Ribosomal DNA sequences discriminate among toxic and non-toxic Pseudonitzschia species

Diversity and toxicity of the planktonic diatom genus Pseudo-nitzschia from coastal and offshore waters of the Southeast Pacific, including Pseudo-nitzschia dampieri sp. nov

To expand knowledge of Pseudo-nitzschia species in the Southeast Pacific, we isolated specimens from coastal waters of central Chile (36°S-30°S), the Gulf of Corcovado, and the oceanic Robinson Crusoe Island (700 km offshore) and grew them into monoclonal strains. A total of 123 Pseudo-nitzschia strains were identified to 11 species based on sequencing of the ITS region of the nuclear rDNA and on ultrastructural and morphometric analyses of the frustule in selected representatives of each clade: P. australis, P. bucculenta, P. cf. chiniana, P. cf. decipiens, P. fraudulenta, P. hasleana, P. multistriata, P. plurisecta, P. cf. sabit, the new species P. dampieri sp. nov., and one undescribed species. Partial 18S and 28S rDNA sequences, including the hypervariable V4 and D1-D3 regions used for barcoding, were gathered from representative strains of each species to facilitate future metabarcoding studies. Results showed different levels of genetic, and at times ultrastructural, diversity among the above-mentioned entities, suggesting morphological variants (P. bucculenta), rapidly radiating complexes with ill-defined species boundaries (P. cf. decipiens and P. cf. sabit), and the presence of new species (P. dampieri sp. nov., Pseudo-nitzschia sp. 1, and probably P. cf. chiniana). Domoic acid (DA) was detected in 18 out of 82 strains tested, including those of P. australis, P. plurisecta, and P. multistriata. Toxicity varied among species mostly corresponding to expectations from previous reports, with the prominent exception of P. fraudulenta; DA was not detected in any of its 10 strains tested. In conclusion, a high diversity of Pseudo-nitzschia exists in Chilean waters, particularly offshore.

Taxonomy and abundance of epibenthic Prorocentrum (Dinophyceae) species from the tropical and subtropical Southwest Atlantic Ocean including a review of their global diversity and distribution

In the tropical and subtropical South Atlantic Ocean, studies on the taxonomy and abundance of benthic harmful algae are scarce and the region has been largely under investigated. In this study, morphological descriptions, molecular (LSU rDNA and ITS region) and abundance data of benthic Prorocentrum species from the tropical and subtropical Southwest Atlantic and three oceanic islands are presented. Moreover, a review of global benthic Prorocentrum species richness and distribution is presented. Eleven benthic Prorocentrum species were found in Brazil. Morphological and molecular data on P. borbonicum, P. hoffmannianum, P. lima species complex and P. rhathymum were provided. Prorocentrum panamense, P. cf. caipirignum, P. cf. concavum, P. cf. norrisianum, P. emarginatum/fukuyoi/sculptile complex and two not identified species were observed using scanning electron and/or light microscopy, and morphological descriptions are presented. Prorocentrum lima species complex was found at all investigated sites, in abundances up to 2 × 104 cells g-1 FW at the Northeast Brazil, while maximum abundance of all the remaining species did not exceed 1 × 103 cells g-1 FW. The Fernando de Noronha archipelago can be considered a hotspot of benthic Prorocentrum species diversity, with ten species registered. Data compiled in the literature review shows a clear latitudinal gradient with higher species richness in tropical and subtropical regions relative to temperate areas. It is also evident that there is a bias caused by taxonomic impediment and an uneven sampling effort, with many regions still to be investigated using a combined morphological and molecular effort. Therefore, the current knowledge on the global distribution of benthic Prorocentrum species is likely underestimated.

Morphology and molecular phylogeny of Pleurosigmapacificum sp. nov. (Pleurosigmataceae), a new tropical pelagic species from the Western Pacific Ocean

A new species of pelagic diatom, Pleurosigmapacificumsp. nov., is described from the tropical Western Pacific Ocean. It has the typical features of Pleurosigma, including a slightly sigmoid raphe, intersected transverse and oblique striae, and loculate areolae with external opening slits and internal poroids. Morphologically, P.pacificum belongs to a species group of Pleurosigma with lanceolate valves, including P.atlanticum Heiden & Kolbe, P.nubecula W. Smith, P.indicum Simonsen, and P.simonsenii Hasle. However, P.pacificum differs by its smaller lanceolate valve and smaller intersection angle as well as elliptical areolae without a silica bar. The SSU rDNA and rbcL sequence data place P.pacificum in a basal position relative to other species of Pleurosigma. Our molecular phylogenetic analyses did not support the monophyly of lanceolate and slightly sigmoid species. Thus, the sigmoidality of valve outline cannot be considered as a criterion to define the species group.

