Domoic Acid production by Pseudo-nitzschia seriata (Bacillariophyceae) in Scottish waters

Abstract

In 1999, a 49,000km2 area in western Scottish waters was closed to shellfish harvesting due to the amnesic shellfish poisoning (ASP) toxin domoicacid (DA). The only previously confirmed DA producer identified had been Pseudo-nitzschia australis Frenguelli. The toxin has appeared every year since and has led to more harvesting closures. We isolated and cultured two strains of Pseudo-nitzschia seriata f. seriata (P. T. Cleve) H. Peragallo from western Scottish waters in 2001 and 2002. They were identified using TEM analysis of their morphological fine structure and sequencing of the internal transcribed spacer (ITS)1, 5.8S, ITS2, and partial large subunit (LSU) rDNA. The morphology of the Scottish P. seriata f. seriata strains differed slightly, for example, in the number of poroid rows, from descriptions in identification keys. Comparison of P. seriata sequences with those of two co-occurring Pseudo-nitzschia australis isolates showed an overall divergence of only 0.012. Sequence divergence between both species was highest in the ITS1 region (0.036). Combined morphological and genetic approache sare needed to identify closely related Pseudo-nitzschia species. The P. seriata strains grew successfully at 15 degrees C, suggesting that although see nas a psychrophilic species, it may also occur at higher water temperatures. All isolates produced DA in stationary phase (measured on day 25): 0.16–0.23 pg DA.per cell in P. seriata and 0.15–1.68 pg DA per cell in P. australis. Our study is the first to identify P. seriata f. seriata as a DA producer in Scottish waters and indicates that at least it and P. australis can be responsible for ASP toxicity in that region.