Toxin variability in cultured and natural populations of Alexandrium tamarense from southern South America - Evidences of diversity and environmental regulation.

Cell content and composition of paralytic shellfish toxins of 10 cultured strains and 6 natural populations of Alexandrium tamarense from the Argentine sea, were analyzed. These data were compiled with previously published data into a comprehensive view of the toxin composition of the complex A. tamarense/Alexandrium catenella from southern South America. The N-sulfocarbamoyl derivatives C1,2 were predominant in almost all the cultured strains. The second major derivatives were GTX1,4, although the GTX1,4/C1,2 ratio varied largely. Some strains contain relatively high amounts of GTX2,3 (up to 29%) and/or neoSTX (up to 24%). In all strains STX was a minor component (0-4.4%) whereas GTX5 was present only in Alexandrium catenella isolates. Similarity analysis based upon toxin profiles showed that cultured strains from Argentine, Brazil, Chile and Uruguay clustered together. However, whereas some strains from the same geographic area exhibited different toxin profiles, and consistently fell out in separate subgroups, strains from Chile are grouped in a unique subgroup. In contrast to cultured strains, C1,2 were minor components among field populations. The highly toxic GTX1,4 were predominant in all spring field populations (69.1-93.6%). Moreover, their toxin cell content (163.9-261.4 fmol cell(-1)) and toxicity (68.2-93.0 pg STX equiv. cell(-1)) were several times higher that showed by the cultured strains. Field populations are more closely related to one another than to the cultured strains. However a less toxic and morphologically distinctive autumn population, contained GTX2,3 as the quasi unique (88.5%) toxin derivative clustered separately. Variability in toxin content and composition of A. tamarense field populations were well correlated with in situ temperature and nitrate concentration. Whereas toxin cell content and GTX1,4 (mol %) increased following saturation functions, GTX2,3 (mol %) decrease exponentially with the increase of the in situ nitrate concentration.