Growth and domoic acid content of Pseudo-nitzschia australis isolated from northwestern Baja California, Mexico, cultured under batch conditions at different temperatures and two Si:NO 3 ratios

Abstract

Domoic acid (DA) poisoning in the southern part of the California Current System has been associated typically with blooms of Pseudo-nitzschia australis. The environmental variables that promote growth and DA production in the Mexican part of this system have not been identified. The present study investigated the effect of temperature and two nutrient ratios on the growth characteristics and DA content of two (BTS-1, BTS-2) P. australis strains isolated from the Pacific coast of northern Baja California peninsula, México. Of the different temperatures assayed (10, 12, 14, 15, 18 and 20 °C), the maximum cell abundance was detected at 12 °C for BTS-2 and 14 °C for BTS-1. The highest maximum specific growth rate (1.69 day −1) was measured at 15 °C for BTS-2. With the exception of cells maintained at 15 °C, growth characteristics were similar in P. australis cultured in a high Si:NO 3 (2.5) or low Si:NO 3 (0.5) ratio at each temperature. Dissolved (dDA) and cellular (cDA) DA content measured at the stationary phase of growth was similar in cells cultivated at the different temperatures. No difference in cDA (between 0.11 and 1.87 pg DA cell −1) was observed in cells cultivated at the two nutrient ratios. To evaluate if P. australis accumulates DA (cDA + dDA) at different stages of the culture and not only during the stationary phase of growth, the BTS-1 strain was cultivated at 14 °C and the content of this toxin was measured during culture development. The cultures were maintained at high (HL; 200 μmol quanta m −2 s −1) and low light (LL; 30 μmol quanta m −2 s −1) and in the two nutrient ratios to evaluate the effect of these variables on DA content. The photosynthetic performance and pigment concentration were measured as indicators of the physiological condition of the cells. cDA was detected in all culture conditions and during the different stages of growth. The highest DA content was measured during the lag phase of growth and it was present mainly in the medium (dDA = 70.83 pg DA cell −1). Cells cultivated at HL produced more DA than LL cultured cells. P. australis cultured in HL presented lower photosynthetic rates than LL cells and had similar concentrations of photoprotective pigments and the highest maximum photosynthetic rates were detected during the lag phase of growth in all culture conditions. The results demonstrate that P. australis from northern Baja California peninsula presents a narrow temperature range for optimal growth under batch culture conditions. P. australis produce DA at different stages of growth, and DA content was related to the light intensity at which the cells were cultivated.