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Some species of Rhizosolenia form intense blooms, known as red tides, in Japanese coastal waters. In Tokyo Bay, Rhizosolenia setigera frequently causes red tides and sometimes causes discolouration...

Species of the benthic dinoflagellate genus Gambierdiscus are the putative producer of the toxins causing ciguatera fish poisoning (CFP) in tropical and subtropical areas. Although CFP events and distribution of G. caribaeus have been reported in Thailand, little is known about the conditions that enhance the growth of Gambierdiscus in Thailand. Hence, this study was aimed at determining the effects of temperature and salinity and their interactions on the growth of Thai G. caribaeus. The strain tested showed the highest cell yield in IMK/2 medium. Based on growth rate (μ), Thai G. caribaeus grew in the temperature range of 20°C–35°C and the salinity range of 20–40. The suboptimal condition (≥ 80% of the maximal growth rate) for the strain tested was 20.5°C–30.5°C and salinity of 25.0–37.5. The optimal condition was 25°C and salinity of 30. Furthermore, the Thai G. caribaeus revealed high toxicity to mice. Our results suggest that tolerance of up to 35°C may allow these organisms to be distribute...

Benthic dinoflagellates Ostreopsis spp. are known as producers of palytoxin and its analogs, resulting occasionally in human health problems worldwide. Although distribution of Ostreopsis spp. along the Thai coasts has been reported, little is known about their growth characteristics. To discuss the bloom dynamics of Ostreopsis spp. in Thailand, first we tested four kinds of media to optimize growth conditions and then clarified the effects of temperature, salinity and temperature–salinity interaction on the growth of strains of the O. cf. ovata Thailand subclade, O. cf. ovata South China Sea subclade, Ostreopsis sp. 6 and Ostreopsis sp. 7. We showed that the f/2 medium was a suitable medium which gave the highest cell yields for all the strains tested. The strains of the O. cf. ovata Thailand subclade, O. cf. ovata South China Sea subclade and Ostreopsis sp. 6 grew in the temperature range 20–32.5 °C, whereas the strain of Ostreopsis sp. 7 grew in 20–30 °C. The semi-optimal temperature ranges (≧80% of the maximal growth rate) for the former three strains were 22.7–27.4 °C, 27.9–30.8 °C and 23.5–26.4 °C, respectively, whereas that of the latter strain was 23–27.2 °C. The optimal temperature for the O. cf. ovata South China Sea subclade was 30 °C, whereas for the others it was 25 °C. All the Ostreopsis strains tested could grow in a salinity range of 20–40. The semi-optimal salinities for the O. cf. ovata Thailand subclade, O. cf. ovata South China Sea subclade Ostreopsis sp. 6 and Ostreopsis sp. 7 were 28.7–35, 23.8–30.8, 29.8–36 and 28–36, respectively. The optimal salinities for the O. cf. ovata Thailand subclade and O. cf. ovata South China Sea subclade were 30 and 25, respectively, whereas for Ostreopsis sp. 6 and Ostreopsis sp. 7 it was 35. In this study, our results suggested that the optimal and tolerable temperature–salinity conditions differ among the Thai Ostreopsis species/clades/subclades. Tolerances of the O. cf. ovata Thailand subclade, O. cf. ovata South China Sea subclade and Ostreopsis sp. 6 to the high temperature of 32.5 °C may allow these organisms to be distributed in the tropical areas, where the water temperature often reaches >30 °C.

