ABSTRACT: Alexandrium minutum T1 was cultured in four nitrogen sources of nitrate, nitrite, ammonium and
urea to study its growth kinetics and toxin production. It is found that A. minutum failed to thrive while
using nitrite as sole nitrogen source. In contrast, the maximum specific growth rates of the microalga
cultured using nitrate, ammonium and urea as nitrogen sources were 0.24 day-1, 0.22 day-1 and 0.16 day-1,
repectively. The utility efficacy of ammonium (Ks = 0.028 mM) and urea (Ks = 0.034 mM) is better than
nitrate (Ks = 0.05 mM). In comparison with nitrate, other nitrogen compounds depressed the cell toxicity.
From net toxin production rates (Rtox), the toxin production of A. minutum in the exponential growth stage
in nitrate medium was higher than that in ammonium, followed by urea and nitrite. The toxin profile was
stable and contained GTX1,2,3,4 only in all culture media. Toxins GTX1 and GTX4 were the predominant
compounds throughout the growth cycle.
