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Bio-Sintering/Bio-Fusion of Silica in Sponge Spicules

Authors

  • Xiaohong Wang,

    Corresponding author
    1. National Research Center for Geoanalysis, Chinese Academy of Geological Sciences 26 Baiwanzhuang Dajie, CHN-100037 Beijing, (China)
    2. ERC Advanced Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz Duesbergweg 6, D-55128 Mainz, (Germany)
    • National Research Center for Geoanalysis 26 Baiwanzhuang Dajie, CHN-100037 Beijing, (China).
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  • Matthias Wiens,

    1. ERC Advanced Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz Duesbergweg 6, D-55128 Mainz, (Germany)
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  • Ute Schloßmacher,

    1. ERC Advanced Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz Duesbergweg 6, D-55128 Mainz, (Germany)
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  • Klaus Peter Jochum,

    1. Max Planck Institute for Chemistry P.O. Box 3060, D-55020 Mainz, (Germany)
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  • Heinz C. Schröder,

    1. ERC Advanced Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz Duesbergweg 6, D-55128 Mainz, (Germany)
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  • Werner E. G. Müller

    Corresponding author
    1. ERC Advanced Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz Duesbergweg 6, D-55128 Mainz, (Germany)
    • ERC Advanced Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University Mainz Duesbergweg 6, D-55128 Mainz, (Germany).
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  • This work was supported by grants from the European Commission (Project No. 266033 “SPECIAL”; X. H. W. H. C. S, W. E. G. M.), the Bundesministerium für Bildung und Forschung Germany (project “Center of Excellence BIOTECmarin”; W. E. G. M.), the International Human Frontier Science Program (W. E. G. M.), the International S & T Cooperation Program of China (Grant No. 2008DFA00980; X. H. W.), and the Public Welfare Project of Ministry of Land and Resources of the People's Republic of China (Grant No. 201011005-06; X. H. W.). W. E. G. M. is holder of an ERC Individual Advanced Grant (No. 268476 BIOSILICA).

Abstract

The synthesis of siliceous spicules in both demosponges and hexactinellids is enzymatically driven via silicatein. This enzyme exists both intra-spicularly and in the extra-spicular space. It catalyzes the formation of bio-silica constituting the silica lamellae that are formed during the appositional (layer-by-layer) growth of the spicules. The extent of (bio-silica forming) activity of silicatein from the demosponge Suberites domuncula measured in vitro reflects the amount of bio-silica required for the formation of spicules in vivo. It is shown that during growth and maturation of the spicules in demosponges a bio-fusion process occurs that results in an intra-spicular sintering of the silica lamellae to form compact silica rods. The morphological characterization of the globular asters (microscleres) from the demosponge Geodia cydonium revealed that these spherical spicules are formed from a tuft of silicatein filaments which radiate from a common origin. While in demosponges a complete intra-spicular bio-sintering/bio-fusion process occurs, this process is incomplete in hexactinellid spicules. There, only the most inner lamellae of the spicules fuse leaving the more peripheral silica lamellae separate. However, within this class of sponges several families (example Euplectella aspergillum) show a bio-sintering process between individual spicules. There, bio-silica is secondarily deposited onto mature spicules, giving rise to an ordered array of bio-silica bridges. Furthermore we report that for the formation of the strong and stiff bio-silica skeleton of sponges a hardening process is required that is (presumable) driven by cell-membrane bound aquaporin channels which allow the removal of water, released during the bio-silica polycondensation reaction.

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