Influence of environmental and nutritional factors on growth, toxicity, and toxin profile of dinoflagellate Alexandrium minutum.

The toxic dinoflagellate Alexandrium minutum T1 was isolated from southern Taiwan in February 1996, grown under various environmental and nutritional conditions, and then examined for growth, toxicity, and toxin profile. It was found that the optimal environmental conditions for cell growth and toxin production of A. minutum T1 was as follows: temperature 25 degrees C, pH 7.5, light strength 120 microEm(-2) s(-1), and salinity 15 ppt. The optimal level of nutrients supplemented in the 50% natural seawater medium was as follows: phosphate 0.002%, nitrate 0.01%, cupric ion 5.0 ppb, ferric ion 270 ppb and humic acid free. Both cell toxicity and total toxicity reached the maximum level at the post-stationary growth phase and decreased quickly. The toxic components of A. minutum T1 were assayed by high performance liquid chromatography, and found to be gonyautoxin (GTX) 1-4 only. Among these four toxin components, toxins GTX 1 and 4 were the predominant components throughout the growth curve when the cells were grown in the optimal environmental and nutritional conditions. But toxins GTX 2 and 3 increased when the cells were cultured in high salinity medium.