Search

The red tide forming heterotrophic dinoflagellate Noctiluca scintillans is common in temperate to tropical waters around the world. Understanding the in situ prey of N. scintillans is essential for elucidating its role in marine microbial food webs. In this study, we applied two polymerase chain reaction (PCR)-based cloning techniques, a predator-specific restriction enzyme, and a blocking primer. The PCR of nuclear 18S rDNA was performed on single N. scintillans cells that were collected from Ishinomaki Bay, Japan, in May 2018. The maximum detection rates of non-Noctiluca sequences were 56% using the restriction enzyme method and 87% with the blocking primer method, representing a broad taxonomic range of organisms, including diatom, dinoflagellate, bolidophyte, haptophyte, euglenophyte, green algae, golden algae, ciliate, heliozoa, copepod, brown seaweed, sponge, bivalve, and polychaete. The diverse DNA was probably ingested by N. scintillans directly or indirectly through secondary predation or ingestion of marine snow or detritus containing many organisms. The application of molecular approaches to various species may reveal undiscovered interactions within the phytoplankton community, including prey-predator, or symbiotic relationships.

To determine the process of population expansion and ascertain the origin of the Sea of Japan population, in a noxious red tide forming dinoflagellate Cochlodinium polykrikoides, 13 samples, isolated from 11 different localities in Japanese and Korean coasts, were analysed using 10 polymorphic microsatellites. Analyses by nonmetric multidimensional scaling plots of pairwise F(ST), global amova, and genetic admixture analysis identified three clusters--the Sea of Japan populations, Yatsushiro Sea (Kumamoto Pref.) populations, and other populations--indicating genetic structuring of the 13 samples into three distinct populations. In the proportion of shared alleles by pairwise individuals (P(SAxy)) analyses between the Sea of Japan and the other samples, P(SAxy) was extremely low compared with that among the Sea of Japan or among other samples, indicating that a large genetic barrier has occurred between the populations. No significant relationship of isolation-by-distance patterns and almost no genetic distance were detected between pairwise samples of the Sea of Japan, although there is a maximal distance of600 km between samples. In addition, P(SAxy) data among the samples were extremely high compared with those among other samples, clearly showing that a large-scale transfer from west to east has occurred via the Tushima Warm Current. In the P(SAxy) data of the Seto Inland Sea and Pacific samples, individuals showing relatively high P(SAxy) were concentrated in the three areas of Nagasaki, Harima, and Mie, suggesting that frequent transfer may have occurred by human-assisted dispersal, although Nagasaki and Mie are separated by a distance of approximately 700 km.

S. Nagai, G. Nishitani, Y. Takano, M. Yoshida and H. Takayama. 2009. Encystment and excystment under laboratory conditions of the nontoxic dinoflagellate Alexandrium fraterculus (Dinophyceae) isolated from the Seto Inland Sea, Japan. Phycologia 48: 177–185. DOI: 10.2216/08-43.1. The sexuality (i.e. encystment and excystment) of the nontoxic dinoflagellate Alexandrium fraterculus, isolated from the Seto Inland Sea, Japan, was clarified for the first time under laboratory conditions. Sexual reproduction was by conjugation of isogametes, and plasmogamy was completed in 25–60 min after the conjugation started and produced a planozygote with one transverse and two longitudinal flagella, then a cyst was formed. Cysts were round or elliptical. The cyst size was 37.5–50.0 µm in diameter. The surface of cysts was smooth, and there was no paratabulation. Encystment through sexual reproduction was observed in two of 28 pairs, which included seven self-crossings, by use of seven nonaxenic clonal strains. No ...

We report the successful growth of the toxic dinoflagellate Dinophysis infundibulus under laboratory conditions, when fed the marine ciliate Myrionecta rubra grown with the cryptophyte Teleaulax amphioxeia; this study follows previous studies on D. acuminata, D. caudata, and D. fortii, showing the mixotrophy. We succeeded in maintaining several clonal strains of D. infundibulus for a relatively long period of time (> 8 mol. Growth rates in D. infundibulus ranged from 0.40 to 0.94 divisions d -1 , reaching a maximum concentration of 1.2 to 2.3 x 10 3 cells ml -1 . The rate was 0.36 divisions d -1 when apparently fully expanded cells, resulting from the active ingestion of Myrionecta rubra, were cultivated without the ciliate prey. In contrast, the culture of D. infundibulus was not established in the absence of the ciliate or when provided only with the cryptophyte T. amphioxeia, suggesting that D. infundibulus cannot directly use T. amphioxeia as prey. We also determined the sequences of nuclear small subunit (SSU) rRNA, 5.8S rRNA with internal transcribed spacers (ITS1 and ITS2), and large subunit (LSU) rRNA regions in D. infundibulus. Phylogenetic relationships revealed that they are non-identical with regard to any of the DNA sequence data of Dinophysis deposited in GenBank, and are distinguishable from other Dinophysis species for species identification.

Recently, Park et al. (2006) succeeded in cultivating the toxic dinoflagellate Dinophysis acuminata and maintaining them by feeding the ciliate Myrionecta rubra grown with a cryptophyte Teleaulax sp. After this report, the present study is the second report of propagation of a Dinophysis species (Dinophysis caudata) under laboratory condi- tions and describes the maintenance of several clonal strains kept at high abundance (� 5,000 cells mL � 1 ) for a rela- tively long period (� 4 months) when fed on M. rubra with the addition of Teleaulax amphioxeia. We confirmed that D. caudata swam actively around its ciliate prey and inserted its peduncle (feeding tube) into the ciliate. Thereafter, the prey became immobile and rounded. Dinophysis caudata actively ingested the cytoplasm of the prey through the pedun- cle. Dinophysis caudata grew at a growth rate of 1.03 divisions day � 1 when supplied with M. rubra as prey, reaching a maximum concentration of ca. 5,000 cell well � 1 (810 mL) during a 9 day growth experiment. In contrast, a culture of D. caudata was not able to be established in the absence of the ciliate or when provided with T. amphioxeia only, suggest- ing that D. caudata can not directly utilize T. amphioxeia as prey.

