CHANGES IN TOXIN CONTENT, BIOMASS AND PIGMENTS OF THE DINOFLAGELLATE ALEXANDRIUM-MINUTUM DURING NITROGEN REFEEDING AND GROWTH INTO NITROGENOR PHOSPHORUS STRESS

Two strains of the paralytic shellfish toxin (PST) producing dinoflage llate Alexandrium minutum Halim (highly toxic AL1V and weakly toxic AL 2V) were grown in batch culture with either nitrate or phosphate as th e Limiting nutrient. In comparison with cells of the strain AL1V, cell s of AL2V grew at a similar C-specific rate, had a higher CIN ratio, a nd lower ratios of chl a/chl c(2) and chl a/peridinin. Neither chlorop hylls nor carotenoids could be used to estimate C-biomass, N-biomass o r toxin content for this organism. The toxin profile for both strains was dominated (up to 95%) by the gonyautoxin GTX4, with smaller propor tions of GTX1, GTX2 and GTX3. The rate of toxin synthesis for both str ains was greatest 1 to 2 d after the N-refeeding of N-deprived cells, with the net rate of toxin synthesis exceeding that of C-biomass and c ell division by a factor of up to 4. Toxin synthesis was not enhanced by short-term P-stress. N-stress alone led to a decrease in toxin cell (-1), but P-stress followed by N-stress did not result in such a decli ne, implicating phosphorus in the regulation of toxin metabolism. Alth ough arginine is a major precursor for PST synthesis, taurine, glycine , glutamine, and cell N showed similar relations to that observed for arginine with respect to toxin content. Furthermore, the mole ratio of arginine/toxin could vary by a factor of up to 5 between AL1V and AL2 V at peak values of toxin cell(-1), and by more than 5 within a strain when growing under different conditions. These observations suggest t hat the relationship between free arginine content and toxin content i s complex. No explanation for the higher toxin content of AL1V is appa rent, except that AL1V has a higher N-content per cell. and this may b e conducive to a higher rate of synthesis of the N-rich toxins.