Evelyne Erard-Le Denn

Comparison of allelopathic properties in three toxic Alexandrium species

Abstract The allelopathic property of three toxic Alexandrium species was studied using bioassays. The repressive action of the filtrate of Alexandrium cultures on growth of Chaetoceros gracile , Gymnodinium mikimotoi and Scrippsiella trochoidea was compared with the haemolytic activity of these filtrates, and published values of toxin content in Alexandrium cells. The results revealed that in the exponential phase of growth in all three species of Alexandrium cultured, allelopathic activity was positively related to both haemolytic and toxic activities, as suggested by previous workers for the same Alexandrium strains. However, in the stationary phase, the allelopathic activity was observed to be higher in relation to haemolytic and toxic activity than in the log phase.

Selective surface adhesion of the toxic microalga Alexandrium minutum induced by contact with substituted polystyrene derivatives

On the basis of observations that biospecific random copolymers (RACS) could induce phenotypic changes on contact with selected eukaryotic or prokaryotic cell lines, polystyrene derivatives of known compositions and obtained by random substitutions of sodium sulfonate and of sulfamides of aspartic acid dimethyl ester, phenylalanine and leucine, were placed in contact with swimming dinophytes of the PSP toxin producing species Alexandrium minutum and of the non-toxic species Heterocapsa triquetra. A. minutum cells exhibited higher adhesion for the random copolymer made up of polystyrene (29%), polystyrene aspartic acid dimethyl ester sulfamide (47%) and polystyrene sodium sulfonate (24%), than for samples of this series with different compositions. In contrast to this, A. minutum adhesion remained very low throughout the phenylalanine and leucine copolymer series. These results indicate that the cell-substrate adhesion phenomenon is dependent upon the final composition of the copolymer, i.e. that it is composition-specific. Taxonomic specificity was then demonstrated by presenting the PSAspOMe copolymer series with cells of the non toxic species H. triquetra (Peridinialia) related to A. minutum (Gonyaulacacea), and by observing no specific association, i.e. no signal above background levels at any composition. Specific ligand-cell adhesion is evidenced for the first time between biospecific RACS and phytoplankton, which may inspire a new generation of structures to be used in aquaculture as protective nets over shellfish clusters, or as selective filtering devices to assist in shellfish depuration from toxic microalgae.

Controlled cultivation of Alexandrium minutum and [33P] orthophosphate cell labeling towards surface adhesion tests

We describe a protocol for preparing cultures of the PSP (paralytic shellfish poisoning) dinoflagellate Alexandrium minutum, towards subsequent studies of cell adhesion onto artificial substrates. First, phenotypic uniformity of the strain used and reproducibility of the standard growth profile are obtained by optimising key parameters. Batches of A. minutum at mid-exponential proliferation phase are radiolabeled with 33P-containing medium in order to later quantify cell adhesion. A mortality corrective index is applied to the latter, using the vital fluorochrome acridine orange, i.e. dead cells show no nuclear incorporation under epifluorescence microscopy.