Bispinodinium angelaceum gen. et sp. nov. (Dinophyceae), a new sand-dwelling dinoflagellate from the seafloor off Mageshima Island, Japan(1)

Diversity and toxicity of Pacific strains of the benthic dinoflagellate Coolia (Dinophyceae), with a look at the Coolia canariensis species complex

Coolia Meunier 1919 from benthic assemblages of Hawai'i and Guam were isolated and clonal cultures were established from single cells. Cultures were identified to species-level based on 28S rRNA and ITS-5.8S rRNA genes and tested for toxicity. In Hawai'i, two strains of C. malayensis were isolated. In Guam, a high biodiversity was identified: four strains of C. malayensis, one strain of C. palmyrensis, one strain of C. tropicalis, one strain of C. canariensis phylogroup III, and two strains forming a new phylogroup (phylogroup IV) of nontoxic C. canariensis. Morphology of the new C. canariensis phylogroup was described using light microscopy and scanning electron microscopy. Mass cultures and methanol extracts of representative cultures (C. malayensis, C. palmyrensis, C. canariensis, C. tropicalis) from Guam were prepared for liquid chromatography-mass spectrometry analysis. Chemical analyses revealed yessotoxin analogue C₅₆H₇₈O₁₈S₂ is produced by C. malayensis, C. canariensis phylogroup IV and C. palmyrensis, but other analogues, C₅₇H₈₀O₁₈S₂ and C₅₈H₈₆O₁₈S₂, were only found in C. malayensis (Okinawa) and C. canariensis phylogroup IV. Individual toxin profiles were also different over time for an Okinawa strain of C. malayensis (NIES-3637), highlighting intra and inter-species variation in Yessotoxin-analogue expression. Biological activity was tested using Artemia bioassay and toxicity was observed in Guam and Okinawa strains of C. malayensis. Strong support of four distinct clades within the C. canariensis species complex was recovered in phylogenetic analyses, despite morphological similarities.

Morphology and Molecular Phylogeny of a New Marine, Sand-dwelling Dinoflagellate Genus, Pachena (Dinophyceae), with Descriptions of Three New Species

Marine benthic dinoflagellates are interesting not only because some epiphytic genera can cause harmful algal blooms but also for understanding dinoflagellate evolution and diversification. Our understanding of their biodiversity is far from complete, and many thecate genera have unusual tabulation patterns that are difficult to relate to the diverse known phytoplankton taxa. A new sand-dwelling genus, Pachena gen. nov., is described based on morphological and DNA sequence data. Three species were discovered in distant locations and are circumscribed, namely, P. leibnizii sp. nov. from Canada, P. abriliae sp. nov. from Spain, and P. meriddae sp. nov. from Italy. All species are tiny (about 9-23 μm long) and heterotrophic. Species are characterized by their tabulation (APC 4' 3a 6'' 5c 5s 5''' 2''''), an apical hook covering the apical pore, an ascending cingulum, and a sulcus with central list. The first anterior intercalary plate is uniquely "sandwiched" between two plates. The species share these features and differ in the relative sizes and arrangements of their plates, especially on the epitheca. The ornamentation of thecal plates is species-specific. The new molecular phylogenies based on SSU and LSU rDNA sequences contribute to understanding the evolution of the planktonic relatives of Pachena, the Thoracosphaeraceae.

On the extrusomes of Oxyrrhis marina (Dinophyceae)

Oxyrrhis marina was subjected to conventional transmission electron microscopy, with emphasis being laid on its extrusomes. Mainly regular trichocysts were obvious in ultrathin sections. They were highly abundant, approximately 2 μm in length and 200 nm in width, and composed of the characteristic features, i.e., an anterior tip and the posterior crystalline body. The tip measures approximately 440 nm in length and is built by an outer less electron-dense concentric layer followed by an inner electron-dense core with a translucent center in the middle. The less electron-dense layer most likely ends up in a bundle of filaments which are concentrically placed around the electron-dense core in the transition zone between the tip and body. Trichocyst bodies which are sectioned along the longitudinal axis are approximately 1.5 μm in length and show a regular striation of electron-dense and electron-translucent lines with a spacing of 9 nm. Cross-sectioned bodies are square-shaped and show a crystalline lattice composed of particles which are 8-9 nm in size. Discharge of regular trichocysts results in long rigid rods. They are square-shaped, 54 nm broad, and with a regular striation of approximately 54 nm along their longitudinal axes. Besides regular trichocysts, an additional type of extrusome was registered. It is not as abundant as regular trichocysts, membrane-enclosed, 2 μm in length and 180 nm in width, and resembles two bullets adjacent to each other with the tips facing in opposite directions. The two parts are slightly of different lengths (anterior part, 740 nm; posterior part, 590 nm) and widths (anterior part, 126 nm; posterior part, 117 nm) and separated from each other by a gap of 30 nm. The anterior part is more electron-dense than the posterior one. A faint electron-dense sheet-like structure was registered between the envelope membrane and these two inner structures. In extrusomes which had been arrested in the process of discharge, the anterior part gives rise to an oozing, amorphous, fibrous blob, while the posterior part consists of twisted filaments which most likely function as the charge of a gun for the release of the anterior part.

