Growth, Toxin Production and Allelopathic Effects of Pseudo-nitzschia multiseries under Iron-Enriched Conditions.

In order to assess the effects of Fe-enrichment on the growth and domoic acid (DA) production of the toxigenic diatom , static cultures that received the addition of different iron (Fe) concentrations were maintained for 30 days. Intra- and extracellular DA concentrations were evaluated over time, and growth and chain-formation were compared to those of non-toxic diatoms, sp. Growth rates of (μ = 0.45-0.73 d) were similar among cultures containing different Fe concentrations. Likewise, the similar incidence and length of stepped cell chains (usually 2-4; up to 8-cell long) among the treatments reinforces that the cultures were not growth-inhibited under any condition tested, suggesting an efficient Fe acquisition mechanism. Moreover, DA concentrations were significantly higher under the highest Fe concentration, indicating that Fe is required for toxin synthesis. sp. reached comparable growth rates under the same Fe concentrations, except when the dissolved cell contents from a culture was added. The 50-70% reduction in cell density and 70-90% decrease in total chlorophyll-a content of sp. at early stationary growth phase indicates, for the first time, an allelopathic effect of undetermined compounds released by to another diatom species.