ABSTRACT: Interactions between bacteria and harmful algae are potentially important regulating factors for population dynamics of both organisms and for toxin production. These interactions are still poorly understood. To monitor the physical associations between potentially toxic bacteria and dinoflagellates in controlled conditions, we inoculated an axenic non-toxic strain of Alexandrium tamarense (Dinophyceae) together with reputed paralytic shellfish toxin (PST)-producing bacteria belonging to the genus Alteromonas (g subdivision of the division Proteobacteria) and to the clade Roseobacter (a subdivision of the division Proteobacteria). The attachment behavior of both bacterial strains was monitored using TSA-FISH (tyramide signal amplification and fluorescent in situ hybridization) and confocal microscopy. Our results suggest that ageing dinoflagellate cultures stimulate both free bacterial growth and attachment. However, toxin production by originally non-toxic dinoflagellate cells was not induced by the physical interaction of either of the bacterial strains with the dinoflagellate cells. This does not support the hypothesis that toxic bacteria could simply control toxin production by attachment to particle surfaces such as eukaryotic organisms.

KEY WORDS: Attached bacteria · Dinoflagellate · Alexandrium · Bacteria-phytoplankton interactions · In situ hybridization · Tyramide signal amplification · Confocal micoscopy

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Published in AME Vol. 28, No. 3 (2002) on July 24
Print ISSN: 0948-3055; Online ISSN: 1616-1564. Copyright © Inter-Research, Oldendorf/Luhe, 2002