title: First evidence of the presence of chitin in skeletons of marine sponges. Part II. Glass sponges (Hexactinellida: Porifera).
abstract: Sponges (Porifera) are presently gaining increased scientific attention because of their secondary metabolites and specific skeleton structures. In contrast to demosponges, whose skeletons are formed from biopolymer spongin, glass sponges (hexactinellids) possess silica-organic composites as the main natural material for their skeletal fibres. Chitin has a crystalline structure and it constitutes a network of organized fibres. This structure confers rigidity and resistance to organisms that contain it, including monocellular (yeast, amoeba, diatoms) and multicellular (higher fungi, arthropods, nematodes, molluscs) organisms. In contrast to different marine invertebrates whose exoskeletons are built of chitin, this polysaccharide has not been found previously as an endogenous biopolymer within glass sponges (Hexactinellida). We hypothesized that glass sponges, which are considered to be the most basal lineage of multicellular animals, must possess chitin. Here, we present a detailed study of the structural and physico-chemical properties of skeletal fragments of the glass sponge Farrea occa. We show that these fibres have a layered design with specific compositional variations in the chitin/silica composite. We applied an effective approach for the demineralization of glass sponge skeletal formations based on an etching procedure using alkali solutions. The results show unambiguously that alpha-chitin is an essential component of the skeletal structures of Hexactinellida. This is the first report of a silica-chitin's composite biomaterial found in nature. From this perspective, the view that silica-chitin scaffolds may be key templates for skeleton formation also in ancestral unicellular organisms, rather than silica-protein composites, emerges as a viable alternative hypothesis.
authors.affiliation: Max Bergmann Center of Biomaterials, Institute of Materials Science, Dresden University of Technology, Dresden, Germany. hermann.ehrlich@mailbox.tu-dresden.de
authors.forename: Hermann
authors.initials: H
authors.lastname: Ehrlich
authors.forename: Manfred
authors.initials: M
authors.lastname: Krautter
authors.forename: Thomas
authors.initials: T
authors.lastname: Hanke
authors.forename: Paul
authors.initials: P
authors.lastname: Simon
authors.forename: Christiane
authors.initials: C
authors.lastname: Knieb
authors.forename: Sascha
authors.initials: S
authors.lastname: Heinemann
authors.forename: Hartmut
authors.initials: H
authors.lastname: Worch
mesh_terms: D000818:Animals; D002686:Chitin / Q000032:analysis* / Q000648:ultrastructure; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D011161:Porifera / Q000737:chemistry* / Q000648:ultrastructure; D012822:Silicon Dioxide / Q000032:analysis; D017550:Spectroscopy, Fourier Transform Infrared
chemical_list: D002686:Chitin; D012822:Silicon Dioxide