Pseudo-nitzschia is a pennate diatom of global importance due to its production of the neurotoxin domoic acid that can cause Amnesic Shellfish Poisoning and Domoic Acid Poisoning. It has been recorded from nearly every major marine and estuarine environment and domoic acid has been found in the tissue or feces of organisms in multiple trophic levels in the oceans. Studies show that blooms of Pseudo-nitzschia spp. are increasing in frequency and duration due to changes in coastal nutrients (Anderson et al. 2002, Dortch et al. 1997, Parsons et al. 2002). It is often found in areas of upwelling or nutrient enrichment. The genus can be recognized by its characteristic "step-chain" formation. Approximately 12 Pseudo-nitzschia species are documented domoic acid producers. On the west coast of the United States, the major DA producers are P. australis, P. multiseries and P. cf. pseudodelicatissima (could be P. cuspidata; Adams et al. 2000, Stehr et al. 2002, Lundholm et al. 2003, Bates & Trainer 2006). Pseudo-nitzschia pseudodelicatissima, P. seriata and P. calliantha have caused DA contamination in shellfish in Atlantic Canada (Bates et al. 1998, Bates & Trainer 2006). In Europe, the toxigenic species are P. seriata, P. australis and P. multiseries (Bates & Trainer 2006). In New Zealand P. australis is the main source of domoic acid (Rhodes et al. 1998). The reason for domoic acid production is not fully understood. Laboratory analyses show cultures of Pseudo-nitzschia produce domoic acid under silicate or phosphate limitation, but not nitrogen or light limitation. Field studies in the Pacific Ocean and laboratory studies have found increased domoic acid production under conditions of iron limitation. More information about domoic acid production under nutrient stress can be found in Bates (1998), Maldonado et al. (2002), Wells et al. (2005), Bates et al. (2000), Pan et al. 1998), Pan et al. (1996) and Trainer et al. (2009).
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