The coupling between irradiance, growth, photosynthesis and prymnesin cell quota and production in two strains of the bloom-forming haptophyte, Prymnesium parvum

Prymnesium parvum causes harmful algal blooms worldwide that are often associated with massive fish-kills and subsequent economic losses. Most of our knowledge of the toxicity of P. parvum derives from bioassays since methods for the identification and quantification of their toxins have been lacking. Recently, a quantitation method was developed for the causative lytic toxins, the prymnesins. Here, we for the first time present data on the influence of irradiance on cellular content and production of prymnesins under nutrient replete conditions in two P. parvum strains, which both produce B-type prymnesins. Large differences were observed between the two strains with regard to the influence of irradiance on prymnesin cell quota and production rates. At the highest irradiance level (550 µmol photons m-2 s-1), the cellular prymnesin quota was thirty times higher in strain K-0081 strain than in K-0374. The cellular prymnesin quota and production rates were closely linked to rates of growth and photosynthesis in strain K-0081, while this was not the case for K-0374. Yet, growth rate did explain the differences in prymnesin quota in the two strains. Consequently, the maximum prymnesin production rate (414 attomol cell-1 d-1) was only about three times higher in strain K-0081 than in K-0374, and revealed an optimum at the same irradiance of 200 µmol photons m-2 s-1 in both strains. At low irradiance levels, the difference in production rates between both strains became smaller, with 41 and 49 attomol cell-1 d-1 for K-0081 and K-0374, respectively. The carbon content of prymnesins made up for ∼3% and <1% of the total cellular carbon content in strains K-0081 and K-0374, respectively. The fraction of extracellular dissolved prymnesins was measured for strain K-0081, where it accounted for 14-30% of total prymnesin concentration in the cultures, irrespective of irradiance. The concentrations of prymnesins released to the water by the K-0081 strain were not significantly influenced by irradiance. Overall, we observed comparable responses in growth and photosynthesis of both tested strains toward changes in irradiance. However, the effects of irradiance on prymnesin quota and production rates were remarkably different between the two strains.

Update of the Planktonic Diatom Genus Pseudo-nitzschia in Aotearoa New Zealand Coastal Waters: Genetic Diversity and Toxin Production

Domoic acid (DA) is produced by almost half of the species belonging to the diatom genus Pseudo-nitzschia and causes amnesic shellfish poisoning (ASP). It is, therefore, important to investigate the diversity and toxin production of Pseudo-nitzschia species for ASP risk assessments. Between 2018 and 2020, seawater samples were collected from various sites around Aotearoa New Zealand, and 130 clonal isolates of Pseudo-nitzschia were established. Molecular phylogenetic analysis of partial large subunit ribosomal DNA and/or internal transcribed spacer regions revealed that the isolates were divided into 14 species (Pseudo-nitzschia americana, Pseudo-nitzschia arenysensis, Pseudo-nitzschia australis, Pseudo-nitzschia calliantha, Pseudo-nitzschia cuspidata, Pseudo-nitzschia delicatissima, Pseudo-nitzschia fraudulenta, Pseudo-nitzschia galaxiae, Pseudo-nitzschia hasleana, Pseudo-nitzschia multiseries, Pseudo-nitzschia multistriata, Pseudo-nitzschia plurisecta, Pseudo-nitzschia pungens, and Pseudo-nitzschia cf. subpacifica). The P. delicatissima and P. hasleana strains were further divided into two clades/subclades (I and II). Liquid chromatography-tandem mass spectrometry was used to assess the production of DA and DA isomers by 73 representative strains. The analyses revealed that two (P. australis and P. multiseries) of the 14 species produced DA as a primary analogue, along with several DA isomers. This study is the first geographical distribution record of P. arenysensis, P.cuspidata, P. galaxiae, and P. hasleana in New Zealand coastal waters.

First report of Alexandrium (Dinophyceae) associated with marine macroalgae off Japan: Diversity, distribution, and toxicity

Macroalgal samples were collected from coastal waters in subboreal to subtropical zones in Japan (< 3-30 m depths) and 32 clonal strains of non-motile dinoflagellate-like protists were established. Molecular phylogenetic analyses of the LSU rDNA D1/D2, SSU rDNA, ITS region, and concatenated SSU rDNA + LSU rDNA D1/D2 sequences revealed that the strains nested within the genus Alexandrium. They were separated into three novel phylotypes: Alexandrium spp. type 1, type 2, and type 3. Analysis of the concatenated sequences revealed that the most closely related species for the three phylotypes was A. ostenfeldii. Most cells from strains of the three phylotypes were non-motile and hemispherical to spherical in shape. The average diameters of the non-motile cells were between 35 and 39 µm. Type 1 and type 2 were widely distributed in Japan from the temperate to subtropical zones, whereas type 3 was restricted to the temperate zone. Furthermore, type 2 was widespread from shallow to deep waters, whereas type 1 and type 3 were restricted to deep waters. Growth experiments in strains belonging to the three phylotypes revealed that the occurrence ratios of motile cells were very low (≤ 1.1% of the total cells). The production of paralytic shellfish poisoning toxins, tetrodotoxin, and cyclic imines was assessed in strains belonging to the three phylotypes by LC/MS/MS analysis. The strains did not produce any of the toxins tested. The strains of the three phylotypes showed lethal toxicity to mice by intraperitoneal administration. To the best of our knowledge, this is the first study to report the existence of Alexandrium associated with marine macroalgae from Japan.