Marine toxic dinoflagellates of the genus Gambierdiscus are the causative agents of ciguatera fish poisoning (CFP), a seafood poisoning that is widespread in tropical, subtropical and temperate regions of the world. In the main island of Japan, distributions of Gambierdiscus australes , Gambierdiscus scabrosus and two phylotypes of Gambierdiscus spp. type 2 and type 3, have been reported. To discuss the bloom dynamics of these Japanese species/phylotypes of Gambierdiscus , first we tested six culture media to optimize growth conditions and then clarified the effects of temperature and salinity and temperature–salinity interactions on growth. All strains of the species/phylotypes tested showed the highest cell yields when they were cultivated in IMK/2 medium. G . australes , G . scabrosus and Gambierdiscus sp. type 2 grew in the range 17.5–30 °C, whereas Gambierdiscus sp. type 3 grew in 15–25 °C. The semi-optimal temperature ranges (≥80% of the maximal growth rate) of the former three species/phylotypes were 19–28 °C, 24–31 °C and 21–28 °C, respectively, whereas that of the latter phylotype was 22–25 °C. Hence, Gambierdiscus sp. type 3 may be adapted to relatively lower water temperatures of ≤25 °C. In contrast, G . australes , G . scabrosus and Gambierdiscus sp. type 2 presumably possess adaptability to relatively high water temperatures. The optimal temperature for G . scabrosus was 30 °C, whereas the optimal temperature for the others was 25 °C. G . australes and Gambierdiscus sp. type 3 grew in a salinity range of 25–40 whereas G . scabrosus and Gambierdiscus sp. type 2 grew in salinity 20–40. Furthermore, the semi-optimal salinity range of G . australes , G . scabrosus , Gambierdiscus spp. type 2 and type 3 were salinity 27–38, 24–36, 22–36 and 29–37, respectively. Among the species/phylotypes, G . scabrosus and Gambierdiscus sp. type 2 grew even at salinity 20 where the others did not grow, thus possessing adaptability to low salinity waters. Our results clearly demonstrate that the optimal and tolerable temperature–salinity conditions differ among Japanese Gambierdiscus species/phylotypes. Considering these results, temperature–salinity interactions may play an important role in bloom dynamics and the distribution of the Gambierdiscus species/phylotypes in Japanese coastal waters.

The dinoflagellate genus Ostreopsis is known as a potential producer of palytoxin analogues. Recently a surprisingly diverse and widespread distribution of Ostreopsis along coastal waters in Japan was reported in our previous paper. In the present study, detailed toxin profiles of palytoxin analogues in several Japanese Ostreopsis strains were clarified for the first time by liquid chromatography–mass spectrometry (LC–MS). An Italian Ostreopsis strain (KAC 85) was also analyzed by LC–MS as a reference material of Ostreopsis and the presence of ovatoxin-a, -b, -c, -d, and -e was re-confirmed. The most dominant palytoxin analogue in Japanese Ostreopsis was a novel palytoxin analogue, which was identified as an isomer of ovatoxin-a. Novel isomers of ovatoxin-b, -d, and -e were also found in Japanese Ostreopsis. The isomers of ovatoxin-a, -b, -d, and -e detected in Japanese Ostreopsis were tentatively named ovatoxin-a AC, -b AC, -d AC and -e AC. LC–MS analysis suggests that ovatoxin-a AC is dideoxy-42-hydroxy-44-deoxy-palytoxin. The unidentified deoxy-positions can be assigned both between C16 and C20 and between C53 and C73. Toxin profiles of Ostreopsis collected in the middle to southern coastal area in Japan were similar irrespective of clades classified by the phylogenetic analysis reported in our previous study. The toxin contents of some strains collected in Japan were comparable to that obtained in a strain (KAC 85) collected in the Italian coast where human health problems occurred, suggesting a potential risk of Japanese Ostreopsis to human health.

Summary Benthic dinoflagellates of the genus Ostreopsis produce palytoxin (PTX)-like compounds. The worldwide distributed Ostreopsis ovata/O. cf. ovata is potentially responsible for outbreaks of human health problems around the coasts of tropical, subtropical, and temperate regions. The present study examined growth responses of an O. cf. ovata strain s0662 collected from coastal waters of Japan with 35 different combinations of temperature (15–35°C) and salinity (20–40) and discusses the bloom dynamics of the organism in Japanese coastal environments. The O. cf. ovata strain s0662 tolerated a wide range of temperature (17.5–35°C) and salinity (25–40). Results of a two-way ANOVA showed significant effects of temperature-salinity interaction on growth rates and biomass yields of the O. cf. ovata strain (F(24,70) > 127, P

