Representatives of the marine dinophyte family Amphidomataceae produce lipophilic phycotoxins called azaspiracids (AZA) which may cause azaspiracid shellfish poisoning (AZP) in humans after consumption of contaminated seafood. Three of the four known toxigenic species are observed frequently in the eastern North Atlantic. In 2018, a research survey was performed to strengthen knowledge on the distribution and abundance of toxigenic Amphidomataceae and their respective toxins in Irish coastal waters and in the North Sea. Species-specific quantification of the three toxigenic species (Azadinium spinosum, Azadinium poporum and Amphidoma languida) was based on recently developed qPCR assays, whose performance was successfully validated and tested with specificity tests and spike experiments. The multi-method approach of on-board live microscopy, qPCR assays and chemical AZA-analysis revealed the presence of Amphidomataceae in the North Atlantic including the three targeted toxigenic species and their respective AZA analogues (AZA-1,-2,-33,-38,-39). Azadinium spinosum was detected at the majority of Irish stations with a peak density of 8.3 x 10 4 cells L-1 and AZA (AZA-1,-2,-33) abundances up to 1,274 pg L-1. Amphidoma languida was also present at most Irish stations but appeared in highest abundance in a bloom at a central North Sea station with a density of 1.2 x 10 5 cells L-1 and an AZA (AZA-38,-39) abundances of 618 pg L-1. Azadinium poporum was detected sporadically at the Irish south coast and North Sea and was rather low in abundance during this study. The results confirmed the wide distribution and frequent occurrence of the target species in the North Atlantic area and revealed, for the first time, bloom abundances of toxigenic Amphidomataceae in this area. This emphasizes the importance of future studies and monitoring of amphidomatacean species and their respective AZA analogues in the North Atlantic.
Azaspiracids (AZA) are lipophilic marine biotoxins associated with shellfish poisoning which are produced by some species of Amphidomataceae. Diversity and global biogeography of this family are still poorly known. In summer 2017 plankton samples were collected from the central Labrador Sea and western Greenland coast from 64°N (Gothaab Fjord) to 75°N for the presence of Amphidomataceae and AZA. In the central Labrador Sea, light microscopy revealed small Azadinium-like cells (9200 cells l −1 ). Clonal strains established from plankton samples and scanning electron microscopy of fixed plankton samples revealed at least eight species of Amphidomataceae: Azadinium obesum, Az. trinitatum, Az. dexteroporum, Az. spinosum, Az. polongum, Amphidoma languida, Azadinium spec., and a new species described here as Azadinium perforatum sp. nov. The new species differed from other Azadinium species by the presence of thecal pores on the pore plate. All samples, including cultured strains, filtered seawater samples, and solid phase adsorption toxin tracking (SPATT) samplers deployed during the expedition in a continuous water-sampling system (FerryBox), were negative for AZA. DNA samples and PCR assays were positive for Amphidomataceae from most stations, whereas species-specific assays for three toxigenic species were rarely positive (two stations for Az. poporum, one station for Am. languida). The results highlight the presence of Amphidomataceae in the area but the lack of toxins and low abundance of toxigenic species currently indicate a low risk of toxic Amphidomataceae blooms in Arctic coastal waters.
SUMMARY Prorocentrum comprises a unique group of dinophytes with several apomorphic traits, such as an apical insertion of flagella and the presence of two major, large thecal plates. Species delimitation is challenging, especially for morphologically very similar, small planktonic species. Contemporary analyses, including SEM studies and molecular phylogenetics of type material, are not available for many described species. Based on six strains isolated from Antarctic, subarctic and North Atlantic waters, Prorocentrum pervagatum sp. nov. is described. Prorocentrum pervagatum was small (12–16 μm long and deep), oval to round in outline, and moderately compressed. One small, pyrenoid‐like structure was faintly visible in some cells. Rod‐like, long trichocysts were present. Cells had one distinct apical spine (1.1–1.7 μm in length) visible in light microscopy. The plate surface appeared smooth in light microscopy with few pores located close to the plate margin visible in empty thecae. Electron microscopy revealed plates to be densely covered by small projections and two size classes of thecal pores. Cells had a row of mostly four large pores in apical‐ventral position on the right thecal plate. The periflagellar area consisted of eight small platelets. The apical spine was formed by platelet six. In molecular phylogenetics, P. pervagatum was part of a species group generally exhibiting small size and spiny thecal ornamentation, together with Prorocentrum cordatum and Prorocentrum obtusidens. The new species is distinct in DNA trees and differs from the protologues of other small species of Prorocentrum by the unique combination of size, shape (i.e. only moderately compressed or round), presence of a distinct apical spine, and position of thecal pores (i.e. located at the plate margins only). Its clear description and illustration may stimulate similar work of other small species of Prorocentrum, particularly including the re‐investigation of taxa with historical names collected at the corresponding type localities.