Pigment compositions are linked to the habitat types in dinoflagellates

Compared to planktonic species, there is little known about the ecology, physiology, and existence of benthic dinoflagellates living in sandy beach or seafloor environments. In a previous study, we discovered 13(2),17(3)-cyclopheophorbide a enol (cPPB-aE) from sand-dwelling benthic dinoflagellates. This enol had never been detected in phytoplankton despite the fact that it is a chlorophyll a catabolite. We speculated from this discovery that habitat selection might be linked to pigment compositions in dinoflagellates. To test the hypothesis of habitat selection linking to pigment compositions, we conducted extensive analysis of pigments with high performance liquid chromatography (HPLC) for 40 species using 45 strains of dinoflagellates including three habitat types; sand-dwelling benthic forms, tidal pool inhabitants and planktonic species. The 40 dinoflagellates are also able to be distinguished into two types based on their chloroplast origins; red alga-derived secondary chloroplasts and diatom-derived tertiary ones. By plotting the pigments profiles onto three habitats, we noticed that twelve pigments including cPPB-aE were found to occur only in benthic sand-dwelling species of red alga-derived type. The similar tendency was also observed in dinoflagellates with diatom-derived chloroplasts, i.e. additional sixteen pigments including chl c 3 were found only in sand-dwelling forms. This is the first report of the occurrence of chl c 3 in dinoflagellates with diatom-derived chloroplasts. These results clarify that far greater diversity of pigments are produced by the dinoflagellates living in sand regardless of chloroplast types relative to those of planktonic and tidal pool forms. Dinoflagellates seem to produce a part of their pigments in response to their habitats.

Isolation and characterisation of the trichocysts of the dinophyte Prorocentrum micans

Trichocyst-enriched fractions were isolated from the marine dinophyte Prorocentrum micans. Transmission electron microscopy revealed that most of the trichocysts were discharged and had elongated to long filaments. Some trichocysts were still condensed. Fragments of discharged trichocysts measured up to 20 μm in length and 260 nm in width, those still condensed measured up to 1 μm in width and 16 μm in length. A distinct banding pattern with a transversal periodicity of approximately 16-18 nm and a periodic longitudinal striation of 3-4 nm could be measured along the trichocyst filaments. At higher magnifications, a fragile, alveolated, net-like organisation became obvious which resembled the one shown for the trichocysts of ciliates. When trichocyst-enriched fractions were treated with sodium dodecyl sulfate and centrifuged subsequently, no trichocysts were registered any longer in the sodium dodecyl sulfate-insoluble fraction by electron microscopy. Sodium dodecyl sulfate polyacrylamide gel electrophoresis of trichocyst-enriched fractions and of the SDS-soluble fractions revealed a protein banding pattern which was dominated by polypeptides of 50-30, 12.5, and approximately 8.5 kDa. The polypeptide banding pattern deviated significantly from those registered for ejectisomes of cryptophytes and of the prasinophyte Pyramimonas grossii, for the Reb polypeptides which constitute the R-bodies of Caedibacter taeniospiralis, and also from the banding pattern of trichocysts of Paramecium. An antiserum directed against trichocysts of Paramecium did not cross-react with the polypeptides present in the trichocyst-enriched fraction of Prorocentrum micans.

cPPB-aE is discovered from photosynthetic benthic dinoflagellates

Although chlorophyll degradation pathways in higher plants have been well studied, little is known about the mechanisms of chlorophyll degradation in microalgae. In this article, we report the occurrence of a chlorophyll a derivative that has never been discovered in photosynthetic organisms. This chlorophyll derivative emits no fluorescence and has a peculiar absorbance peak at 425, 451, 625, and 685 nm. From these features, it was identified as 13(2) ,17(3) -cyclopheophorbide a enol (cPPB-aE), reported as a degradation product of chlorophyll a derived from prey algal cells in heterotrophic protists. We discovered cPPB-aE in six benthic photosynthetic dinoflagellates that are phylogenetically separated into four clades based on SSU rDNA molecular phylogeny. This is the first report of this chlorophyll derivative in photosynthetic organisms and we suggest that the derivative is used to quench excess light energy.