Dissolved Domoic Acid Does Not Improve Growth Rates and Iron Content in Iron-Stressed Pseudo-Nitzschia subcurvata

Jana K Geuer,Scarlett Trimborn,Florian Koch,Tina Brenneis,Bernd Krock,Boris P Koch

doi:10.3389/fmars.2020.00478

Abstract

Many regions of Antarctica are classified as high nutrient low chlorophyll (HNLC) areas. In these, iron availability is limiting primary productivity and subsequent carbon export. Domoic acid (DA) has previously been detected in the Southern Ocean and suggested to act as a ligand that facilitates iron assimilation for Pseudo-nitzschia spp., species that contribute to Antarctic diatom blooms. An incubation experiment using the Antarctic species Pseudo-nitzschia subcurvata was performed in Antarctic seawater at low and high iron concentrations. Dissolved DA was added to one set of each of the two treatments. This was done to verify whether DA positively affects the growth of the non-toxic species Pseudo-nitzschia subcurvata and increases its cellular iron content, particularly under low iron conditions. We hypothesize that (i) DA is taken up under low iron conditions (ii) that more iron is taken up if DA is available and (iii) that the growth rate increases in the presence of DA. We showed that P. subcurvata did not take up any added DA, even under low iron conditions. Additionally and contrary to our hypothesis, the cells were not positively influenced by the addition of dDA in terms of growth rate, cellular iron and carbon content. Hence, there was no significant difference in iron content between the different treatments. However, the cellular copper content increased under low iron conditions when DA was added. This study suggests that dissolved DA in naturally occurring concentrations does not increase bioavailability of iron to P. subcurvata and that only species producing DA might benefit from it.

Highlights

Marine and terrestrial primary production, contribute to global net primary production (Field et al, 1998)
dissolved inorganic carbon (DIC) and pH did not show any significant differences between the treatments (p > 0.05, Table 2). dissolved DA (dDA) was below detection in non-amended controls but could be almost fully recovered in the different incubations of P. subcurvata, to which Domoic acid (DA) was added (Table 2), with a recovery rate for dDA of 92 ± 2% for treatment +DA and 89 ± 4% for treatment +FeDA
The P. subcurvata used in this experiment did not produce DA, but our results indicate that copper might be useful for iron limited cells in that they better access it when dDA was added to the medium

Summary

Introduction

Marine and terrestrial primary production, contribute to global net primary production (Field et al, 1998). Phytoplankton fix marine carbon (Falkowski, 1994), a process which requires nitrogen and phosphorous (Redfield, 1958), as well as trace elements such as iron, manganese, zinc, copper, cadmium, cobalt, and molybdenum (Quigg et al, 2003). Iron is a important trace element as it is involved in many metabolic pathways including. DA Influence on Iron-Stressed Diatoms respiration and photosynthesis (Geider and La Roche, 1994). One of the most important limiting factors for phytoplankton growth in the SO is iron availability (Martin et al, 1990; De Baar et al, 1995). Iron bioavailability critically depends on its chemical speciation and resulting solubility (Boye et al, 2001). The speciation of iron can control phytoplankton community composition (Trimborn et al, 2017) with some phytoplankton species possessing more efficient mechanisms to adapt to low iron concentrations than others (Meyerink et al, 2017; Bender et al, 2018)

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