CHANGES IN DOMOIC ACID PRODUCTION AND CELLULAR CHEMICAL-COMPOSITION OF THE TOXIGENIC DIATOM PSEUDO-NITZSCHIA MULTISERIES UNDER PHOSPHATE LIMITATION

Production of domoic acid (DA) a neurotoxin, by the diatom Pseudo-nitz schia multiseries (previously Nitzschia pungens f. multiseries) Hasle and its cellular chemical composition were studied in phosphate-limite d chemostat continuous cultures and in subsequent batch cultures. Unde r steady-state chemostat conditions, DA production increased from 0.01 to 0.26 pg DA . cell(-1). d(-1) as the growth rate decreased. When th e nutrient supply was discontinued (to produce a batch culture), DA pr oduction was enhanced by a factor of ca. 3. DA production was temporar ily suspended upon addition of phosphate to the batch cultures but res umed 1 d later at a higher rate coincident with the decline of phospha te uptake. In both steady-state continuous culture and batch culture, more DA was produced when alkaline phosphatase activity (APA) was high . The association of high DA production with high levels of APA and hi gh cellular N:P ratios strongly suggests that phosphate limitation enh ances DA production. Also, DA production was high when other primary m etabolism (e.g, uptake of carbon, nitrogen, phosphorus and silicon, an d cell division) was low, but chlorophyll a and adenosine triphosphate were generally high. This suggests that the synthesis of DA requires a substantial amount of biogenic energy.