Domoic Acid -- A Neurotoxic Amino Acid Produced by the Marine Diatom Nitzschia pungens in Cu D. V. Subba Ras Department of Fisheries and Oceans, Bedford Institute of Oceanography (BIO), P.O. Box 7006, Dartmouth, M.S. BZY 4A2 Aedaneic Research Laboratory (ARL), National Research Council of Canada, 14 1 1 Oxford Street, Halifax, N.S. B3H 321 and R. Pocklington Department of Fisheries and Oceans, Bedford ibnseitclte of Oceanography (BIO), P.0. Box 1006, Dartmouth, N.S. B2Y 4A2 Subba Rao, D. a/., M. A. Quilliarn, and W. Pocklington. 1988. Domoic acid - a neurotoxic amino acid produced by the marine diatom Nitzschia pungens in culture. Can. 8. Fish Aquat. Sci. 45: 2076-2079. D~aring late 1987, an outbreak of poisoning resulting from the ingestion sf cultivated blue mussels (Mytilus edeblis) from a localized area in eastern Canada (Cardigan Bay, Prince Edward Island)was associated with massive blooms of Nitzschia pungens, a widely distributed diatom not previously known to produce toxins; human fatalities resulted. Here we provide proof that the causative agent, dornoic acid, is indeed produced by this diatom. Although no dornoic acid could be detected (<2 ngsrnL-l) in culture medium (FE) prepared from Cardigan River water, it was found in cultures of Nitzschia pungens grown in this medium at concentrations ranging from 0.03 to 0.8 pg-cell-1 in various separate cultures harvested for chemical analysis 7-68 d after inoculation. Vers la fin de 1987, un grand nombre de cas d'empoisonnement par suite de I' ingestion de moules,bleues cultivi'es (Mytilus edu%is) provenant de certaines zones de I'est dar Canada (baie Cardigan, Ile-du-Prince Edouard) ont 6t6 li6es 3 des floraisons massives de Nitzschia pungens, une diatomke largement rkpandue que I'on ne croyait pas produire des toxines. Des di'c6s ssnt survenus. bes auteurs d6msntrent que I'agent respnsable, I'acide dornoVque, est produit par cette diatom&. Bien que I'acide domoi'que n'ait pu Gtre dkeli' (2 ng-mb-l) dans des cultures preparees i3 partir de I'eau de la riviere Cardigan (milieu FE), cet acide a pu &re d6cel6 dans des cultures de Nitzschia pungens ri'alisi'es dans ce milieu a des csncentrations de 0,03 2 Q,8 pg.celll~le-l, ceci dans diverses cultures distinctes prklev4es pour analyse chirnique de 7 21 68 jours aprPs !'inoculation. Received August 3, 1988 Accepted August 22, 1988 8J9826) omoic acid (1) is a naturally occurring amino acid pre- viously isolated from two red algae (Chormdria armaia and Alsidium csraklinum) (Fattomsso m d Piattelli 1988) but unknown in the phytoplankton. It is an excitatory amino acid and probably acts as an agsnist to glutamate, a neurotrans- mitter in the central newsus system, in a manner analogous to kainic acid (2) (Hampson and Weanthold 1988). This toxin was found in cultivated blue mussels (Myii8'busedulis) harvested ~overnber 198'7 from Cadigm Bay in eastern Prince Edwwd Island, Canada (J. %. C. Wright et al., submitted). The three fatalities and over 100 cases of sickness that occurred from the ingestion of these mussels were attributed to dornoic acid poi- soning. Analyses of aqueous extracts of the whole mussel meats gave concentrations (up to 900 pg-g-l in the mussel tissue) sufficient to induce toxic symptoms in humans. Gut contents of mussels from the Cardigan River, P.E.I., where the toxicity was most acute, revealed a preponderance sf Nitzschia! sp. Water samples and concentrates of phytopla&ton showed a monospecific bloom of a chain-forming Mtzschia sp. (99% sf total phgitoplaAton) in concentrations of - f O9 ce1ls.L- com- parable with those found in "red-tide" blooms. The chains of this Nitzsckia sp. were stiff, motile, and had a maximum of 39 cells per chain. The cells were 80-140 pm long, 4.54 prn wide, symmetric, spindle-shaped with pointed ends, and con- tained two chromatophores (Fig. 1). The species was identified as Mtzschia pungens Gmnow f. rnu&tiseries Hasle (Hasle 1965) by M. Poulin (National Museums of Canada, Ottawa, Ont., pers. comrn.) and C. Bird (ARL, gers. comm.) and was con- finned by G. W. Hasle (University sf Oslo, Nowway). Domsic acid was found in the Cardigan River blooms of Nitzschia ppungens providing circumstantid evidence that the source of domoic acid in the mussels was the Nitzschia pkngcpas consumd by the mussels (S. Bates et al., in prep.). The ques- tion of whether the toxin was produced de mvo by Niizschia itself or that the diatom was merely a vector could not be prop- erly addressed until luge quantities of the organism could be cultured. Single chains of Nitzschia pungens cells were isolated from Cardigan Bay water sampled on 16 December f 987, using a modified I-d hypodermic syringe fitted with a finely drawn microhaematoc~t tube. They were washed several times with sterile medium to minimize transfer of contaminating bacteria and other rnicrmrganisrns. Cells were grown at 10°C and Can. J. Fish. Aqwr. Sci., Vo'ol. 45, 1988