Comparative Study of Adaptation of Eukaryotic Marine Phytoplankton to Iron Limitation

Understanding of the connections between iron and marine phytoplankton is critical for predicting ecosystem changes in future ocean. Yet the mechanisms of adaptation to iron limitation by marine microalgae are still poorly understood. Most of the studies are based on investigations of single species, or field samples that are problematic to interpret. Interspecific relationships in the marine ecosystem are complex and it is difficult to predict which phytoplankton species would be advantaged over others with predicted changes in the ocean chemistry. So there is a need for lab-scale experiments under standardized conditions including a spectrum of significant, well-characterized model species. Here we present such study focused on a comparative analysis of the strategies to cope with iron limitation and evaluation of interspecific competition as a function of iron availability. For this we have chosen species that cover a range of ecological niches, considering several aspects: ecological relevance, blooming potential, cultivation conditions, differences in iron requirements, and our experimental experience. These include harmful dinoflagellate Amphidinium carterae, model Rhizaria Bigelowiella natans, euglenid Eutreptiella gymnastica, widespread coccolithophore Emiliania huxleyi, oceanic diatom Thalassiosira oceanica, model diatom Phaeodactylum tricornutum. Using different biochemical and biophysical methods we have compared iron acquisition and utilization in these species and investigated how iron availability influences their photosynthetic parameters. Moreover, we have established a co-cultivation system with different combinations of model phytoplankton species where, within the reasonable timeframe required to observe the effect of nutritional changes, each species in the consortium is distinguishable by flow cytometry and present in quantities enabling to study the effect of changing iron availability at both physiological and molecular level.