Genetic diversity and molecular detection of three toxic dinoflagellate genera (Alexandrium, Dinophysis, and Karenia) from French coasts.

The objectives of this study were 1) to study the genetic diversity of the Alexandrium, Dinophysis and Karenia genera along the French coasts in order to design probes targeting specific DNA regions, and 2) to apply PCR-based detection to detect these three toxic dinoflagellate genera in natural samples. Genetic diversity of these toxic taxa was first studied from either cultures or cells isolated from Lugol-fixed field samples. By this way, partial sequences of the large ribosomal subunit (LSU rDNA) including the variable domains D1 and D2 of A. minutum, Alexandrium species inside the tamarensis complex, the D. acuminata complex and K. mikimotoi were obtained. Next, specific primers were designed for a selection of toxic algae and used during semi-nested PCR detection. This method was tested over a 3-month period on water samples from the Bay of Concarneau (Brittany, France) and on sediment from the Antifer harbor (The English Channel, France). Specificity and sensitivity of this molecular detection were evaluated using the occurrence of target taxa reported by the IFREMER (Institut Français de Recherche pour l'Exploitation de la Mer) monitoring network based on conventional microscopic examination. This work presents the first results obtained on the biogeographical distribution of genotypes of these three toxic genera along the French coasts.

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.