Giant basal spicule from the deep-sea glass sponge Monorhaphis chuni: synthesis of the largest bio-silica structure on Earth by silicatein

Abstract

Like all sponges (phylum Porifera), the glass sponges (Hexactinellida) are provided with an elaborate and distinct body plan, which relies on a filigree skeleton. It is constructed by an array of morphologically determined elements, the spicules. Schulze described the largest siliceous hexactinellid sponge on Earth, the up to 3 m high Monorhaphis chuni, collected during the German Deep Sea Expedition ”Valdivia“ (1898–1899). This species develops an equally large bio-silica structure, the giant basal spicule (3 m × 10 mm). Using these spicules as a model, one can obtain the basic knowledge on the morphology, formation, and development of silica skeletal elements. The silica matrix is composed of almost pure silica, endowing it with unusual optophysical properties, which are superior to those of man-made waveguides. Experiments suggest that the spicules function in vivo as a nonocular photoreception system. The spicules are also provided with exceptional mechanical properties. Like demosponges, the hexactinellids synthesize their silica enzymatically via the enzyme silicatein (27 kDa protein). This enzyme is located in/embedded in the silica layers. This knowledge will surely contribute to a further utilization and exploration of silica in biomaterial/biomedical science.