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Impact of foreign elements on dinoflagellate calcification: biological effects and materials application
Calcium carbonate is the most widespread biomineral produced by many organisms such as corals, molluscs, and foraminifera. Some unicellular microalgae, the calcareous dinoflagellates, produce complex calcite architectures in an extracellular compartment, the so-called outer matrix. Calcite morphogenesis takes place entirely within this outer matrix, and is thus similar to mollusk calcification, but distinct from biomineralisation in intracellular vesicles.
Our group introduced calcareous dinoflagellates as a model system for studying extracellular biomineral morphogenesis in single-celled organisms. Our new biomineralisation model for dinoflagellates demonstrates that biogenesis of the calcitic shell involves an intracellular, disordered mineral precursor phase . To date, there is only limited data on this inorganic calcite precursor and its transformation – the target of my PhD thesis. Amorphous calcium carbonate (ACC) is widespread in biology and plays a crucial role as precursor in calcium carbonate formation . For this reason, we hypothesise that the growth of calcite inside the outer matrix is based on transformation from a hydrated, phosphorus-containing Mg-ACC.
My PhD project assesses the impact of foreign elements on the transformation of an amorphous precursor phase both in vivo in dinoflagellates and in vitro using synthetic ACC. I am using Leonella granifera and Thoracosphera heimii as model species to track the uptake and processing of foreign elements from the seawater via the precursor phase into the shell. These in vivo studies include the cultivation in artificial seawater of different elementary composition, the monitoring of the seawater composition and the analysis of its impact on the calcification process.
In addition, this is supported by in vitro experiments using synthetic amorphous precursors, especially the biologically relevant Mg-P-ACC, and in situ studies of their transformation. Later, the target of my experiments is also the incorporation of zinc, iron, and strontium into ACC and their subsequent transformation into crystalline polymorphs. These in vitro studies provide a synthetic model system that will facilitate the understanding of more complex biological calcification processes.
During my PhD project, I will combine tools from spectroscopy (IR, Raman, and ssNMR), crystallography (XRD), thermal and elemental analysis (TGA, ICP-OES), and microscopy (nano-SIMS and cryo-SEM) for the characterisation of dinoflagellate cells and their calcite shells, synthetic ACC precursors, as well as transformed products.
Overall, this project aims to constrain the influence of foreign cations on ACC precursors and their effect on subsequent phase transformations both in vivo and in vitro.
References: Jantschke, A., Pinkas, I., Schertel, A., Addadi, L., & Weiner, S. (2020). Biomineralization pathways in calcifying dinoflagellates: Uptake, storage in MgCaP-rich bodies and formation of the shell. Acta Biomaterialia, 102, 427-439.  Addadi, L., Raz, S., & Weiner, S. (2003). Taking advantage of disorder: amorphous calcium carbonate and its roles in biomineralization. Advanced Materials, 15(12), 959-970.