Controls on Domoic Acid Production by the Diatom Nitzschia pungens f. multi series in Culture: Nutrients and lrradiance" S. s. Bates" Department of Fisheries and Oceans, Gulf Fisheries Centre, P.O. Box 5030, Moncton, N.B. f/C 9B6, Canada A. S. W. de Freitas and j. E. Milley Institute for Marine Biosciences, National Research Council of Canada, 1411 Oxford St., Halifax, N.S. B3H 3ZI, Canada R. Pocklington Department of Fisheries and Oceans, Bedford Institute of Oceanography, P.O. Box 1006, Dartmouth, N.S. B2Y 4A2, Canada M. A. Quilliam Institute for Marine Biosciences, National Research Council of Canada, 1411 Oxford St., Halifax, N.S. B3H 3ZI, Canada and J. c. Smith and J. Worms Department of Fisheries and Oceans, Gulf Fisheries Centre, P.O. Box 5030, Moncton, N.B. f/C 9B6, Canada Bates, S. S., A. S. W. de Freitas, j. E. Milley, R. Pocklington, M. A. Quilliam, j. C. Smith, and j. Worms. 1991. Controls on domoic acid production by the diatom Nitzschia pungens f. multiseries in culture: nutrients and irradiance. Can. j. Fish. Aquat. Sci. 48: 1136-1144. Nitzschia pungens f. multiseries (clone NPARL) was grown in nonaxenic batch culture under a range of growth conditions. Domoic acid (DA) was not detected during exponential growth, but production promptly started at a rate of approximately 1 pg DA'cell- 1 ·d- 1 atthe onset of the stationary phase, in this case induced by silicate limitation. Cellular DA reached a maximum of 7 pg-cell": thereafter, DA production continued at the same rate, with cellular levels remaining relatively constant due to concurrent releaseof DA into the culture medium. DA production ceased in the absence of nitrogen during the stationary phase, but resumed when nitrate was added back to the medium. Low irradiance slowed the division rate and consequently delayed the attainment of the stationary phase, but DA production rates were comparable with the control once stationary phase was reached. Cells during the dark period of a light-dark cycle, or placed into darkness, or in the presence of the photosynthetic inhibitor DCMU promptly ceased DA production. We conclude that at least three conditions are required for DA production by clone NPARL: cessation of cell division, availability of nitrogen during the sta- tionary phase, and the presence of light. Growth in medium f/2 fulfils these requirements. On a effectue la culture discontinue non axenique de la diatornee Nitzschia pungens f. multiseries (clone NPARL) dans diverses conditions de croissance. On n'a pas releve la presence d'acide dornolque (AD) pendant la phase de croissance exponentielle, mais la production a commence sans tarder au taux d'environ 1 pg AD'cellule- 1 'jour- 1 des Ie debut de la phase de croissance stationnaire, provoquee dans ce cas-ci par la penurie de silicate. La concentration cellulaire d' AD a atteint un maximum de 7 pg-cellule ": par la suite, la production d' AD s'est poursuivie au rnerne taux et lesteneurs cellulairessont derneurees relativement constantes etant donne la liberation sirnultanee d'AD dans Ie milieu de culture. Laproduction d'AD a cesse en I'absence d'azote pendant la phase stationnaire, mais a recommence apres ajout de nitrate au milieu de culture. Un faible eclairement a ralenti Ie taux de division des cellules et par consequent la realisation de la phase stationnaire, mais les taux de production d'AD etaient com parables a ceux obtenus dans Ie cas de la culture ternoin une fois la phase station- naire atteinte. Des cellules placees a l'obscurlte, exposees a la phase obscure d'un cycle jour-nuit, ou mises en presence d'un inhibiteur de la photosynthese, Ie DCMU, ont rapidement cesse toute production d' AD. Lesauteurs formulent la conclusion que Ie clone NPARL requiert au moins trois conditions pour la production d'AD, soit I'absence de la division cellulaire, la disponibilite d'azote pendant la phase stationnaire et la presence de lumiere. La croissance en milieu de culture f/2 satisfait a ces trois conditions. Received October 3, 1990 Accepted March 8, 1991 (lA778) T he pennate diatom Nitzschia pungens forma multiseries (Hasle 1965) has bloomed for at least the past four autumns in the Cardigan Bay region of eastern Prince 'Contribution No. NRCC 31959. 2Author to whom correspondence should be addressed. 1136 Rec;u Ie 30 octobre 1990 Accepte Ie 8 mars 1991 Edward Island (P.E.I.), Canada (Smith et al. 1989, 1990a, 1990b). This diatom was the primary source of the neurotoxin domoic acid (Wright et aI. 1989; Bates et al. 1989), which con- taminated cultured blue mussels (Mytilus edulis) and resulted in 107 cases of human poisoning and three deaths in 1987 (Perl et aI. 1990). Amnesic shellfish poisoning (ASP) results from Can. J. Fish. Aquat. Sci., Vol. 48,1991