Taxonomy and okadaic acid production of a strain of Prorocentrum lima (Dinophyceae) isolated from the Bay of Bengal, North Indian Ocean

Prorocentrum lima (CSIRCSMCRI005) was isolated from the coastal seawater of Thonithurai, Tamil Nadu, India. Morphology of the isolate was studied using light microscopy (LM) and scanning electron microscopy (SEM) while phylogenetic analyses of the internal transcribed spacer region (ITS1-5.8s-ITS2), 18S rDNA, and large subunit (LSU) rDNA were also carried out. Growth of the isolate was studied, and okadaic acid (OA) production was examined using liquid chromatography with electrospray ionization and quadrupole time of flight mass spectroscopy (LC-ESI-Q-ToF-MS). Morphological features observed including oval cell shape with a broad middle region, narrow anterior and round posterior end, large central pyrenoid with starch sheath, smooth thecal surface, and V-shaped periflagellar area consisting of eight platelets matched with the description of the type species and those reported elsewhere. The ITS, 18S, and LSU sequence phylogenetic analysis revealed that the isolate was closely related to other strains reported from the pacific. The growth rate (μ) was 0.05 div. day^-1. P. lima CSIRCSMCRI005 produced okadaic acid and related esters. The production of free and total OA was 20.12 ± 4.77 and 22.30 fg cell^-1, respectively. The findings of this study contribute useful information concerning the regional risk of diarrheic shellfish poisoning in the North East Indian Ocean and the global distribution and toxic potential of Prorocentrum lima. Further studies on the ecophysiology of this strain will be helpful. This manuscript reports the detailed morphological, phylogenetic, and toxicological characterization of this species from the Bay of Bengal and the North Indian Ocean as a whole.

Ostreopsis lenticularis Y. Fukuyo (Dinophyceae, Gonyaulacales) from the South Atlantic Ocean: morphological and molecular characterization

Ostreopsis is a benthic dinoflagellate genus comprising eleven species including seven that are toxigenic. Ostreopsis lenticularis was first described from French Polynesia and is widely distributed in many insular locations from the Pacific Ocean. The current study presents morphological and molecular evidence of the presence of O. lenticularis at the Fernando de Noronha Archipelago, South Atlantic. Light microscopy and scanning electron microscopy of field cells showed morphological features in agreement with the description of O. lenticularis. Cells were broadly oval, 66.0-117.5 μm in dorso-ventral diameter, 50.0-92.5 μm in width, with thecal plates presenting two kinds of pores. Phylogenetic analyses based on LSU (D1-D3) and ITS sequences from field cells from Fernando de Noronha clustered with O. lenticularis sequences from elsewhere. The species was present in low to high abundances. The current study expands the distribution of O. lenticularis to Fernando de Noronha Archipelago in the South Atlantic Ocean.

Abundance of the benthic dinoflagellate Prorocentrum and the diversity, distribution, and diarrhetic shellfish toxin production of Prorocentrum lima complex and P. caipirignum in Japan

In the present study, the abundance of Prorocentrum and the molecular phylogeny, distribution, and DST production of P. lima complex and P. caipirignum in Japan were investigated. First, the cell densities of Prorocentrum were assessed from the temperate to subtropical zones in Japan between 2014 and 2018. The cell density in the subtropical zone [19.0 ± 40.2 cells/g wet weight (ww) algae] was significantly higher than that in the temperate zone (1.4 ± 3.4 cells/g ww algae). A total of 244 clonal strains were established from the temperate and subtropical zones. Phylogenetic analyses based on the large-subunit ribosomal DNA D1/D2 revealed that the strains were separated into four species/species complex/phylotypes (P. lima complex, P. caipirignum, and new phylotypes Prorocentrum spp. types 1 and 2). The strains of P. lima complex could be separated into two clades (1 and 3). Furthermore, the strains of clades 1 and 3 could be separated into nine subclades (1a, 1c, 1d, 1e, 1f, 1g, 1h, 1i, and 1j) and three subclades (3a, 3b, and 3c), respectively. The strains of P. caipirignum were separated into two subclades (b and e). Each phylotype/subclade showed a unique distribution pattern in Japan: P. lima complex subclades 1a, 1c, and 3a and P. caipirignum subclades b and e were widespread from the temperate to subtropical zones. On the other hand, P. lima complex subclades 1e and 1i were restricted to the temperate zone, and P. lima complex subclades 1d, 1f, 1g, 1h, 1j, 3b, and 3c and Prorocentrum spp. types 1 and 2 were restricted to the subtropical zone. Furthermore, the DST production of the 243 clonal strains was assessed by LC/MS/MS analysis. The results revealed that all strains produced okadaic acid (OA) and that the OA contents of P. lima complex subclades 1d and 1f, P. caipirignum subclades b and e, and Prorocentrum sp. type 2 tended to be higher than those of the other subclades. While P. lima complex subclades 1a, 1e, 1f, and 1i produced DTX1, the other phylotype/subclades produced either no or low quantities of DTX1. A strain of P. lima complex subclade 1e showed the highest OA and DTX1 contents (55.27 and 70.73 pg/cell, respectively) in the world. These results suggest that there are potential risks for DST accumulation in benthic animals in Japan.

A new diatom species P. hallegraeffii sp. nov. belonging to the toxic genus Pseudo-nitzschia (Bacillariophyceae) from the East Australian Current

A new species belonging to the toxin producing diatom genus Pseudo-nitzschia, P. hallegraeffii sp. nov., is delineated and described from the East Australian Current (EAC). Clonal cultures were established by single cell isolation from phytoplankton net hauls collected as part of a research expedition in the EAC region in 2016 on the RV Investigator. Cultures were assessed for their morphological and genetic characteristics, their sexual compatibility with other Pseudo-nitzschia species, and their ability to produce domoic acid. Light and transmission electron microscopy revealed cells which differed from their closest relatives by their cell width, rows of poroids, girdle band structure and density of band straie. Phylogenetic analyses based on sequencing of nuclear-encoded ribosomal deoxyribonucleic acid (rDNA) regions showed this novel genotype clustered within the P. delicatissima complex, but formed a discrete clade from its closest relatives P. dolorosa, P. simulans, P. micropora and P. delicatissima. Complementary base changes (CBCs) were observed in the secondary structure of the 3’ nuclear ribosomal transcribed spacer sequence region (ITS2) between P. hallegraeffii sp. nov. and its closest related taxa, P. simulans and P. dolorosa. Under laboratory conditions, and in the absence of any zooplankton cues, strains of P. hallegraeffii sp. nov. did not produce domoic acid (DA) and were not sexually compatible with any other Pseudo-nitzschia clones tested. A total of 18 Pseudo-nitzschia species, including three confirmed toxigenic species (P. cuspidata, P. multistriata and P. australis) have now been unequivocally confirmed from eastern Australia.

