MEPS 220:83-92 (2001)  -  doi:10.3354/meps220083

Pseudo-nitzschia sp. cf. pseudodelicatissima ‹ a confirmed producer of domoic acid from the northern Gulf of Mexico

Youlian Pan1,3,**, Michael L. Parsons2,**, Mark Busman1, Peter D. R. Moeller1, Quay Dortch2, Christine L. Powell2, Gregory J. Doucette1,3,*

1Marine Biotoxins Program, Center for Coastal Environmental Health and Biomolecular Research, NOAA National Ocean Service, 219 Fort Johnson Road, Charleston, South Carolina 29412, USA
2Louisiana Universities Marine Consortium, 8124 Highway 56, Chauvin, Louisiana 70344, USA
3Marine Biomedical and Environmental Sciences, Medical University of South Carolina, 221 Fort Johnson Road, Charleston, South Carolina 29412, USA
*Corresponding author. E-mail: Present addresses: **Institute for Marine Biosciences, National Research Council, 1411 Oxford St. Halifax, Nova Scotia B3H 3Z1, Canada ***Natural Sciences Division, Marine Science Department, University of Hawaii-Hilo, 200 W. Kawili Street Hilo, Hawaii 96720, USA

ABSTRACT: Domoic acid (DA), a potent neurotoxin, is synthesized by certain members of the ubiquitous marine diatom genus Pseudo-nitzschia. We recently detected elevated concentrations of DA in phytoplankton field samples from the northern Gulf of Mexico. In searching for a possible source of the toxin, we used a receptor-binding assay to detect DA activity in cultures of P. sp. cf. pseudodelicatissima (Hasle) isolated from this region and confirmed its presence in 2 of 7 clones using liquid chromatography coupled with tandem mass-spectrometric detection (LC-MS/MS). Unlike other toxic Pseudo-nitzschia species examined previously (e.g., P. multiseries, P. australis), cellular levels and net production of DA in these clones were highest in the early exponential phase, while the population growth rate was high and cell concentration was low. There was a negative correlation between cellular DA and cell concentration. The maximum cellular DA activity in cultures was 36 fg DA equiv. cell-1. No net toxin production was evident in the stationary phase, yet extracellular DA levels increased markedly during this period to as much as 88% of the total DA in the cultures. Interestingly, these 2 toxic clones were able to enlarge their cell size after the apical axes declined to 15 to 25 µm, and these larger cells had considerably higher levels of DA than the original small cells. This study unequivocally establishes P. sp. cf. pseudodelicatissima as a source of DA in the northern Gulf of Mexico. Moreover, our work suggests that rapidly growing, rather than nutrient-limited, populations of this diatom should yield maximum net DA production rates and DA cell quotas. Thus, the presence of P. sp. cf. pseudodelicatissima cells, even at the low levels of early, rapidly growing bloom stages, can potentially lead to toxic events.1Ž4

KEY WORDS: Pseudo-nitzschia · Domoic acid · Harmful algal blooms · Receptor-binding assay · Gulf of Mexico

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