Strain dependent production of ciguatoxin precursors (Gambiertoxins) by Gambierdiscus toxicus (Dinophyceae) in culture

Thirteen strains of Gambierdiscus toxicus isolated from Queensland (Australia), Hawaii, French Polynesia and the Virgin Islands were mass cultured and extracted for ciguatoxin. A biodetrital sample containing wild G. toxicus collected from the Republic of Kiribati was also extracted for ciguatoxin. Ciguatoxin, as characterized from moray eels, was not detected in any of the strains examined. Two Queensland strains and the wild G. toxicus produced putative ciguatoxin precursors named gambiertoxins. These gambiertoxins were less polar than ciguatoxin but produced bioassay signs in mice and in-vitro responses in isolated guinea pig atria and vas deferens which were similar (but not identical) to those produced by ciguatoxin. The gambiertoxins from cultured cells were also shown to competitively inhibit the binding of [3H]brevetoxin-3 to rat brain membranes in a dose-dependent manner. The gambiertoxins were more potent than ciguatoxin (on a per mouse unit basis) at stimulating neural elements of guinea pig atria. The two culture strains produced similar amounts of gambiertoxins, even when grown in nutrient media made from different seawater containing different concentrations of nutrients. Changes in nutrient media did not induce the other strains of G. toxicus to produce gambiertoxins. The production of these ciguatoxin precursors appears to be limited to only certain genetic strains of G. toxicus, with the majority of strains not producing these toxins. We propose that ciguatera occurs when blooms of G. toxicus strains genetically capable of producing these ciguatoxin precursors enter the marine food chain. These toxins could then become oxidatively metabolized in fishes to the more polar ciguatoxin. Wild cells produced approximately 100-fold greater quantities of gambiertoxins per cell than did the two culture strains indicating that there is considerable potential for increased production of these ciguatoxin precursors from G. toxicus in culture.