Sandwich hybridization probes for the detection of Pseudo-nitzschia (Bacillariophyceae) species: An update to existing probes and a description of new probes

New sandwich hybridization assay (SHA) probes for detecting Pseudo-nitzschia species (P. arenysensis, P. fraudulenta, P. hasleana, P. pungens) are presented, along with updated cross-reactivity information on historical probes (SHA and FISH; fluorescence in situ hybridization) targeting P. australis and P. multiseries. Pseudo-nitzschia species are a cosmopolitan group of diatoms that produce varying levels of domoic acid (DA), a neurotoxin that can accumulate in finfish and shellfish and transfer throughout the food web. Consumption of infected food sources can lead to illness in humans (amnesic shellfish poisoning; ASP) and marine wildlife (domoic acid poisoning; DAP). The threat of human illness, along with economic loss from fishery closures has resulted in the implementation of monitoring protocols and intensive ecological studies. SHA probes have been instrumental in some of these efforts, as the technique performs well in complex heterogeneous sample matrices and has been adapted to benchtop and deployable (Environmental Sample Processor) platforms. The expanded probe set will enhance future efforts towards understanding spatial, temporal and successional patterns in species during bloom and non-bloom periods.

Insights into the harmful algal flora in northwestern Mediterranean coastal lagoons revealed by pyrosequencing metabarcodes of the 28S rRNA gene

This study investigated the genetic diversity of phytoplankton communities in six shallow lagoons located on the French coast of the northwestern Mediterranean Sea that represented a trophic gradient ranging from oligotrophic to hypereutrophic. The phytoplankton communities were sampled once a month from spring (May) to the beginning of autumn (September/early October) in 2012 and fractionated by size. Metabarcodes were generated from cDNAs by targeting the D1-D2 region of the 28S rRNA gene and pyrosequenced using Roche 454 technology. Examination of the annotated barcodes revealed harmful algal species not previously documented in these lagoons. Three ichthyotoxic species belonging to Pfiesteriaceae were detected: Luciella masanensis was relatively widespread and abundant in many samples, whereas Pfiesteria piscicida and Stoeckeria changwonensis were found as single barcode sequences. Furthermore, a phylogenetic analysis of barcodes annotated as belonging to Pfiesteriaceae suggested the existence of two previously undescribed clades. The other toxic or potentially harmful dinoflagellates detected through rare barcodes were Dinophysis acuminata, Vulcanodinium rugosum, Alexandrium andersonii and A. ostenfeldii. The two most abundant dinoflagellate taxa were Gymnodinium litoralis and Akashiwo sanguinea with respect to sequence numbers. Four diatom species from the genus Pseudo-nitzschia that potentially produce domoic acid were identified (P. galaxiae, P. delicatissima, P. brasiliana and P. calliantha). These observations are discussed in terms of the literature and monitoring records related to the identified taxa in this Mediterranean area.

Recovery and identification of Pseudo-nitzschia (Bacillariophyceae) frustules from natural samples acquired using the environmental sample processor

Many species within the diatom genus Pseudo-nitzschia are difficult to distinguish without applying molecular analytical or microscopy-based methods. DNA, antibody and lectin probes have previously been used to provide rapid and specific detection of species and strains in complex field assemblages. Recently, however, well-documented cryptic genetic diversity within the group has confounded results of DNA probe tests in particular. Moreover, the number of species descriptions within the genus continues to increase, as do insights into toxin production by both new and previously described species. Therefore, a combination of classical morphological techniques and modern molecular methodologies is needed to resolve ecophysiological traits of Pseudo-nitzschia species. Here, we present an approach to recover and identify frustules from sample collection filters used for toxin analysis onboard the Environmental Sample Processor (ESP), an in situ sample collection and analytical platform. This approach provides a new and powerful tool for correlating species presence with toxin detected remotely and in situ by the ESP, and has the potential to be applied broadly to other sampling configurations. This new technique will contribute to a better understanding of naturally occurring Pseudo-nitzschia community structure with respect to observed domoic acid outbreaks.

Approaches for the detection of harmful algal blooms using oligonucleotide interactions

Blooms of microscopic algae in our waterways are becoming an increasingly important environmental concern. Many are sources of harmful biotoxins that can lead to death in humans, marine life and birds. Additionally, their biomass can cause damage to ecosystems such as oxygen depletion, displacement of species and habitat alteration. Globally, the number and frequency of harmful algal blooms has increased over the last few decades, and monitoring and detection strategies have become essential for managing these events. This review discusses developments in the use of oligonucleotide-based 'molecular probes' for the selective monitoring of algal cell numbers. Specifically, hybridisation techniques will be a focus.

