Takehiko Ogata

Effect of water temperature and light intensity on growth rate and toxicity change in Protogonyaulax tamarensis

The effect of water temperature and light intensity on the growth rate and the toxicity of Protogonyaulax tamarensis was examined using a monoclonal culture isolated from Ofunato Bay, Japan in March, 1984. The growth rate decreased with the decrease of either light intensity or temperature. The amount of toxin produced increased concomitantly with the decrease of the growth rate. However, the increase of the toxicity under low growth rate was less remarkable when the growth rate was lowered by the decrease of light intensity. This indicates that photosynthesis plays an important role in the production of toxin in P. tamarensis.

Production of paralytic shellfish toxins by a bacterium Moraxella Sp. isolated from Protogonyaulax tamarensis

A bacterium Moraxella sp. isolated from Protogonyaulax tamarensis was cultured in various conditions. Changes of toxicity and toxin components of the cells during culture were analyzed by bioassay and HPLC-fluorometric analysis. Toxin productivity of Moraxella sp. increased when it was cultured in nutrition-deficient environments. The main toxins produced by Moraxella sp. in these conditions were gonyautoxins (GTXs), mainly GTX 1 and 4 which are major toxins of P. tamarensis.

Excitation energy transfer in carotenoid-chlorophyll protein complexes probed by femtosecond fluorescence decays

Abstract An energy transfer pathway in a carotenoid-chlorophyll a protein complex of dinoflagellates was studied by the femtosecond up-conversion method. The energy levels of the S 2 state of peridinin and their lifetime were essentially identical in methanol and in the complex. The S 1 lifetime of peridinin in solvents was more than 30-fold longer than in the complex. These results account for an observed transfer efficiency (higher than 85%) and indicate that an energy transfer occurs between the S 1 states of peridinin and chlorophyll a after a rapid internal conversion. This pathway is unique in photosynthetic organisms.

Octocoral chemical signaling selects and controls dinoflagellate symbionts.

Symbioses between zooxanthellae (Symbiodinium spp.) and marine invertebrates, including corals, are common in shallow marine environments. The zooxanthellae contribute to host nutrition by translocating photosynthetic products and enabling them to effloresce in oligotrophic conditions. Coral mainly acquire Symbiodinium spp. by capturing freeswimming cells from the environment (1). Cultured Symbiodinium cells show a diel growth cycle with alternation between motile and non-motile cell stages once a day (2, 3), and the cell divides only during the latter stage (2). When associated with a host, however, cells are arrested in a non-motile stage while healthy cell division is maintained (4). We deduced that host-directed and chemical-based mechanisms are responsible for this phenomenon since SLL-2, a lectin that binds to carbohydrate chains with a D-galactosyl moiety, produced by the octocoral Sinularia lochmodes, is localized on the cell surface of the Symbiodinium harbored in the host (5). Here we describe SLL-2 as the key chemical factor for arresting Symbiodinium in the cell-dividing, non-motile stage, while some nonsymbiotic microalgae were even destroyed by SLL-2. Symbiotic associations between photosynthetic dinoflagellates (Symbiodinium spp.) and invertebrate hosts such as corals are crucial for the survival of the host animals since Symbiodinium supplies organic compounds to them and enables them to prosper in the oligotrophic environment

EFFECTS OF LIGHT AND TEMPERATURE ON GROWTH, NITRATE UPTAKE, AND TOXIN PRODUCTION OF TWO TROPICAL DINOFLAGELLATES: ALEXANDRIUM TAMIYAVANICHII AND ALEXANDRIUM MINUTUM (DINOPHYCEAE)†

