Effects of selenium, iron and cobalt addition to growth and yessotoxin production of the toxic marine dinoflagellate Protoceratium reticulatum in culture

The marine dinoflagellate Protoceratium reticulatum has been recently identified as a source for the disulfated polyether toxin, yessotoxin (YTX), and may pose a risk to human health, aquaculture development and coastal environments. The requirements of P. reticulatum for selenium, iron and cobalt were assessed in culture. P. reticulatum was grown in nutrient enriched seawater (1/10 GP medium) without selenium or with 0.003 and 0.0003 μM selenium added; without iron or with 0.076 and 0.0076 μM iron added; and without cobalt or with 0.008 μM cobalt added. Test flasks were monitored for growth rate, cell yield and YTX production. P. reticulatum was found to exhibit a strong requirement for both selenium and iron. Growth rate and cell yield in treatments without added selenium were significantly (P<0.05) reduced to 60.2% (μ=0.15 day⁻¹) and 20.2% (4942 cell ml⁻¹), respectively, of those with selenium added (μ=0.23 day⁻¹ and 24, 387 cell ml⁻¹). YTX production was significantly increased by addition of selenium in two of three transfers tested. Cells of P. reticulatum subjected to medium without selenium added showed morphological changes observable at the light microscope level which included enlarged cell size. The diameter of cells in medium without selenium added were significantly (P<0.05) enlarged to 36.7±0.90 μm compared to cells in the medium with selenium added, 27.5±1.25 μm. Growth rate and cell yield in treatments without added iron were also significantly reduced to 70.1% (μ=0.16 day⁻¹) and 34.2% (8003 cells ml⁻¹), respectively, of those with iron added (μ=0.23 day⁻¹ and 23,416 cells ml⁻¹). No significant effect on YTX production was measured. In contrast to selenium and iron, no limitation of growth or cell yield or differences in YTX production were observed for flasks without cobalt as compared to those with cobalt added. The possibility that harmful algal events of P. reticulatum may be influenced by selenium or iron in neritic waters is discussed.