Domoic acid production and elemental composition of two Pseudo-nitzschia multiseries strains, from the NW and SW Atlantic Ocean, growing in phosphorus- or nitrogen- limited chemostat cultures.
Résumé
Here we compare cell physiology and domoic acid (DA) production for two strains of the diatom Pseudo-nitzschia multiseries originating from two opposite latitudes: Canada (CA) and Brazil (BR). The algae were grown as chemostat cultures at 0.2, 0.3 and 0.4 d-1 under nitrogen (N) and phosphorus (P) deficient conditions. The level of deficiency affected significantly the atomic C:N, C:P, C:Si and N:P ratios in both strains. In both strains P per cell was 2-4 X higher in the N- than in the P-deficient cultures. The opposite was not found for N in the P-deficient cultures, as shown by the N:P ratios and C:N ratios. The C:N and C:P ratios were significantly lower in the CA strain, and this did not change due to level of deficiency. The concentration and production of DA per cell per day, were significantly higher for both strains under P-deficiency as expected since the toxin is rich in N. However, DA was also produced by both strains during continuous cell division under N-deficiency. High or low bacterial densities associated with P. multiseries did not increase or decrease DA production. Our data imply that more attention needs to be given to the N:P ratios and concentrations in the waters where these algae occur, as both N- and P-deficiency affect DA production and cellular DA concentrations.
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