Diversity and toxicity of the diatom Pseudo-nitzschia Peragallo in the Gulf of Maine, Northwestern Atlantic Ocean

Multiple species in the toxic marine diatom genus Pseudo-nitzschia have been identified in the Northwestern Atlantic region encompassing the Gulf of Maine (GOM), including the Bay of Fundy (BOF). To gain further knowledge of the taxonomic composition and toxicity of species in this region, Pseudo-nitzschia isolates (n=146) were isolated from samples collected during research cruises that provided broad spatial coverage across the GOM and the southern New England shelf, herein referred to as the GOM region, during 2007-2008. Isolates, and cells in field material collected at 38 stations, were identified using electron microscopy (EM). Eight species (P. americana, P. fraudulenta, P. subpacifica, P. heimii, P. pungens, P. seriata, P. delicatissima and P. turgidula), and a novel form, Pseudo-nitzschia sp. GOM, were identified. Species identity was confirmed by sequencing the large subunit of the ribosomal rDNA (28S) and the internal transcribed spacer 2 (ITS2) for six species (36 isolates). Phylogenetic analyses (including neighbor joining, maximum parsimony, and maximum likelihood estimates and ITS2 secondary structure analysis) and morphometric data supported the placement of P. sp. GOM in a novel clade that includes morphologically and genetically similar isolates from Australia and Spain and is genetically most similar to P. pseudodelicatissima and P. cuspidata. Seven species (46 isolates) were grown in nutrient-replete batch culture and aliquots consisting of cells and growth medium were screened by Biosense ASP ELISA to measure total domoic acid (DA) produced (intracellular + extracellular); P. americana and P. heimii were excluded from all toxin analyses as they did not persist in culture long enough for testing. All 46 isolates screened produced DA in culture and total DA varied among species (e.g., 0.04 to 320 ng ml^-1 for P. pungens and P. sp. GOM isolates, respectively) and among isolates of the same species (e.g., 0.24 - 320 ng ml^-1 for P. sp. GOM). The 15 most toxic isolates corresponded to P. seriata, P. sp. GOM and P. pungens, and fg DA cell^-1 was determined for whole cultures (cells and medium) using ELISA and liquid chromatography (LC) with fluorescence detection (FLD); for seven isolates, toxin levels were also estimated using LC - with mass spectrometry and ultraviolet absorbance detection. Pseudo-nitzschia seriata was the most toxic species (up to 3,500 fg cell^-1) and was observed in the GOM region during all cruises (i.e., during the months of April, May, June and October). Pseudo-nitzschia sp. GOM, observed only during September and October 2007, was less toxic (19 - 380 fg cell^-1) than P. seriata but more toxic than P. pungens var. pungens (0. 4 fg cell^-1). Quantitation of DA indicated that concentrations measured by LC and ELISA were positively and significantly correlated; the lower detection limit of the ELISA permitted quantification of toxicity in isolates that were found to be nontoxic with LC methods. The confirmation of at least seven toxic species and the broad spatial and temporal distribution of toxic Pseudo-nitzschia spp. have significant implications for the regional management of nearshore and offshore shellfisheries resources.

Specificity of lipoxygenase pathways supports species delineation in the marine diatom genus Pseudo-nitzschia

Oxylipins are low-molecular weight secondary metabolites derived from the incorporation of oxygen into the carbon chains of polyunsaturated fatty acids (PUFAs). Oxylipins are produced in many prokaryotic and eukaryotic lineages where they are involved in a broad spectrum of actions spanning from stress and defense responses, regulation of growth and development, signaling, and innate immunity. We explored the diversity in oxylipin patterns in the marine planktonic diatom Pseudo-nitzschia. This genus includes several species only distinguishable with the aid of molecular markers. Oxylipin profiles of cultured strains were obtained by reverse phase column on a liquid chromatograph equipped with UV photodiode detector and q-ToF mass spectrometer. Lipoxygenase compounds were mapped on phylogenies of the genus Pseudo-nitzschia inferred from the nuclear encoded hyper-variable region of the LSU rDNA and the plastid encoded rbcL. Results showed that the genus Pseudo-nitzschia exhibits a rich and varied lipoxygenase metabolism of eicosapentaenoic acid (EPA), with a high level of specificity for oxylipin markers that generally corroborated the genotypic delineation, even among genetically closely related cryptic species. These results suggest that oxylipin profiles constitute additional identification tools for Pseudo-nitzschia species providing a functional support to species delineation obtained with molecular markers and morphological traits. The exploration of the diversity, patterns and plasticity of oxylipin production across diatom species and genera will also provide insights on the ecological functions of these secondary metabolites and on the selective pressures driving their diversification.

