The growth characteristics of the raphidophyte Heterosigma akashiwo was summarized with respect to nutrients (nitrogen, phosphorus), organic matters, vitamins, trace metals especially iron, and ability of mixotrophy ingesting heterotrophic bacteria and cyanobacteria. H. akashiwo utilizes nitrate and ammonium as nitrogen and phosphate as phosphorus, and showed poor ability of utilizing organic forms. Luxury uptake was observed for phosphate and pooled phosphorus was polyphosphate. Minimum cell quota were 1.44 pmol /cell for nitrogen and 0.095 pmol /cell for phosphorus. Vitamin B12 was essentially needed for the growth of H. akashiwo, and also excessively accumulated inside cells. Iron is strictly required for the growth of H. akashiwo, and organic ligands contributed to iron utilization. Mixotrophy was reported in H. akashiwo ingesting heterotrophic bacteria and photosynthetic cyanobacteria of Synechococcus sp. Mixotrophy is considered to contribute to the bloom occurrences due to advantages for obtaining trace elements and trace organic matters that are essential and/or helpful for the growth of H. akashiwo.
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