Growth and toxin production of paralytic shellfish toxin producing dinoflagellate in relation with adaptation mechanism to nutritional environment.

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1.Alexandrium tamarense and A.catenella, causative dinoflagellates of paralytic shellfish poisoning (PSP), showed selective use of amino acids for their nitrogen source, indicating that they possess some specific mechanism for incorporation of amino acids such as amino acid transporter.2.Ability to utilize organic N-source could not be confirmed for A.minutum, suggesting that nutritional character is different each other even within a same genus of Alexandrium.3.A.tamarense and A.catenella were found to use nitrate prior to organic nitrogen when these nitrogen sources coexist and to reduce their photosynthetic activity when they are using amino acid. These results suggest that these species can adapt to various nutritional environment by switching the nutrition mode between autotroph and heterotroph.4.Existence of PSP toxin binding protein was confirmed and suggested this type of toxin might explain the decrease of toxin contents in the process of amino acid utilization in A.tamarense and A.catenella.5.Examination under dark condition suggested that utilization of amino acid is one of the survival strategies for Alexandrium under unsuitable environmental condition for photosynthetic autotrophy.6.cDNAs encoding proteins involving photosynthesis and utilization of amino acid were isolated and a part of their gene expression patterns was recognized.7.Occurrence and toxin contents of Alexandrium in natural environment were suggested to be more closely related to the concentration of amino acid than that of nitrate or nitrite. In addition, excretion of scallop was found to significantly promote the growth and toxin production of A.tamarense and A.catenella.8.Growth and toxin production were examined for the Alexandrium isolated from Malaysian waters to collect basic data for the elucidation of expanding mechanisms of toxic dinoflagellates.