Species of the planktonic dinoflagellates Azadinium and Amphidoma are small, inconspicuous and difficult, if not impossible to be identified and differentiated by light microscopy. Within this group, there are some species that produce the marine biotoxin azaspiracid (AZA) while others are non-toxigenic, therefore a requirement exists for precise species identification. A quantitative polymerase chain reaction (qPCR) assay for molecular detection and quantification of one of the toxigenic species, Amphidoma languida, was designed and extensively tested. The assay was highly specific and sensitive to detect and quantify down to 10 target gene copies (corresponding to ca. 0.05 cells) per reaction. DNA cell quota and copy number cell −1 were constant for four different Am. languida strains, and for one strain they were shown to be stable at various time points throughout the growth cycle. Recovery of known cell numbers of Am. languida spiked into natural samples was 95-103%, and the assay was successfully tested on field samples collected from Irish coastal waters. This new qPCR assay is a valuable tool for routine monitoring for the prevention of AZA-shellfish-poisoning caused by the consumption of contaminated shellfish and is a supportive tool for studies on the biogeography of this AZA-producing species.
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.
The cosmopolitan, potentially toxic dinoflagellate Protoceratium reticulatum possesses a fossilizable cyst stage which is an important paleoenvironmental indicator. Slight differences in the internal transcribed spacer ribosomal DNA (ITS rDNA) sequences of P. reticulatum have been reported, and both the motile stage and cyst morphology of P. reticulatum display phenotypic plasticity, but how these morpho-molecular variations are related with ecophysiological preferences is unknown. Here, 55 single cysts or cells were isolated from localities in the Northern (Arctic to subtropics) and Southern Hemispheres (Chile and New Zealand), and in total 34 strains were established. Cysts and/or cells were examined with light microscopy and/or scanning electron microscopy. Large subunit ribosomal DNA (LSU rDNA) and/or ITS rDNA sequences were obtained for all strains/isolates. All strains/isolates of P. reticulatum shared identical LSU sequences except for one strain from the Mediterranean Sea that differs in one position, however ITS rDNA sequences displayed differences at eight positions. Molecular phylogeny was inferred using maximum likelihood and Bayesian inference based on ITS rDNA sequences. The results showed that P. reticulatum comprises at least three ribotypes (designated as A, B, and C). Ribotype A included strains from the Arctic and temperate areas, ribotype B included strains from temperate regions only, and ribotype C included strains from the subtropical and temperate areas. The average ratios of process length to cyst diameter of P. reticulatum ranged from 15% in ribotype A, 22% in ribotype B and 17% in ribotype C but cyst size could overlap. Theca morphology was indistinguishable among ribotypes. The ITS-2 secondary structures of ribotype A displayed one CBC (compensatory change on two sides of a helix pairing) compared to ribotypes B and C. Growth response of one strain from each ribotype to various temperatures was examined. The strains of ribotypes A, B and C exhibited optimum growth at 15°C, 20°C and 20-25°C, respectively, thus corresponding to cold, moderate and warm ecotypes. The profiles of yessotoxins (YTXs) were examined for 25 strains using liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). The parent compound yessotoxin (YTX) was produced by strains of ribotypes A and B, but not by ribotype C strains, which only produced the structural variant homoyessotoxin (homoYTX). Our results support the notion that there is significant intra-specific variability in Protoceratium reticulatum and the biogeography of the different ribotypes is consistent with specific ecological preferences.
