Detection of the ichthyotoxic dinoflagellate Gyrodinium (cf.) aureolum and morphologically related Gymnodinium species using monoclonal antibodies: a specific immunological tool

Sixteen monoclonal antibodies which recognize different cell surface antigens of the ichthyotoxic marine dinoflagellate Gyrodinium cf. aureolum were prepared and characterized for use in identification by both immunofluorescence microscopy and flow cytometry. Based on the labeling results obtained from indirect immunofluorescence assays the monoclonals could be divided into 3 groups: (I) fluorescence of the overall cell surface, (II) fluorescence of the overall cell surface together with the flagella, and (III) fluorescence of granular-like structures randomly distributed along the cell surface and at the edges of the sulcus and cingulum. Cross-reactivity of 6 selected monoclonals with other phytoplankton species revealed that labeling was restricted to G. aureolum/G. cf. aureolum and to the morphologically closely related species Gymnodinium nagasakiense and G. mikimotoi. This suggests a taxonomic proximity of these species. Fixation of samples with paraformaldehyde produced the optimal immunochemical response, resulting in the strongest fluorescence intensities. In flow cytometric analyses, labeled cells of G. cf. aureolum could be distinguished sufficiently from unlabeled controls when monoclonals of Group II and a pooled serum (combined antibodies of Groups I, II, and III) were used. This immunochemical technique will be applied in an early warning system to detect G. aureolum cells at dilute concentrations using flow cytometry or, alternatively, image analysis.