Toxin content differs between life stages of Alexandrium fundyense (Dinophyceae)

Different life stages of two mating-compatible clones of the paralytic shellfish toxin (PST)-producing dinoflagellate Alexandrium fundyense Balech were separated using a combination of techniques; culturing and sampling methods were used to separate vegetative cells and gametes, and sorting flow cytometry was used to separate zygotes. PST profiles were significantly different between life stages; the two gonyautoxins GTX1 and 2 were present in vegetative and senescent cells, but disappeared from gametes and zygotes. Toxin-profile changes were shown to occur very quickly in both strains when pellicle cyst formation was induced by shaking (four minutes) followed by rinsing on a screen. These pellicle cysts produced from exponentially-growing, vegetative cells lost GTX1 and 2 completely. Rapid toxin epimerization of GTX1 to GTX4 and GTX2 to GTX3 is one possible explanation, although the biological advantage of this remains unclear. Another possible explanation is that during the mating phase of a bloom or when cells are disturbed, GTX1 and GTX2 are released into the surrounding water. It may be advantageous for a dinoflagellate bloom to be surrounded by free toxins in the water.

► Two strains of A. fundyense lost GTX1 and 2 during gamete formation.
► The lost PST forms were still not present in the zygotes formed by mating gametes.
► The same PST forms were quickly lost during pellicle-cyst formation.
► Loss of toxins to the environment would lead to free toxins surrounding the bloom.
► Techniques for separation of different life stages of dinoflagellates are described.