CYTOLOGICAL AND PHYLOGENETIC DIVERSITY IN FRESHWATER ESOPTRODINIUM/BERNARDINIUM SPECIES (DINOPHYCEAE)(1)

The genera Esoptrodinium Javornický and Bernardinium Chodat comprise freshwater, athecate dinoflagellates with an incomplete cingulum but differing reports regarding cingulum orientation and the presence of chloroplasts and an eyespot. To examine this reported diversity, six isolates were collected from different freshwater ponds and brought into clonal culture. The isolates were examined using LM to determine major cytological differences, and rDNA sequences were compared to determine relatedness and overall phylogenetic position within the dinoflagellates. All isolates were athecate with a left-oriented cingulum that did not fully encircle the cell, corresponding to the current taxonomic concept of Esoptrodinium. However, consistent cytological differences were observed among clonal isolates. Most isolates exhibited unambiguous pale green chloroplasts and a distinct bright-red eyespot located at the base of the longitudinal flagellum. However, one isolate had cryptic chloroplasts that were difficult to observe using LM, and another had an eyespot that was so reduced as to be almost undetectable. Another isolate lacked visible chloroplasts but did possess the characteristic eyespot. Nuclear rDNA phylogenies strongly supported a monophyletic Esoptrodinium clade containing all isolates from this study together with a previous sequence from Portugal, within the Tovelliaceae. Esoptrodinium subclades were largely correlated with cytological differences, and the data suggested that independent chloroplast and eyespot reduction and/or loss may have occurred within this taxon. Overall, the isolates encompassed the majority of cytological diversity reported in previous observations of Bernardinium/Esoptrodinium in field samples. Systematic issues with the current taxonomic distinction between Bernardinium and Esoptrodinium are discussed.

REPORT OF A BLOOM-FORMING DINOFLAGELLATE TAKAYAMAACROTROCHA FROM TROPICAL COASTAL WATERS OF SINGAPORE(1)

Four clonal cultures of the unarmored dinoflagellate Takayama acrotrocha (J. Larsen) de Salas, Bolch et Hallegraeff were established from Singapore coastal water on October 20, 2004, and January 1, 2007, for a HAB monitoring project. LM and SEM observations demonstrated that the isolates were not consistent with the other five species within this genus in position of nucleus, shape of the apical groove, and number and shape of chloroplasts. New morphological observations of the Singapore isolates that were not in the type description of T. acrotrocha include a narrow and shallow slit located above the entire anterior edge of the cingulum, a tube-like structure in the sulcus, numerous multilateral plate-like surface vesicles, a sulcal intrusion into the epicone, and possibly a peduncle in between the two emerging points of flagella. The presence of sulcal intrusion into the epicone was not consistent with the type description but is prominent in SEM micrographs. Phylogenetic analysis of the partial LSU rDNA sequences indicated Singapore strains of T. acrotrocha are conspecific with two isolates from Italy, but less homologous to T. helix, T. tasmanica, and T. tuberculata. Laboratory fish bioassays using Asian sea bass (Lates calcarifer) and sheepshead minnows (Cyprinodon variegates) did not indicate fish-killing activity by this species, and to our knowledge, there were no reports of fish-kills occurring during blooms of this species in Singapore and Italy. This is the first report of T. acrotrocha from tropical waters and indicates a likely cosmopolitan distribution of the species.

GENETIC VARIATION AMONG STRAINS OF PSEUDOPFIESTERIA SHUMWAYAE AND PFIESTERIA PISCICIDA (DINOPHYCEAE)(1)

The putatively toxic dinoflagellates Pseudopfiesteria shumwayae (Glasgow et J. M. Burkh.) Litaker, Steid., P. L. Mason, Shields et P. A. Tester and Pfiesteria piscicida Steid. et J. M. Burkh. have been implicated in massive fish kills and of having negative impacts on human health along the mid-Atlantic seaboard of the USA. Considerable debate still remains as to the mechanisms responsible for fish mortality (toxicity vs. micropredation) caused by these dinoflagellates. Genetic differences among these cultures have not been adequately investigated and may account for or correlate with phenotypic variability among strains within each species. Genetic variation among strains of Ps. shumwayae and P. piscicida was examined by PCR-RFLP analysis using cultures obtained from the Provasoli-Guillard National Center for Culture of Marine Phytoplankton (CCMP), as well as those from our own and other colleagues' collection efforts. Examination of restriction digest banding profiles for 22 strains of Ps. shumwayae revealed the presence of 10 polymorphic restriction endonuclease sites within the first and second internal transcribed spacers (ITS1 and ITS2) and the 5.8S gene of the rDNA complex, and the cytochrome oxidase subunit I (COI) gene. Three compound genotypes were represented within the 22 Ps. shumwayae strains. Conversely, PCR-RFLP examination of 14 strains of P. piscicida at the same ITS1, 5.8S, and ITS2 regions revealed only one variable restriction endonuclease site, located in the ITS1 region. In addition, a dinoflagellate culture listed as P. piscicida (CCMP 1928) and analyzed as part of this study was identified as closely related to Luciella masanensis P. L. Mason, H. J. Jeong, Litaker, Reece et Steid.

Presence of Alexandrium catenella and paralytic shellfish toxins in finfish, shellfish and rock crabs in Monterey Bay, California, USA

The central California coast is a highly productive, biodiverse region that is frequently affected by the toxin-producing dinoflagellate Alexandrium catenella. Despite the consistent presence of A. catenella along our coast, very little is known about the movement of its toxins through local marine food webs. In the present study, we investigated 13 species of commercial finfish and rock crabs harvested in Monterey Bay, California for the presence of paralytic shellfish toxins (PSTs) and compared them to the presence of A. catenella and PSTs in sentinel shellfish over a 3-year period. Between 2003 and 2005, A. catenella was noted in 55% of surface water samples (n = 307) and reached a maximum concentration of 17,387 cells L-1 at our nearshore site in Monterey Bay. Peak cell densities occurred in the month of July and were associated with elevated shellfish toxicity in the summers of 2004 and 2005. When A. catenella was present, particulate PSTs were detected 71% of the time and reached a maximum concentration of 962 ng STXeq L-1. Of the 13 species tested, we frequently detected PSTs in Pacific sardines (Sardinops sagax; maximum 250 μg STXeq 100 g-1), northern anchovies (Engraulis mordax; maximum 23.2 μg STXeq 100 g-1), brown rock crabs (Cancer antennarius; maximum 49.3 μg STXeq 100 g-1) and red rock crabs (C. productus; 23.8 μg STXeq 100 g-1). PSTs were also present in one sample of Pacific herring (Clupea pallas; 13.3 μg STXeq 100 g-1) and one sample of English sole (Pleuronectes vetulus; 4.5 μg STXeq 100 g-1), and not detected in seven other species of flatfish tested. The presence of PSTs in several of these organisms reveals that toxins produced by A. catenella are more prevalent in California food webs than previously thought and also indicates potential routes of toxin transfer to higher trophic levels.

