Investigations into the role of bacteria-dinoflagellate interactions in paralytic shellfish poisoning

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Fluorescently-labelled 16S and 23S rRNA oligodeoxynucleotide probes, group or clade specific, respectively, were used to identify bacteria associated with Alexandrium spp. by confocal laser scanning microscopy (CLSM). Bacteria were found to be associated with Alexandrium tamarense, A. lusitanicum and A. andersonii, intra- and/ or extracellulary, respectively. The presence of metabolically active intracellular bacteria in dinoflagellates of the genus Alexandrium was documented with the use of 5-cyano-2,3-ditolyl tetrazolium chloride (CTC). This compound is reduced by living, respiring bacteria into a water-insoluble fluorescent formazan (CTF), which fluorescences bright red. Actively respiring bacteria were detected intracellularly in log and stationary phase-fixed A. tamarense and A. lusitanicum by epifluorescence microscopy (FM) and CLSM. These results support the given theory that specific bacteria are an integral part of the physical environment of Alexandrium spp. Key words: Alexandrium, bacteria, confocal laser scanning microscopy, cyanoditolyltetrazolium chloride (CTC), dinoflagellates, epifluorescence microscopy, 16S rRNA probes, 23S rRNA probes, Paralytic Shellfish Poisoning 27