Vivian Merk1 Derk Joester1

1, Northwestern University, Evanston, Illinois, United States

An intriguing question in biomineralization is as how living organisms build smoothly curving single crystals that are perfectly adapted to their biological function. While intensive research has been dedicated to CaCO3 single crystal formation, as in in sea urchins or coccolithophores, many other biominerals remain rather poorly understood. Sulfate biominerals (BaSO4, SrSO4), as found in desmid green algae, are promising candidates for bioremediation of strontium-90 radioisotopes from nuclear waste 1 2.
A prime example of biological single crystal engineering is the delicate endoskeleton in the single-celled protozoa Acantharea that typically consists of 20 spicules of single crystalline celestite (SrSO4) 3. While for each species, spicule shape and arrangement follows a stereotypical pattern, there are very significant differences between species. In addition, the deviation of the spicule habit from equilibrium morphology of SrSO4, and strong crystallographic orientation indicate exquisite control over the crystal growth process. In many other systems a variety of ions, small molecules, and biomacromolecules are thought to play a role in controlling phase transformations, stabilize metastable amorphous intermediates, guide crystal growth, and modulate mechanical properties. We are working to explore the role of such additives in celestite biomineralization.
Towards this goal, we investigated the single-crystalline structure of Acantharea spicules using synchrotron powder XRD and laboratory single-crystal single crystal diffraction. We will further report on an in-depth characterization of the biominerals composition, using synchrotron-based X-ray fluorescence microscopy and atom probe tomography. Finally we will discuss results from electron-optical methods and confocal Raman microscopy that we used to investigate the distribution of organic matter in the biomineral and at the inorganic/soft tissue interface.

1. M. R. Krejci, L. Finney, S. Vogt, D. Joester, Selective Sequestration of Strontium in Desmid Green Algae by Biogenic Co-precipitation with Barite. ChemSusChem 2011, 4 (4), 470-473.
2. M. R. Krejci, B. Wasserman, L. Finney, I. McNulty, D. Legnini, S. Vogt, D. Joester, Selectivity in biomineralization of barium and strontium. Journal of Structural Biology 2011, 176 (2), 192-202.
3. J. R. Wilcock, C. C. Perry, R. J. P. Williams, R. F. C. Mantoura, Crystallographic and morphological studies of the celestite skeleton of the acantharian species Phyllostaurus siculus. Proceedings of the Royal Society Series B-Biological Sciences 1988, 233 (1273), 393-405.