Iron and copper limitations differently affect growth rates and photosynthetic and physiological parameters of the marine diatom Pseudo-nitzschia delicatissima

Abstract

In ~ 50% of the ocean, iron (Fe) limits phytoplankton growth, including that of the diatom Pseudo-nitzschia. Fe-limited Pseudo-nitzschia spp. may produce the potent neurotoxin domoic acid (DA) to access Cu, needed at the core of a high-affinity Fe transport system. To test this hypothesis, we investigated the growth, physiology, and DA production of P. delicatissima under Fe limitations, Cu starvation, and Fe and Cu co-limitations. Compared with the control, Fe limitation decreased chlorophyll content by up to 86% and quantum yield (QY) by 3.6-fold. Severe Fe limitation decreased esterase activity by 60% and maintained lipid content, while mild Fe limitation increased both esterase activity and lipid content by 23% and 100%, respectively. Cu starvation increased chlorophyll content, lipid content, and esterase activity by 76%, 303%, and 47%, respectively, with QY being identical to replete cells. Co-limitations induced modifications close to, but significantly different from, Fe limitations. P. delicatissima produced no DA during these experiments. In this species, the Cu demand for Fe acquisition may be low relative to other cellular Cu pools or this species may not use Cu to uptake Fe. © 2013, by the Association for the Sciences of Limnology and Oceanography, Inc.