Effects of silicate limitation on production of domoic acid, a neurotoxin, by the diatom Pseudo-nitzschia multiseries. II. Continuous culture studies

Abstract

Production of domoic acid (DA) by Pseudo-nitzschia multiseries (Hasle) was studied using continuous cultures with growth rdtcs ranging from 0 06 to 0.67 d-' At steady states, DA concentrations were 1.65 to 553.20 pg 1-' and production rates were 0 007 to 1.354 pg DA cell-' d-' Both were negatively correlated with rates of growth and silicate uptake. DA production was studled further by stopping the addition of fresh medium, thus producing batch mode experiments, in some of which silicate was allowed to decline, while in another silicate was increased to 85 pM. In those where silicate declined, DA production increased by a factor of 3. The maximum production rate attained was 3.17 pg DA cell-' d-' and the highest DA concentration in the culture was 768.5 1. 19 DA I-'. of which 664 pg 1. ' was in the cells (1 1.9 pg DA cell-'). In the experiment where silicate was enriched. DA production was suspended soon after the enrichment, but resumed when silicate in the medium became low. The results suggested differences in kinetics of DA production and growth under different supply rates of slhcate. There appear to be 2 types of conditions associated with DA production. When dissolved silicate is moderately low and there is a decline in overall physiological activity, intnnsic factors probably trigger the formation of a moderate amount of DA When dissolved silicate IS severely limiting, the extrinsic stress leads to considerably enhanced production of DA. 1989). During these blooms, silicate concentration in the sea water was low (<2 PM; Subba Rao et al. 1988), but the bloom population survived and produced the neurotoxin domoic acid.In batch culture, the production of domoic acid (DA) by Pseudo-nitzschia nlultiseries generally occurs in the stationary phase when cell division has stopped (Subba Rao et al. 1990, Bates et al. 1991 or when growth of the culture populations decline due to silicon limitation (Pan 1994). Pan et al. (1996 -this issue) proposed that DA product~on can be divided into 2 stages: the first coincides with the late exponential phase when growth proceeds slowly, and the second occurs when silicate in the medium is depleted and the culture is in the stationary phase. The rates of DA production during the second stage (13.67 to 30.20 fg DA cell-' d-l) were an order of magnitude higher than those during the first stage (0.97 to 4.98 fg DA cell-' d-l). This implies that (1) toxin production is not necessarily associated with complete cessation of cell division, and (2) this diatom produces more DA when cells are under severe silicate stress. 0

Effect of pH on growth and domoic acid production by potentially toxic diatoms of the genera Pseudo-nitzschia and Nitzschia

“…In both instances, nutrient limitation or some other factor has been considered responsible (see Bates 1998). The production and concentration of DA in both medium and cells in the present study reached levels similar to those recorded in previous laboratory experiments ( Bates et al 1991, Bates 1998.Scenarios where nutrients were not limiting but production of DA did occur have been described previously (see Bates et al 1993, Pan et al 1996c. A possible explanation for these scenarios could be elevated pH.…”

Diatom Transcriptional and Physiological Responses to Changes in Iron Bioavailability across Ocean Provinces

“…Interestingly, concentrations of domoic acid (DA), a neurotoxin produced by Pseudo-nitzschia, was 90 pg mL −1 in initial seawater (T 0 ) and exceeded 3,000 pg mL −1 in the control treatment by T 1 (Supplementary Figure 3). This increase in DA concentration may be linked to both the increase in Pseudo-nitzschia abundance and depletion of Si(OH) 4 resulting in Si-limited cells which has been shown to greatly enhance DA production (Pan et al, 1996).…”

Pseudo-nitzschia Peragallo (Bacillariophyceae) diversity and domoic acid accumulation in tuberculate cockles and sweet clams in M’diq Bay, Morocco

“…This difference of contamination between spring and autumn could be explained by both the difference in environmental conditions during spring and autumn periods and the differences in Pseudo-nitzschia species composing blooms. The production of DA is dependent on the concentration of nutrients (PAN et al 1996, KLEIN et al 2010). …”