Molecular discrimination of toxic and non-toxic Alexandrium species (Dinophyta) in natural phytoplankton assemblages from the Scottish coast of the North Sea.

Molecular methods provide promising tools for routine detection and quantification of toxic microalgae in plankton samples. To this end, novel TaqMan minor groove binding probes and primers targeting the small (SSU) or large (LSU) ribosomal subunit (rRNA) were developed for two species of the marine dinoflagellate genusAlexandrium(A. minutum,A. tamutum) and for three groups/ribotypes of theA. tamarensespecies complex: Group I/North American (NA), Group II/Mediterranean (ME) and Group III/Western European (WE). Primers and probes for real-time quantitative PCR (qPCR) were species-specific and highly efficient when tested in qPCR assays for cross-validation with pure DNA from culturedAlexandriumstrains. Suitability of the qPCR assays as molecular tools for the detection and estimation of relative cell abundances ofAlexandriumspecies and groups was evaluated from samples of natural plankton assemblages along the Scottish east coast. The results were compared with inverted microscope cell counts (Utermöhl technique) ofAlexandriumspp. and associated paralytic shellfish poisoning (PSP) toxin concentrations. The qPCR assays indicated thatA. tamarense(Group I) andA. tamutumwere the most abundantAlexandriumtaxa and both were highly positively correlated with PSP toxin content of plankton samples. Cells ofA. tamarense(Group III) were present at nearly all stations but in low abundance.Alexandrium minutumandA. tamarense(Group II) cells were not detected in any of the samples, thereby arguing for their absence from the specific North Sea region, at least at the time of the survey. The sympatric occurrence ofA. tamarenseGroup I and Group III gives further support to the hypothesis that the groups/ribotypes of theA. tamarensespecies complex are cryptic species rather than variants belonging to the same species. [ABSTRACT FROM PUBLISHER]

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