STRAIN VARIATION IN KARLODINIUM VENEFICUM (DINOPHYCEAE): TOXIN PROFILES, PIGMENTS, AND GROWTH CHARACTERISTICS(1)

Karlodinium veneficum (D. Ballant.) J. Larsen strains, 16 from the U.S. Atlantic eastern seaboard and two from New Zealand (CAWD66 and CAWD83), were used to characterize toxin profiles during batch culture. All 18 strains were determined as the same species based on ITS sequence analyses, a positive signal in a chloroplast real-time PCR assay and pigment composition. Five karlotoxin 1 (KmTx 1) containing strains were analyzed from the Chesapeake Bay, and 10 karlotoxin 2 (KmTx 2) strains were analyzed from Florida to North Carolina. One strain (MD5) from the Chesapeake Bay produced no detectable toxin. The two cultures from New Zealand contained both novel karlotoxins with lower masses and earlier elution times. Toxin type did not change during batch culture, although the KmTx phenotype did change in some strains under extensive (months) phototrophic growth in replete media. KmTx cell quota did not change during batch culture for most strains. The mass spectrum for every KmTx examined showed a pattern of multiple coeluting congeners within each HPLC peak, with masses typically differing by 16 amu. KmTx congeners tested showed nearly a 500-fold range in specific hemolytic activity, with KmTx 1 (typically occurring at lower cellular levels) most hemolytic and CAWD66 toxin least hemolytic, while KmTx 2 and the CAWD83 toxin had similar intermediate specific activity. Despite morphological, genetic, and photopigment indicators consistent with species homogeneity among the 18 strains of K. veneficum, the high degree of toxin variability suggests different functional roles among strains that likely coexist in situ.

NOVEL UNARMORED DINOFLAGELLATES FROM THE TOXIGENIC FAMILY KARENIACEAE (GYMNODINIALES): FIVE NEW SPECIES OF KARLODINIUM AND ONE NEW TAKAYAMA FROM THE AUSTRALIAN SECTOR OF THE SOUTHERN OCEAN(1)

Six new species of unarmored dinoflagellates in the family Kareniaceae were isolated from the Australian sector of the Southern Ocean in March 2006: Takayama tuberculata de Salas sp. nov, Karlodinium antarcticum de Salas sp. nov., Karl. ballantinum de Salas sp. nov., Karl. conicum de Salas sp. nov., Karl. corrugatum de Salas sp. nov., and Karl. decipiens de Salas et Laza-Martínez sp. nov. These new taxa were characterized using light and electron microscopy and sequencing of the LSU rDNA and are well supported based either on their morphology or molecular phylogeny. Takayama tuberculata, isolated just north of the polar front (55°-57° S), is genetically close to T. tasmanica, but smaller, with a significantly reduced number of amphiesmal vesicles. Medium-sized Karl. antarcticum, also isolated from near the polar front, is characterized by its long ovoid cell outline and very long apical groove. The small Karl. ballantinum has a very short apical groove. The large Karl. conicum has a distinct conical epicone and spherical posterior nucleus. The small Karl. corrugatum, from just south of the polar front, has distinctive parallel striations on the epicone surface and a distinctively shaped and placed ventral pore. The large and widespread Karl. decipiens, distributed through Southern Ocean waters from the polar front to Tasmanian coastal waters, and coastal Spain, has a helicoidal chloroplast arrangement and a large central nucleus. This study represents the first description of species in the potentially ichthyotoxic family Kareniaceae recorded from the Southern Ocean.

Neurohistochemical biomarkers of the marine neurotoxicant, domoic acid

Domoic acid and its potent excitotoxic analogues glutamic acid and kainic acid, are synthesized by marine algae such as seaweed and phytoplankton. During an algal bloom, domoic acid may enter the food web through its consumption by a variety of marine organisms held in high regard as seafoods by both animals and humans. These seafoods include clams, mussels, oysters, anchovies, sardines, crabs, and scallops, among others. Animals, such as pelicans, cormorants, loons, grebes, sea otters, dolphins, and sea lions, which consume seafood contaminated with domoic acid, suffer disorientation and often death. Humans consuming contaminated seafood may suffer seizures, amnesia and also sometimes death. In addition to analytical measurement of domoic acid exposure levels in algae and/or seafood, it is useful to be able to identify the mode of toxicity through post-mortem evaluation of the intoxicated animal. In the present study, using the rat as an animal model of domoic acid intoxication, we compared histochemical staining of the limbic system and especially the hippocampus with degeneration-selective techniques (Fluoro-Jade and silver), a conventional Nissl stain for cytoplasm (Cresyl violet), a myelin-selective stain (Black-Gold), an astrocyte-specific stain (glial fibrillary acidic protein), early/immediate gene responses (c-Fos and c-Jun), as well as for heat shock protein (HSP-72) and blood-brain barrier integrity (rat IgG). The results demonstrate that the degeneration-selective stains are the biomarkers of domoic acid neurotoxicity that are the most useful and easy to discern when screening brain sections at low magnification. We also observed that an impairment of blood-brain barrier integrity within the piriform cortex accompanied the onset of domoic acid neurotoxicity.