Blooms of toxic dinoflagellates of the genus Ostreopsis, which is known as a producer of palytoxin (PTX) analogs, may pose a threat to human health in tropical, subtropical, and temperate regions around the world. In the present study, we established a suitable culture method for Ostreopsis spp. isolated from Japanese coastal waters and characterized their growth potential using the method to discuss their bloom dynamics. Each clonal strain of Ostreopsis cf. ovata, Ostreopsis sp. 1, Ostreopsis sp. 5, and Ostreopsis sp. 6 was incubated in 25 × 150 mm test tubes with a flat bottom containing various kinds of medium. Since Ostreopsis spp. strains grew well in IMK and/or f/2 media, we selected these media for cultivation of all the Ostreopsis spp. isolates. Growth rates of O. cf. ovata (0.834 divisions/day), Ostreopsis sp. 1 (0.619 divisions/day), and Ostreopsis sp. 6 (1.04 divisions/day) that produce PTX analogs significantly differed (p < 0.05) respectively and are clearly higher than those of other reported epiphytic dinoflagellate Gambierdiscus toxicus, Prorocentrum lima, and Coolia monotis cultures, which suggest that these species have ecological advantages to predominate through the algal succession in Japanese coastal waters, resulting in a potential risk to human health in this region.

Viruses are considered key players in phytoplankton population control in oceans. However, mechanisms that control viral gene expression in prominent microalgae such as diatoms remain largely unknown. In this study, potential promoter regions isolated from several marine diatom-infecting viruses (DIVs) were linked to the egfp reporter gene and transformed into the Pennales diatom Phaeodactylum tricornutum. We analysed their activity in cells grown under different conditions. Compared to diatom endogenous promoters, novel DIV promoter (ClP1) mediated a significantly higher degree of reporter transcription and translation. Stable expression levels were observed in transformants grown under both light and dark conditions and high levels of expression were reported in cells in the stationary phase compared to the exponential phase of growth. Conserved motifs in the sequence of DIV promoters were also found. These results allow the identification of novel regulatory regions that drive DIV gene expression and further examinations of the mechanisms that control virus-mediated bloom control in diatoms. Moreover, the identified ClP1 promoter can serve as a novel tool for metabolic engineering of diatoms. This is the first report describing a promoter of DIVs that may be of use in basic and applied diatom research.

Marine toxic dinoflagellates of the genus Gambierdiscus are the causative agents of ciguatera fish poisoning (CFP), a form of seafood poisoning that is widespread in tropical, subtropical and temperate regions worldwide. The distributions of Gambierdiscus australes, Gambierdiscus scabrosus and two phylotypes of Gambierdiscus spp. type 2 and type 3 have been reported for the waters surrounding the main island of Japan. To explore the bloom dynamics and the vertical distribution of these Japanese species and phylotypes of Gambierdiscus, the effects of light intensity on their growth were tested, using a photoirradiation-culture system. The relationship between the observed growth rates and light intensity conditions for the four species/phylotypes were formulated at R>0.92 (p

Several species of the genus Karenia (Dinophyceae) form blooms and often cause the mortality of cultured and wild fish. In Japan, blooms caused by two species - namely Karenia mikimotoi and Karenia brevis - have been reported so far. On the basis of morphological and molecular-phylogenic examinations, the present investigation found Karenia papilionacea and its novel sister phylotype for the first time in the coastal waters of the various regions of Japan. Of 34 strains isolated from the coastal waters, 27 strains displayed the typical morphological characteristics of K. papilionacea and further showed consensus DNA sequences corresponding to those of the originally described K. papilionacea. The other 7 strains displayed the same morphological characteristics of K. papilionacea, but showed divergent DNA sequences, at a genetic distance of over 0.04 (Internal Transcribed Spacer regions) from those of the original phylotype of K. papilionacea. These divergent strains were characterized as a novel sister phylotype (phylotype-I) of K. papilionacea. In the coastal waters of Japan, K. papilionacea-like (K. papilionacea and/or its phylotype-I) formed blooms at 20.3-30.4°C and salinity 30.1-33.9. No K. brevis was identified in Japanese coastal waters during this study. These findings demonstrated that K. papilionacea occurs along the coasts of western Japan and possibly shares several coastal regions with K. mikimotoi and K. papilionacea phylotype-I. In order to assess the risks of Karenia blooms to aquaculture, it is essential that the growth physiology and ichthyotoxicity of K. papilionacea and its novel phylotype should be characterized.