Department of Aquaculture, Faculty of Agriculture, Kochi University, Nankoku, Kochi 783-8502, Japan
The effects of phosphorus deficiency on the growth and PSP toxin production by an axenic clone culture of Alexandrium catenella TNY7 were examined under semi-continuous culture conditions.
The specific growth rate (μ) diminished with decreasing cell quota for phosphorus (QP). The relationship between μ and QP was described by the Droop equation. The calculated maximum specific growth rate and minimum cell quota for phosphorus were 0.79day−1 and 0.28 pmol/cell, respectively. Toxin content per cell increased with decreasing specific growth rate. When phosphorus limitation in the cells was the most severe, the highest toxin content per cell (92.3 fmol/cell) was obtained. The highest toxin content per cell was approximately 4 to 6 times higher than in nutrient sufficient conditions and 22 times higher than in nitrogen deficient conditions. Toxin composition and ratio remained constant independent of specific growth rate and phosphorus limitation in the cells.
Phosphorus limitation is one of the most important environmental factors which increase the total toxin per cell of A. catenella. Phosphorus limited cells of A. catenella may have some effect on increase in toxin content of shellfish in natural waters.