Microbeam Fluorescence, Diffraction, and SAXS Imaging of Worm Jaws

Helga C. Lichtenegger
Institute of Materials Science and Technology, E308, Vienna University of Technology, Austria

In contrast to our teeth and bones that are hardened with calcium-based mineral, the mandibles of certain marine sediments worms exhibit quite peculiar hardening strategies involving the incorporation of transition metals. The polychaete worms Glycera and Nereis, for example, use copper and zinc, respectively, to harden the proteinacous matrix of their jaws. Synchrotron SAXS and WAXS experiments revealed that Glycera jaws contain the rare mineral atacamite [Cu2(OH)3Cl], thus representing the first known case of copper biomineralization. The atacamite is organized in mineralized fibers that run parallel to the jaw and reinforce the needle-like jaw tip. It was shown that in addition to the copper mineral the jaw also contains traces of iron, zinc and unmineralized copper compounds. A combination of position resolved synchrotron microfocus techniques such as x-ray fluorescence imaging, microdiffraction and x-ray absorption spectroscopy was used to explore the role of the trace components. It was found that a fraction of copper is present in oxidation state (I), in contrast to the mineral that exclusively contains Cu(II). This may be indicative of an additional, possibly catalytic, role of copper apart from its structural function. Traces of iron occurred spatially correlated with the copper mineral, suggesting a substitution of copper atoms by iron in the atacamite mineral. Zinc was evenly dispersed throughout the jaw matrix, quite in analogy to zinc found in Nereis jaw where non-mineralized zinc serves to cross-link and harden the proteinaceous matrix.