Projekt

Certain green algae, the coccolithophorids, form intriguingly beautiful and symmetric calcite scales, the coccoliths. Depending on the algae, the biomineralisation processes range from a biologically induced and mostly extracellular to a biologically controlled intracellular mineral formation. The coccolith formation is genetically controlled and species specific. Studies of biomineralisation from these simple unicellular algae are undertaken because they are expected to give insight in the basic processes believed to govern biomineral formation in general: Supramolecular preorganization, interfacial molecular recognition, vectorial growth regulation and finally cellular processing to higher order architectures [3]. For an understanding of the biomineralisation process, the crystallographic characterization of the 'final product', the coccolith itself is neccessary. Up to now all crystallographic studies of coccoliths were done by light and electron microscopy. Besides advantages like the high spatial resolution and direct imaging, electron microscopy has some disadvantages. Often in large parts coccoliths are not translucent for the electron beam and are prone to severe radiation damage at higher beam currents. Both shortcomings are especially severe when the aim of the diffraction study is the structural interplay between the anorganic crystal and biological macromolecules forming templates for oriented nucleation or serve as 'glue' in composite biomaterials like mollusc shells or teeth enamel. With the advent of microbeam technologies on synchrotron sources diffraction experiments on coccoliths become feasible, comprising mWAXS, mSAXS and mRFA. Microbeam experiments performed at the ESRF beamline ID13 on samples of Braarudosphaera Bigelowii and Coccolithus Pelagicus gave insight into the crystallographic structure of the coccoliths. First small angle data on isolated Braarudosphaera Bigelowii coccoliths indicate, that this experiments may even show the structural interplay of organic material and the crystalline carbonate structure.