Seasonal occurrence at a Scottish PSP monitoring site of purportedly toxicbacteria originally isolated from the toxic dinoflagellate genus Alexandrium

There is increasing evidence that bacterial-algal interactions play a role in Harmful Algal Bloom (HAB) ecology. Bacteria that are associated with blo om-forming algal species, specifically toxic dinoflagellate algae, have bee n implicated in the production and biotransformation of paralytic shellfish toxins (PSTs). To clarify the role that these bacteria may play in the pro duction of PSTs, it is desirable to identify and localize the bacteria asso ciated with the dinoflagellates and enumerate them during the course of the algal blooms that the toxic dinoflagellates produce. Because 16S rRNA-targ eted probes offer the possibility of both, we previously made and tested pr obes for some putatively toxigenic bacteria isolated from cultures of the P SP-related dinoflagellates Alexandrium tamarense, A. affine and A. lusitani cum. The bacteria isolated from the dinoflagellates belong primarily to the alpha-proteobacterial group of Roseobacter and the gamma-proteobacterial. group of Alteromonas. Here, we report the successful application of these p robes to Lugol's-fixed seawater samples. We detected these bacteria in high numbers in the water column when Alexandrium spp. were both present and ab sent, and during periods when mussels contained PSTs.