin from a Namibian Isolate of Gonyaulax spinifera

Liquid chromatography-high-resolution mass spectrometry (LC-HRMS) analysis of a Namibian strain of Gonyaulax spinifera showed the presence of a number of yessotoxins (YTXs). Principal among these were YTX (1), homoYTX (2), and a tentative hydroxylated analogue that did not correspond to any previously confirmed YTX structures. Culturing the G. spinifera strain afforded sufficient biomass for purification of the new analogue through a series of solvent partitioning and chromatographic steps, yielding ∼0.9 mg as a solid. NMR spectroscopy, ion-trap mass spectrometry, and HRMS identified the new analogue as 24-hydroxyYTX (7). Purified 24-hydroxyYTX was quantitated by NMR, and its relative toxicity evaluated using two embryonic zebrafish toxicity assays. 24-HydroxyYTX demonstrated reduced toxicity compared to YTX.