C. Maclean, A. D. Cembella, M. A. Quilliam
Effects of Light, Salinity and Inorganic Nitrogen on Cell Growth and Spirolide Production in the Marine Dinoflagellate Alexandrium ostenfeldii (Paulsen) Balech et Tangen
Small-volume batch cultures of the toxic marine dinoflagellate Alexandrium ostenfeldii (Paulsen) Balech et Tangen were exposed to gradients of salinity, light, and inorganic nitrogen to determine their effects on growth and toxin production. Cell growth was determined by in vivo fluorometry and microscopic cell counts, and spirolide production through the culture cycle was measured by liquid chromatography-mass spectrometry. Growth of A. ostenfeldii was a function of environmental conditions, and was strongly limited under suboptimal regimes of light (? 150 ?mol m?2 s?1), salinity (? 15 psu), and low nutrients (? 20 ?M initial nitrate). Cell concentration and in vivo fluorescence were highly correlated (r2 = 0.83 to 0.97, n = 6) but the relationship varied slightly depending on experimental conditions. Nevertheless, except under nitrogen limitation, fluorometry was an accurate method for tracking cell growth. The growth characteristics indicated that this estuarine isolate of A. ostenfeldii from Atlantic Canada was moderately “shade-adapted”, had a broad salinity tolerance, and could effectively utilize much higher levels of inorganic nitrogen than commonly occur in the natural environment. Analysis of toxin production and composition throughout the culture cycle showed that total concentration of spirolides in the cellular fraction of the culture (?mol l?1) increased with cell concentration, but cell spirolide quota (Qs) and toxin composition (% molar) did not vary substantially in response to variations in environmental regime. Spirolides accumulated in the growth medium, but the concentration remained low (< 15% of total) in comparison to that in the cellular fraction. This study supports the conclusion that cell growth is directly responsive to changes in environmental variables, but spirolide production is constitutive and susceptible to acclimation in culture.
Botanica Marina, Walter de Gruyter
Print ISSN: 0006-8055
Volume: 46, 09/2003
Pages: 466 - 476
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