Description: Coupling Physiological Responses of the Toxic Haptophyte Prymnesium parvum to Patterns in Gene ExpressionMichael F. Freitag1, Uwe John1 & AD Cembella11Alfred Wegener Institute for Polar and Marine research, 27576 Bremerhaven, Germany 2Sára Beszteri, Alfred Wegener Institute, Bremerhaven GermanyA normalized cDNA library2 from the toxic haptophyte Prymnesium parvum was used to design an oligonucleotide-based microarray platform. Allelopathic interactions were investigated between P. parvum strain RL10 and the heterotrophic dinoflagellate Oxyhrris marina. Cultures of Prymnesium were incubated together with both whole cells and cell-free filtrate from Oxyhrris cultures. During incubation with Prymnesium, the presence of Oxyhrris cells, compared to cell-free culture medium, showed no differential effect on the gene expression profile of the haptophyte. A bioassay measuring the toxicity of Prymnesium against the sensitive cryptophyte Rhodomonas baltica was additionally performed. In this case, Rhodomonas viabilities following incubation with Prymnesium and Prymnesium previously incubated with O. marina medium were virtually identical. This suggests no correlation between the presence of O. marina medium, and induced toxicity in P. parvum. Similar experiments, involving the dinoflagellate Heterocapsa rotunda and an unclassified toxic crooccal cyanobacteria strain: NIVA CYA 331, are currently underway. All tentative unique genes (TUGs) identified from the microarray hybridization will be further classified through the use of a Prymnesium fosmid library prepared from axenic cultures.