Some species of the dinophytes Azadinium and Amphidoma (Amphidomataceae) produce azaspiracids (AZA), lipophilic polyether compounds responsible for Azaspiracid Shellfish Poisoning (AZP) in humans after consumption of contaminated seafood. Toxigenic Amphidomataceae are known to occur in the North Atlantic and the North Sea area, but little is known about their importance in Danish coastal waters. In 2016, 44 Stations were sampled on a survey along the Danish coastline, covering the German Bight, Limfjord, the Kattegat area, Great Belt and Kiel Bight. Samples were analysed by live microscopy, liquid chromatography-tandem mass spectrometry (LC-MS/MS) and quantitative polymerase-chain-reaction (qPCR) on the presence of Amphidomataceae and AZA. Amphidomataceae were widely distributed in the area, but were below detection limit on most of the inner Limfjord stations. Cell abundances of the three toxigenic species, determined with species-specific qPCR assays on Azadinium spinosum, Az. poporum and Amphidoma languida, were generally low and restricted to the North Sea and the northern Kattegat, which was in agreement with the distribution of the generally low AZA abundances in plankton samples. Among the toxigenic species, Amphidoma languida was dominant with highest cell densities up to 3 × 10 3 cells L −1 on North Sea stations and at the western entrance of the Limfjord. Azaspiracids detected in plankton samples include low levels of AZA-1 at one station of the North Sea, and higher levels of AZA-38 and -39 (up to 1.5 ng L −1 ) in the North Sea and the Limfjord entrance. Furthermore, one new AZA (named AZA-63) was discovered in plankton of two North Sea stations. Morphological, molecular, and toxinological characterisation of 26 newly established strains from the area confirmed the presence of four amphidomatacean species (Az. obesum, Az. dalianense, Az. poporum and Am. languida). The single new strain of Az. poporum turned out as a member of Ribotype A2, which was previously only known from the Mediterranean. Consistent with some of these Mediterranean A2 strains, but different to the previously established AZA-37 producing Az. poporum Ribotype A1 strains from Denmark, the new strain did not contain any AZA. Azaspiracids were also absent in all Az. obesum and Az. dalianense strains, but AZA-38 and -39 were found in all Am. languida strains with total AZA cell quotas ranging from 0.08 up to 94 fg cell −1 . In conclusion, AZA-producing microalgae and their respective toxins were low in abundance but widely present in the area, and thus might be considered in local monitoring programs to preserve seafood safety in Danish coastal waters. the respective biotoxins, which can cause large fish kills or potential health problems in human seafood consumers. Most threatening for Danish waters currently are fish killing species of Pseudochattonella, which since about 20 years has become well established in Scandinavian waters and form recurrent massive blooms in the North Sea and Skagerrak (Jakobsen et al., 2012). Another fish ki...
Prorocentrum comprises dinophytes with several unique traits, including the presence of two large thecal plates and apical insertion of flagella. Species delimitation for many small and similar planktonic species is challenging, as SEM analyses and DNA sequence information of type material are rarely available. Based on a strain from the North Atlantic Prorocentrum spinulentum, sp. nov. is described here. Cells were small (9.0–12.8 µm long, 8.5–11.9 µm deep), oval to almost round in lateral view and moderately compressed. The ovoid nucleus was in median or slightly sub-median position on the cells ventral side. The plate surface appeared spiny in light microscopy with thecal pores visible in empty thecae. Electron microscopy revealed plates densely covered by relatively long spines and two size classes of thecal pores. The periflagellar area consisted of 8 platelets, and there was a prominent wing (ca. 1 µm wide and long) on platelet 1. The new species is distinct in DNA trees and embedded in the Prorocentrum shikokuense species group. It differs from the protologues of other small species of Prorocentrum by the unique combination of cell size and shape, the presence of long spines on the thecal plate surface and scattered thecal pores. The thorough morphological description of this species, representing a previously uncharacterised lineage within Prorocentrum, increases and improves our knowledge of the diversity within this important group of planktonic organisms.
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