223 White beam phase contrast synchrotron micro-tomography on skeleton parts of marine organisms B. Mayzel 1) , P. Zaslansky 2) , A. Rack 3) 1) Dept. of Zoology, Faculty of Life Sciences, Tel Aviv University, Israel 2) Department of Biomaterials, Max Planck Institute of Colloids and Interfaces, Potsdam, Germany 3) Forschungszentrum Karlsruhe GmbH/K.I.T., Institute for Synchrotron Radiation – ANKA, Germany Sponges are marine organisms that secrete mineral and or protein structures that give them a variety of three-dimensional shapes. Most Demospongiae produce silica skeletons or frameworks [1]. These are made of individual spicules ranging in size from micrometers to centimeters. The main role of spicules is the formation of the sponges’ skeleton. This skeleton gives the sponge its shape and general body plan. It also allows it to endure forces such as currents and waves. Spicules can also be used to anchor the sponge to the substrate, as seen in Euplectella and other Hexactinellids. Another role of sponge spicules is defense against predation [2]. A novel ability of silica spicules is the transmission of light along the spicule, much like an optical fiber [3]. Spicules of sponges from the class Demospongiae are made of hydrated amorphous silica. Silica is initially polymerized and deposited in nanospheres or nanoparticles that fuse to each other during spicule formation. The silicified spicules are deposited around an axial organic filament [4]. It has been suggested that these axial filaments act as a template that directs silica deposition. The axial filament is made up mainly of proteins called “silicateins”. These proteins act both as a framework and to catalyze the polymerization of silica [5]. The spicule core surrounding the axial filament in Demospongiae is either triangular or hexagonal in shape. It has been suggested that this is due to the spiral packing of the protein units along the spicule axis [6]. As part of a PhD project, we are studying the structure of the silica spicules of demosponges. Currently we are interested in studying the structure of the spicule core and the axial filament that is found in it. Mainly, characterizing the shape and size of the core throughout the whole spicule. This will enable us to create a three dimensional model of the spicule showing structural layers and internal as well as external details. In this way we hope to resolve a number of questions. The first is the possibility of a spiral structure of the core with a characteristic „pitch“. This could be a species specific structure or specific to a certain spicule type that may be found in a number of different sponge species. Once the structure of the spicule core is determined it will be possible to compare it to known structures of the axial filament proteins. Establishing a direct link between structure of the mineralization template and the final product of the mineralization process will advance our understanding of spicule formation in demosponges. Until now we have been able to produce only single images of spicule cross sections. These were produced by a lengthy process that involves embedding the spicules in epoxy, cutting the sections using a diamond saw and polishing the cross sections Figure 1: a) Light microscope cross-section of a spicule sample (scale bar 25 μm), b) Light microscope cross-section of a spicule sample (scale bar 15 μm), c) SEM scan of spicule (scale bar 500 nm), d) microtomography reconstruction of spicule at 0.9 μm pixel size done at ANKA’s TopoTomo beamline. The arrows point at the spicule’s core.