Effects of salinity, light and inorganic nitrogen on growth and toxigenicity of the marine dinoflagellate Alexandrium tamarense from northeastern Canada

Abstract

Growth and toxin production of a highly toxic clone of the marine dinoflagellate Alexandrium tamarense, isolated from the lower St Lawrence Estuary (quebec) in eastern Canada, were studied in unialgal batch cultures under different conditions. Controlled experiments were conducted on the production of paralytic shellfish poisoning (psp) toxins under conditions of varying light (40, 60, 150, 230 and 470 μmol m-2 s-1), salinity (10, 15, 20, 25 and 30‰) and nitrate concentrations (0, 88, 264, 528 and 880 μmol l-1). The effects of variable environmental factors on both toxin composition (% molar) and cell toxicity [pg STXeq (saxitoxin equivalents) cell-1] were determined through the culture cycle. The toxin profile (% molar; mean ± Sd), determined by high-performance liquid chromatography with fluorescence detection (HPLC-FD), remained stable and was consistently dominated by the low-potency N-sulfocarbamoyl toxins C1/C2 (64.0 ± 3%). There were also substantial relative amounts of the high-toxicity carbamate derivatives gonyautoxin 1-4 (GTX1-4) (1.7 ± 0.5%), neosaxitoxin (NEO) (16.2 ± 2%) and saxitoxin (STX) (17.8 ± 2%). The cellular toxicity (mean ± SD: 58.8 ± 7 pg STXeq cell-1) was essentially independent of light, salinity and nitrate concentration throughout the exponential growth phase, but varied over the growth stages in culture. A positive correlation was observed between cellular toxicity and salinity-dependent growth rate, indicating that cell toxin quota may be affected by extrinsic factors, but it is not always a direct functional response to specific environmental stress.