The effect of Fe and Cu on growth and domoic acid production by Pseudo-nitzschiamultiseries and Pseudo‐nitzschia australis

Abstract

Toxigenic pennate diatoms of the genus Pseudo-nitzschia produce domoic acid (DA), the neurotoxin linked to amnesic shellfish poisoning. We investigated how Fe and Cu affect growth and DA production by P. multiseries and P. australis clones isolated from Monterey Bay, California. Growth rates of these species could be inhibited by both Fe limitation (pFe 20.5, ϭ 50% max ) and Cu toxicity (pCu 10.5, ϭ 30-50% max ). The rate of DA production during the exponential phase was a significant inverse function of cellular growth rates (P Ͻ 0.02). Voltammetric measurements of dissolved DA-equivalents in short-term experiments indicated that the cellular production of DA increased from ϳ5 amol DA cell Ϫ1 h Ϫ1 under optimal growth conditions to ϳ40 amol DA cell Ϫ1h Ϫ1 under Fe-deficient conditions and ϳ105 amol DA cell Ϫ1 h Ϫ1 under Cu-stressed conditions. The DA was released to the medium under metal stress conditions, with intracellular DA concentrations decreasing relative to nonstressed cells. Fe uptake rates by P. multiseries were slow compared to other marine diatoms in the absence of dissolved DA but were enhanced threefold (P Ͻ 0.03) by adding DA to the medium. DA addition also partially alleviated toxic Cu conditions. Our findings suggest that DA production during exponential growth of these two toxigenic Pseudo-nitzschia species is directly induced by Fe-deficient or Cu stress conditions and that 95% of this DA is actively released into the medium. Changing trace metal conditions in coastal waters therefore may have a profound effect upon intracellular DA concentrations and thereby influence the toxic effect of these harmful bloom events.Fewer than two dozen of the more than 5,000 known marine phytoplankton species produce powerful toxins that affect food webs (Taylor 1990), although blooms of these toxic species appear to be increasing worldwide (e.g., Smayda 1992; Anderson 1995). Until recently, only planktonic dinoflagellates were recognized to produce algal toxins. However, a deadly outbreak of the diatom Pseudo-nitzschia mul-1 Current address: Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, British Columbia V6T 1Z4 Canada.2 Corresponding author.Acknowledgments M. Wells particularly extends his great appreciation to K. W. Bruland for generously sharing his insights on marine biogeochemistry over several years and, in particular, for his observation that domoic acid could be a metal chelator and thus be related to bioactive metal availability. We also especially thank N. Towers and I. Garthwaite (AgResearch, New Zealand) for kindly providing us reference dissolved domoic acid determinations by their immunoassay assay (cELISA). We also thank S. Bates for his suggestions and thoughtful comments on an earlier version of this manuscript.

Induction of domoic acid production in the toxic diatom Pseudo-nitzschia seriata by calanoid copepods

“…Maldonado et al (2002) found that P. multiseries and P. australis produced DA during the exponential growth phase in iron-deficient or toxic copper concentrations. Almost all (95%) of the DA produced was released into the medium and the authors concluded this to be a stress reaction against unfavorable micronutrient levels (Maldonado et al, 2002). In the present study, ∼60% of the total DA produced (cellular and dissolved) by P. seriata in physical contact with C. hyperboreus was released into the medium.…”

“…nutrients in relation to the growth phase (reviewed in Bates, 1998;Lelong et al, 2012), pH (e.g. Lundholm et al, 2004), and trace metal limitation or toxicity (Maldonado et al, 2002). Evidence of allelopathic effects of DA, however, has not been found (Lundholm et al, 2005).…”

Southern Ocean phytoplankton physiology in a changing climate

“…Furthermore, both OA and temperature can affect biological growth and generation of organic ligands, potentially favouring growth of specific phytoplankton species and inducing a shift in the community structure unrelated to Fe (e.g., Tortell et al, 2008a;Trimborn et al, 2014). As different biological communities excrete different iron-binding ligands (Trick and Wilhelm, 1995;Maldonado et al, 2002;Hassler et al, 2015;Norman et al, 2015), a shift in community structure or changes in Fe-stress could have a greater impact on Fe chemistry and bioavailability than those associated with changes in temperature and pH (Gledhill et al, 2015). However, the effect that the modulation of the excretion of organic ligands associated with basal biological activity or the change in the nature of organic ligands associated with a shift in community will have on Fe chemistry and bioavailability is yet to be investigated.…”

Domoic acid uptake and elimination kinetics in oysters and mussels in relation to body size and anatomical distribution of toxin

“…Although Pseudonitzschia cells can release relatively large amounts of DA in the water column, especially under macronutrient- (Bates, 1998)o r iron-limitation (Maldonado et al, 2002), only minor toxin incorporation (0.3-0.6% of available DA in 5-24 h) has been reported from the dissolved phase by mussels Novaczek et al, 1991). Fast photodegradation (Bouillon et al, 2006) may further limit the availability of dissolved DA to marine organisms.…”