Comparison of paralytic shellfish toxin (PST) production by the dinoflagellates Alexandrium lusitanicum NEPCC 253 and Alexandrium tamarense NEPCC 407 in the presence and absence of bacteria

The ability of two Alexandrium species to produce paralytic shellfish toxins (PST) in laboratory culture following the generation of bacteria-free cultures was investigated. The dinoflagellates Alexandrium lusitanicum NEPCC 253 and Alexandrium tamarense NEPCC 407 were cultured in the presence of antibiotics and tested for residual bacteria. After treatment with a cocktail of streptomycin, ciprofloxacin, gentamicin and penicillin G, bacteria could not be detected in either of the treated Alexandrium cultures using 17 different solid and broth bacterial growth media, by epifluorescence microscopy with the dye Sybr green 1, or polymerase chain reaction amplification using universal eubacterial primers designed to target the 16S rRNA gene. Subsequent analysis of A. lusitanicum for PST using high performance liquid chromatography demonstrated that the growth rate and toxin profile remained similar in both bacteria-free and control cultures, although the quantity of toxins produced differed with the bacteria-free culture producing generally more of each compound and also having a greater toxin content in terms of saxitoxin equivalents. A. tamarense also retained similarities between the bacteria-free and control cultures in terms of growth rates and toxin profile, although in this instance, depending on the growth stage and the toxin, the control culture produced more of some toxins than the bacteria-free culture. The control culture was also more toxic in terms of saxitoxin equivalents than the axenic culture. These results suggest that bacteria can influence toxin production in laboratory cultures of Alexandrium species although the mechanisms remain unknown.

Detection of stable pre-rRNA in toxigenic Pseudo-nitzschia species

Nucleotide sequence analysis of ribosomal DNA (rDNA) spacer regions is useful for taxonomic comparisons of closely related microorganisms. These regions have been less useful for routine microbial identification and detection, partly because rRNA precursors (pre-rRNAs) in microbial cells are assumed to be too labile to be detectable by high-throughput probe hybridization methods. We characterized the sequence diversity and physiological stability of pre-rRNA in the toxigenic marine diatoms Pseudo-nitzschia australis, P. multiseries, and P. pungens. As with nucleotide sequences of the first internal transcribed spacer (ITS1) reported previously, sequences of ITS2 and the 5' external transcribed spacer (ETS1) exhibited considerable divergence among these species, including large insertions-deletions detectable by PCR-based spacer length analysis. In slot blot hybridization assays on RNA extracted from lysates of Pseudo-nitzschia cells, oligonucleotide probes directed to pre-rRNA spacers generated much stronger signals than did complementary probes directed to the coding strands of the rDNAs, indicating that the pre-rRNA-targeted probes detected multicopy transcripts. A group of probes directed to a discrete 90-base region within the ITS1 pre-rRNA gave no detectable signal, suggesting that this region is degraded early in the rRNA maturation pathway. Other pre-rRNA regions were always detectable and, in marked contrast to prokaryotic systems analyzed in this manner, were stable and abundant in both actively dividing and nondividing cells. Long, multilabeled RNA probes, which would exhibit considerable cross-reactivity if directed to mature rRNA sequences, detected species-specific pre-rRNA sequences from as few as 1,000 cells. Pre-rRNA is a potentially useful molecular target for detecting and identifying Pseudo-nitzschia species and possibly other unicellular eukaryotes as well.

Domoic acid-producing diatom blooms in Monterey Bay, California: 1991-1993

During the autumn of 1991, numerous seabird fatalities in Monterey Bay, California, led to the discovery of a new domoic acid-producing diatom, Pseudonitzschia australis. Since this initial event, sizable populations of P. australis, as well as other likely toxin producers, P. pungens f. multiseries and P. pseudodelicatissima, have occurred biannually in Monterey Bay. Using the highly sensitive FMOC-HPLC method, we detected domoic acid whenever Pseudonitzschia australis was found in the plankton, even at densities as low as 4.0 x 10(3) cells/L. Based on correlations of domoic acid and P. australis abundances and the overwhelming biovolume dominance of P. australis, we conclude that P. australis has been the major domoic acid producer during the period of our study. Our study suggests that P. australis cells may always be toxic in natural populations and that toxin concentrations on a per cell basis have no statistically significant relationship to population density or to nutrient concentrations other than silicate. Cellular levels of domoic acid were positively correlated with silicate concentrations, which is at variance with reports from prior culture experiments. These conclusions must be tentative because of the limited extent of our sampling. Nevertheless, these preliminary data indicate that further investigations of environmental conditions affiliated with cell growth and toxin production in P. australis are warranted. As a practical matter, domoic acid in the pelagic environment cannot be reliably or consistently detected by monitoring domoic acid levels in intertidal mussels. Direct measurement of domoic acid using sensitive HPLC methods is probably the most cost-effective and accurate approach for an ongoing phycotoxin monitoring program.