Three species of the dinoflagellate genus Alexandrium (Halim) - two strains of toxic. A. minutum, one each of nontoxic A. tamarense and A. affini - were grown in batch culture in either a low-nitrogen or a low-phosphate medium. Maximum carbon-specific growth rates for A. tamarense were lower (at <0.25 d(-1)) than for the other strains, which all exceeded 0.38 d(-1). C-quotas (C content per cell) during exponential growth were similar for all strains (similar to 2.5 ng C cell(-1)), with cells becoming smaller during the N-limiting stationary phase, but enlarging during prolonged P-deprivation. Values of delta C-13 during the exponential phase were low (-25 to -30), with most cells during the light phase swimming at the surface when nutrient-replete and migrating to the bottom of the flasks when nutrient-deplete with delta C-13 rising to around -15. Biomass could not be estimated reliably from pigmentation, but could be estimated from biovolume (r > 0.95), although this was complicated in cultures of A. minutumm by the presence of particles comprized of thecal plates of a similar size to intact cells. Alkaline phosphatase activity was not a reliable indicator a P-status. The most toxic strain tested (A. minutum AL1V) contained the highest concentrations of free amino acids, of arginine (a precursor of paralytic shellfish toxins) and of proline, and also had the lowest C:N mass ratio (at 4.3). A. affini contained the lowest concentrations of arginine, and A. tamarense the highest exponential phase C:N (7.8). For all strains, the mole ratio of intracellular glutamine:glutamate (Gln:Glu, which was abnormally high compared to other algae) could only be used to indicate the presence or absence of N-stress rather than the degree of stress. Additions of ammonium and phosphate resulted in increases in Gln:Glu within 20 min in N-stressed cells and also enhanced toxin content in A. minutum (mainly gonyautoxin) 4 over a 24 h period.
|Number of pages||10|
|Publication status||Published - 1996|
- INTRACELLULAR AMINO-ACIDS
- Marine & Freshwater Biology