Emiliania huxleyi (Lohmann) W. W. Hay et H. Mohler is a cosmopolitan coccolithophore occurring from tropical to subpolar waters and exhibiting variations in morphology of coccoliths possibly related to environmental conditions. We examined morphological characters of coccoliths and partial mitochondrial sequences of the cytochrome oxidase 1b (cox1b) through adenosine triphosphate synthase 4 (atp4) genes of 39 clonal E. huxleyi strains from the Atlantic and Pacific Oceans, Mediterranean Sea, and their adjacent seas. Based on the morphological study of culture strains by SEM, Type O, a new morphotype characterized by coccoliths with an open central area, was separated from existing morphotypes A, B, B/C, C, R, and var. corona, characterized by coccoliths with central area elements. Molecular phylogenetic studies revealed that E. huxleyi consists of at least two mitochondrial sequence groups with different temperature preferences/tolerances: a cool-water group occurring in subarctic North Atlantic and Pacific and a warm-water group occurring in the subtropical Atlantic and Pacific and in the Mediterranean Sea.

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We have developed a useful method to obtain light and scanning electron micrographs of a single dinoflagellate cell, prior to applying the cell to the single cell PCR technique. This method allows us to record detailed morphological information on any cell used for sequencing, which can be extremely important for the future identification of the organism, because cells used for single cell PCR usually cannot be retained. Furthermore, by applying multiple sets of PCR primers at the same time, we have successfully amplified and sequenced multiple genes (and DNA regions) simultaneously, even from a single cell. In this note, we demonstrate the methods of this technique by using two different types of dinoflagellates, i.e. an armored freshwater species, Peridinium willei Huitfeld-Kaas, and an unarmored marine species, Akashiwo sanguinea (Hirasaka) Hansen and Moestrup. By rotating the cell, photographs of all aspects of a single cell can be taken even using the SEM. The genes and DNA regions sequenced in these examples include a region of the ribosomal DNA (SSU, ITS1, 5.8S, ITS2, and part of the LSU) as well as part of the mitochondrial DNA-encoded gene, cox1. This technique can be applied to both photosynthetic and heterotrophic dinoflagellates and will accelerate biodiversity studies.

Small subunit rRNA gene sequences were determined for four unarmored heterotrophic dinoflagellates ( Gyrodinium spirale , the type species of the genus Gyrodinium , as well as G. fusiforme , Gymnodinium rubrum and the freshwater species G. helveticum ) using a single-cell polymerase chain reaction (PCR) technique. For identification and record keeping, each cell was carefully observed and photographed using a light microscope under high magnification, prior to singlecell PCR. G. rubrum and G. helveticum possess an elliptical apical groove and longitudinal striations similar to those of G. spirale and G. fusiforme , and molecular phylogenetic studies reveal that the four species form a single clade. We therefore propose the following new combinations: Gyrodinium rubrum (Kofoid et Swezy) Takano et Horiguchi comb. nov. and Gyrodinium helveticum (Penard) Takano et Horiguchi comb. nov.

In order to gain insight into the bloom sustainment of colonial Microcystis aeruginosa Kü tz., physiological characterizations were undertaken in this study. Compared with unicellular Microcystis, colonial Microcystis phenotypes exhibited a higher maximum photosynthetic rate (P m), a higher maximum electron transfer rate (ETR max), higher phycocyanin content, and a higher affinity for inorganic carbon (K 0.5 DIC # 8.4 6 0.7 mM) during the growth period monitored in this study. This suggests that photosynthetic efficiency is a dominant physiological adaptation found in colonial Microcystis, thus promoting bloom sustainment. In addition, the high content of soluble and total carbohydrates in colonial Microcystis suggests that this phenotype may possess a higher ability to tolerate enhanced stress conditions when compared to unicellular (noncolonial) phenotypes. Therefore, high photosynthetic activities and high tolerance abilities may explain the bloom sustainment of colonial Microcystis in eutrophic lakes.

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Partial SSU rDNA sequences were obtained from 13 naturally collected cells of Braarudosphaera bigelowii obtained from various parts of seas surrounding Japan.Together with the two previously reported sequences, 15 specimens were classified into five SSU rDNA Genotypes I-V. Based on the side length of the pentaliths forming the coccosphere, these specimens were also classified into three size-morphotypes;

The nuclear 18S-rRNA gene has been used as a metabarcoding marker in massively parallel sequencing (MPS)-based environmental surveys for plankton biodiversity research. However, different hypervariable regions have been used in different studies, and their utility has been debated among researchers. In this study, detailed investigations into 18S-rRNA were carried out; we investigated the effective number of sequences deposited in international nucleotide sequence databases (INSDs), the amplification bias, and the amplicon sequence variability among the three variable regions, V1-3, V4-5 and V7-9, using in silico polymerase chain reaction (PCR) amplification based on INSDs. We also examined the primer universality and the taxonomic identification power, using MPS-based environmental surveys in the Sea of Okhotsk, to determine which region is more useful for MPS-based monitoring. The primer universality was not significantly different among the three regions, but the number of sequences deposited in INSDs was markedly larger for the V4-5 region than for the other two regions. The sequence variability was significantly different, with the highest variability in the V1-3 region, followed by the V7-9 region, and the lowest variability in the V4-5 region. The results of the MPS-based environmental surveys showed significantly higher identification power in the V1-3 and V7-9 regions than in the V4-5 region, but no significant difference was detected between the V1-3 and V7-9 regions. We therefore conclude that the V1-3 region will be the most suitable for future MPS-based monitoring of natural eukaryote communities, as the number of sequences deposited in INSDs increases.