International audience; In this study, we identified 9 polymorphic compound microsatellite markers in the toxic dinoflagellate Alexandrium catenella, which was isolated from Thau lagoon (France, Mediterranean Sea), using the compound microsatellite marker technique. These new microsatellites were characterized by screening DNA templates from 43 A. catenella clonal strains, which were collected from a seawater sample from Inokushi Bay (Oita Prefecture, Japan). These loci provide one class of highly variable genetic marker: the number of alleles ranged from 3 to 8, and the estimate of gene diversity varied between 0.285 and 0.762. We also analyzed the same 43 DNA samples using microsatellite markers previously identified for A. catenella, comparing the PCR amplification success, the number of alleles and gene diversity. These three parameters were not significantly different, showing that the compound microsatellite markers have the same potential to reveal A. catenella genetic structure. This simple and efficient method reduces the costs for developing SSR markers and for analyzing the genetic structure of populations, therefore, suggesting the effectiveness of applying this method to other species.

We isolated 24 polymorphic microsatellite markers from the toxic dinoflagellate A. tamiyavanichii. These loci provide a class of highly variable genetic markers, as the number of alleles ranged from 2 to 6, and the estimate of gene diversity was from 0.269 to 0.739 across the 24 microsatellites. We consider that these loci have a potentially to reveal the genetic structure and gene flow among A. tamiyavanichii populations.

We isolated 15 polymorphic microsatellites from one of the most noxious red tide-causing dinoflagellate species, Heterocapsa circularisquama . These loci provide one class of highly variable genetic markers, as the number of alleles ranged from two to six, and the estimate of gene diversity was from 0.205 to 0.684 across the 15 microsatellites. These loci have the potential to reveal genetic structure and gene flow among H. circularisquama populations.

We isolated 15 polymorphic microsatellites from Cochlodinium polykrikoides. These loci provide a class of highly variable genetic markers, as the number of alleles ranged from two to 15, and the estimate of gene diversity was from 0.083 to 0.880 across the 15 microsatellites. We consider that these loci have a potential to reveal the genetic structure and gene flow among C. polykrikoides populations.

Kleptoplastidy is the retention of plastids obtained from ingested algal prey, which may remain temporarily functional and be used for photosynthesis by the predator. We showed that the marine dinoflagellate Dinophysis mitra has great kleptoplastid diversity. We obtained 308 plastid rbc L sequences by gene cloning from 14 D. mitra cells and 102 operational taxonomic units (OTUs). Most sequences were new in the genetic database and positioned within Haptophyceae (227 sequences [73.7%], 80 OTUs [78.4%]), particularly within the genus Chrysochromulina . Others were closely related to Prasinophyceae (16 sequences [5.2%], 5 OTUs [4.9%]), Dictyochophyceae (14 sequences [4.5%], 5 OTUs [4.9%]), Pelagophyceae (14 sequences [4.5%], 1 OTU [1.0%]), Bolidophyceae (3 sequences [1.0%], 1 OTU [1.0%]), and Bacillariophyceae (1 sequence [0.3%], 1 OTU [1.0%]); however, 33 sequences (10.8%) as 9 OTUs (8.8%) were not closely clustered with any particular group. Only six sequences were identical to those of Chrysochromulina simplex , Chrysochromulina hirta , Chrysochromulina sp. TKB8936, Micromonas pusilla NEPCC29, Micromonas pusilla CCMP491, and an unidentified diatom. Thus, we detected >100 different plastid sequences from 14 D. mitra cells, strongly suggesting kleptoplastidy and the need for mixotrophic prey such as Laboea , Tontonia , and Strombidium -like ciliates, which retain numerous symbiotic plastids from different origins, for propagation and plastid sequestration.

Monitorings were conducted on DSP toxins in mid-gut gland of scallop (mouse assay), cell numbers of toxic dinoflagellate species of Dinophysis, and diarrhetic shellfish poisoning (DSP) toxins in small-sized (0.7-5 microm) plankton fraction of seawater collected from surface (0 m) and 20 m depth at a station in Mutsu Bay, Aomori Prefecture, Japan, in 2000. A specific enzyme-linked immunosorbent assay (ELISA) was employed for the analysis of DSP toxins in small-sized plankton fraction using a mouse monoclonal anti-okadaic acid antibody which recognizes okadaic acid, dinophysistoxin-1, and dinophysistoxin-3. DSP toxins were detected twice in the mid-gut gland of scallops at 1.1-2.3 MU (mouse units) g(-1) on 26 June and at 0.6-1.2 MU g(-1) on 3 July, respectively. Relatively high cell densities of D. fortii were observed on 26 June and 11 September, and may only contribute to the bivalve toxicity during late June to early July. D. acuminata did not appear to be responsible for the toxicity of scallops in Mutsu Bay in 2000. ELISA monitoring of small-sized plankton fraction in seawater could detect DSP toxins two weeks before the detection of the toxin in scallops, and could do so two weeks after the loss of the bivalve toxicity by mouse assay. On 17 July, toxic D. fortii was detected at only small number