The two tropical estuarine dinoflagellates, Alexandrium tamiyavanichii Balech and A. minutum Halim, were used to determine the ecophysiological adaptations in relation to their temperate counterparts. These species are the two main causative organisms responsible for the incidence of paralytic shellfish poisoning (PSP) in Southeast Asia. The effects of light (10, 40, 60, and 100 μmol photons·m−2·s−1) and temperature (15, 20, and 25°C) on the growth, nitrate assimilation, and PST production of these species were investigated in clonal batch cultures over the growth cycle. The growth rates of A. tamiyavanichii and A. minutum increased with increasing temperature and irradiance. The growth of A. tamiyavanichii was depressed at lower temperature (20°C) and irradiance (40 μmol photons·m−2·s−1). Both species showed no net growth at 10 μmol photons·m−2·s−1 and a temperature of 15°C, although cells remained alive. Cellular toxin quotas (Qt) of A. tamiyavanichii and A. minutum varied in the range of 60–180 and 10–42 fmol PST·cell−1, respectively. Toxin production rate, Rtox, increased with elevated light at both 20 and 25°C, with a pronounced effect observed at exponential phase in both species (A. tamiyavanichii, r2=0.95; A. minutum, r2=0.96). Toxin production rate also increased significantly with elevated temperature (P<0.05) for both species examined. We suggest that the ecotypic variations in growth adaptations and toxin production of these Malaysian strains may reveal a unique physiological adaptation of tropical Alexandrium species.

Toxin production in the dinoflagellate Protogonyaulax tamarensis

Many clones of Protogonyaulax tamarensis were collected from Ofunato Bay in the same season and cultured under the same conditions. The toxicity of the cultured cells of these clones was remarkably different from each other (maximum of 100-fold). Significant differences (maximum of 20-fold) in toxicity of cultured cells were also observed among subclones isolated from a single clonal culture. It is unlikely that this variation in toxicity among subclones is due to mutation during culture. From these observations we suggest that toxin production in P. tamarensis is not a hereditary characteristic.

External secretion of tetrodotoxin from puffer fishes stimulated by electric shock

Four toxic species of puffers (Takifugu pardalis, T. poecilonotus, T. vermicularis and T. niphobles) secreted large amounts of tetrodotoxin into the surrounding water immediately after being stimulated by electric shock. The total amount of toxin secreted ranged from 2 000 to 50 000 MU depending upon the specimen. The amount of toxin secreted seemed to be related to the toxicity of individuals. Non-toxic specimens of T. rubripes did not secrete any toxin. The stimulation always caused inflation of puffers, and this is generally accepted as a repelling behavior of these species. The secreted tetrodotoxin may act as a repellent to predators.

Confirmation of domoic acid production of Pseudo-nitzschia multiseries isolated from Ofunato Bay, Japan.

Production of domoic acid (DA), the responsible toxin for amnesic shellfish poisoning, was examined for 44 strains of Pseudo-nitzschia spp. isolated from Ofunato Bay, Japan. Only one strain which was identified as Pseudo-nitzschia multiseries produced DA in a level comparable to Canadian strains. No significant DA was detected in the rest of the strains, indicating that toxic P. multiseries does not bloom in a high density in the bay.

Occurrence of saxitoxin and other toxins in the liver of the pufferfish Takifugu pardalis

Highly toxic livers of the pufferfish Takifugu pardalis were extracted with acidic ethanol. The toxins extracted were partially purified by chromatography on Bio-Gel P-2 and then Bio-Rex 70, resulting in separation into three fractions I, II and III. ratios of total mouse units per fraction were approximately 0.1:100:0.01, respectively, with tetrodotoxin (TTX) as standard. By TLC, electrophoresis and a TTX analyzer, Fr. II was identified as TTX and, unexpectedly, Fr. III as saxitoxin, while Fr. I remains unidentified.

Frequent occurrence of paralytic shellfish poisoning toxins as dominant toxins in marine puffer from tropical water

Considerably high toxicity was detected in marine puffers collected from Masinloc Bay, Philippines. The toxicity was detected in the liver, intestine, muscle and skin. Noteworthy, the specimens, the muscle of which showed high toxicity, appeared in high frequency, indicating that puffers from this area is not safe for human consumption. These puffer specimens contained paralytic shellfish poisoning (PSP) toxins, often as major toxin components, the profile of which was similar to that of freshwater puffers reported from tropical areas. These results indicate that PSP toxins are common in tropical puffers both from marine and freshwater.