Characterization of Nontoxic and Toxin-Producing Strains ofAlexandrium minutum(Dinophyceae) in Irish Coastal Waters

Abstract

A comparative analysis of the morphology, toxin composition, and ribosomal DNA (rDNA) sequences was performed on a suite of clonal cultures of the potentially toxic dinoflagellate Alexandrium minutum Halim. These were established from resting cysts or vegetative cells isolated from sediment and water samples taken from the south and west coasts of Ireland. Results revealed that strains were indistinguishable, both morphologically and through the sequencing of the D1-D2 domain of the large subunit and the ITS1-5.8S-ITS2 regions of the rDNA. High-performance liquid chromatography fluorescence detection analysis, however, showed that only strains derived from retentive inlets on the southern Irish coast synthesized paralytic shellfish poisoning (PSP) toxins (GTX2 and GTX3), whereas all strains of A. minutum isolated from the west coast were nontoxic. Toxin analysis of net hauls, taken when A. minutum vegetative cells were in the water column, revealed no PSP toxins in samples from Killary Harbor (western coast), whereas GTX2 and GTX3 were detected in samples from Cork Harbor (southern coast). These results confirm the identity of A. minutum as the most probable causative organism for historical occurrences of contamination of shellfish with PSP toxins in Cork Harbor. Finally, random amplification of polymorphic DNA was carried out to determine the degree of polymorphism among strains. The analysis showed that all toxic strains from Cork Harbor clustered together and that a separate cluster grouped all nontoxic strains from the western coast.

An evaluation of the applicability of microarrays for monitoring toxic algae in Irish coastal waters

“…They are also highly unlikely to be present in field samples from Ireland. A. minutum (AminuS01_25) and A. ostenfeldii (AostS02_25) probes showed a weak signal across all samples; however A. minutum is the most likely species present in the field samples especially in the North Channel Cork Harbour sample CH8701, which has been known for its contamination of shellfish with paralytic shellfish poisoning (PSP) toxin (Touzet et al 2007;. In general the Alexandrium microarray results correlated poorly with the cell counts, with numerous false positives and negatives.…”

“…I-3; Groben and Medlin 2005;Scholin et al 1998;Tang et al 2012;Touzet et al 2007;2010). The procedure of whole cell format is easy to operate, and intact cells can be identified by rough morphological features but advantageously nonspecific signals can be discerned from specifically labelled cells more easily (Miller and Scholin 1998).…”

“…Both Killary Harbour and Galway Bay are unpolluted and have a thrieving shellfish industry, which was estimated to be worth approximately €60 million annually to the Irish economy (Browne et al 2007). However, the potentially eutrophic North Channel of Cork Harbour is a location were PSP producing Alexandrium minutum blooms occur regularly during the summer months (Touzet et al 2007). PSP events have resulted in the closure of shellfish harvesting in Cork Harbour in most years since 1996 (Ní Rathaille et al 2008;2009 …”

“…Due to the small size of P. parvum and P. polylepis, the additional use of calcofluor/DAPI UV filter with FISH probes gives confirmation of the species present and also helps discriminate between fluorescent detritus material and other phytoplankton taxa found in the spiked field samples from the target Prymnesium sp. cells (Touzet and Raine, 2007).…”

“…These probes can be applied to whole-cell or cell-homogenate based methods of detection. The whole-cell approach maintains the target species remains intact throughout the assay procedure; an example is Fluorescent in-situ Hybridisation (FISH) analysis that is used to quantify and identify target taxa in environmental samples Simon et al , 2000Touzet et al 2007;2010). Cell-homogenate probe techniques on the other hand require the lysis of cells.…”