Sponge Biosilica Formation Involves Syneresis Following Polycondensation in vivo

Abstract

Syneresis is a process observed during the maturation/aging of silica gels obtained by sol-gel synthesis that results in shrinkage and expulsion of water due to a rearrangement and increase in the number of bridging siloxane bonds. Here we describe how the process of biosilica deposition during spicule ("biosilica" skeleton of the siliceous sponges) formation involves a phase of syneresis that occurs after the enzyme-mediated polycondensation reaction. Primmorphs from the demosponge Suberites domuncula were used to study syneresis and the inhibition of this mechanism. We showed by scanning electron microscopy that spicules added to primmorphs that have been incubated with manganese sulfate fuse together through the deposition of silica spheres and bridges. Energy-dispersive X-ray mapping of the newly formed deposits showed high silicon and oxygen content. These biosilica deposits contain a comparably higher percentage of water than mature/aged spicules. Quantitative real-time polymerase chain reaction analyses revealed that the addition of silicate to primmorph cultures resulted in a marked upregulation of the expression of the aquaporin gene and of the genes encoding the silica anabolic enzyme silicatein-α and the silica catabolic enzyme silicase. On the other hand, addition of manganese sulfate, either alone or together with silicate, caused a strong reduction in the level of aquaporin transcripts, although this metal ion did not essentially affect the silicate-induced increase in silicatein-α and silicase gene expression. We conclude that the secondary silica deposits formed on spicules under physiological conditions in the presence of silicate fuse together and subsequently undergo syneresis, which is facilitated by the removal of water through aquaporin channels. In growing spicules, these processes of biosilica formation and syneresis in the lamellar monolithic structures precede the final step of "biosintering" during which the massive biosilica rods of the spicules are formed.

Acquisition of Structure-guiding and Structure-forming Properties during Maturation from the Pro-silicatein to the Silicatein Form

“…The values determined are about 1000-fold lower than those measured for spicules formed in vivo. The decreased flexibility of natural spicules can be attributed to a hardening process (48), for which a process of syneresis had been attributed to. A detailed description of the process of syneresis had been given recently (48).…”

“…The decreased flexibility of natural spicules can be attributed to a hardening process (48), for which a process of syneresis had been attributed to. A detailed description of the process of syneresis had been given recently (48). It had been outlined that the reaction water, which accumulates during the polycondensation of ortho-silicate to polysilicate in the extracellular space, is removed by an aquaporin-driven cellular process (48); Fig.…”

Effect of Bioglass on Growth and Biomineralization of SaOS-2 Cells in Hydrogel after 3D Cell Bioprinting

“…Biosilica was prepared enzymatically by using, in a reaction volume of 1 mL, 200 µM prehydrolyzed TEOS and 20 µg/mL of recombinant silicatein in 50 mmoles/L Tris/HCl buffer (pH 7.4; 150 mmoles/L NaCl, 0.5% [w/v] PEG [polyethylene glycol]). PEG was added to the reaction in order to harden the biosilica formed [29], [30]. The enzymatic reactions were performed at 22°C for up to 120 min with agitation.…”

The silicatein propeptide acts as inhibitor/modulator of self‐organization during spicule axial filament formation

“…As an example, in the siliceous sponge Geodia cydonium , both microscleres (< 10 μm) and megascleres (> 10 μm) exist, with a spatially distinct occurrence, positioning and morphology . The spicules interact both functionally and morphologically , and provide the sponge specimens with a backbone or scaffold, allowing them to reach their final size and morphology . In siliceous demosponges, the spicules remain separated from each other and are connected via organic linkers that were identified as DUF (domain of unknown function) molecules , while in siliceous hexactinellids, the spicules secondarily fuse together via silica bridges .…”