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Structures and silica forming properties of insoluble organic matrices from diatomsPawolski, Damian 31 August 2018 (has links)
Since the 18th-century scientists are studying diatoms, fascinated by their beauty and
diversity. Their nano- and micropatterned biosilica cell walls are outstanding examples of
biologically controlled mineral formation. Although the knowledge about diatom cell wall
formation increased over the last 60 years, the process is still far away from being completely
understood. Diatom cell walls exhibit highly interesting material properties, making them
appealing to material scientists. Due to those properties, diatom cell walls are on the brink of
becoming powerful tools in nanotechnology. However, the production of tailored silica
structures for nanotechnology requires a much better understanding of the processes and
components involved in cell wall morphogenesis. Recent studies set the focus on insoluble
organic matrices as important parts of this process, suggesting that they act as templates in
silica morphogenesis. Therefore, in this study, the occurrence of insoluble organic matrices
and their possible silica precipitation activity was analyzed in the three diatom species T.
pseudonana, T. oceanica and C. cryptica.
For all three species girdle band and valve derived insoluble organic matrices could be
identified. The extracted insoluble organic matrices exhibited structural features present in the
corresponding biosilica cell walls. The highest similarities were found in the valve derived
matrices of C. cryptica. Accessibility studies showed that the biosilica associated insoluble
organic matrices of T. pseudonana were only partially accessible, arguing for an entrapment
of insoluble organic matrices in the silica, rather than an attachment to the surface of the cell
wall. All examined insoluble organic matrices of the three species exhibited intrinsic silica
precipitation activity. The most intriguing structures were formed by the insoluble organic
matrices of C. cryptica, yielding a porous silica pattern. The addition of biosilica derived
soluble components or long-chain polyamines promoted this process and moreover lead to the
reconstitution of biosilica-like hierarchical silica pore patterns. The generated silica structures
were templated by the underlying structure of the insoluble organic matrix.
The result presented in this thesis make this the first study reporting the in vitro
generation of diatom biosilica-like hierarchical silica pore patterns using all natural cell wall
components. It supports the hypothesis of microplates acting as templates for biosilica
morphogenesis and introduces an interesting experimental setup for silica-based in vitro
studies on the mechanism of pore formation in diatoms.
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Shedding light on silica biomineralization by comparative analysis of the silica-associated proteomes from three diatom speciesSkeffington, Alastair W., Gentzel, Marc, Ohara, Andre, Milentyev, Alexander, Heintze, Christoph, Böttcher, Lorenz, Görlich, Stefan, Shevchenko, Andrej, Poulsen, Nicole, Kröger, Nils 05 April 2024 (has links)
Morphogenesis of the intricate patterns of diatom silica cell walls is a protein-guided process, yet to date only very few such silica biomineralization proteins have been identified. Therefore, it is currently unknown whether all diatoms share conserved proteins of a basal silica forming machinery, and whether unique proteins are responsible for the morphogenesis of species-specific silica patterns. To answer these questions, we extracted proteins from the silica of three diatom species (Thalassiosira pseudonana, Thalassiosira oceanica, and Cyclotella cryptica) by complete demineralization of the cell walls. Liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis of the extracts identified 92 proteins that we name ‘soluble silicome proteins’ (SSPs). Surprisingly, no SSPs are common to all three species, and most SSPs showed very low similarity to one another in sequence alignments. In-depth bioinformatics analyses revealed that SSPs could be grouped into distinct classes based on short unconventional sequence motifs whose functions are yet unknown. The results from the in vivo localization of selected SSPs indicates that proteins, which lack sequence homology but share unconventional sequence motifs may exert similar functions in the morphogenesis of the diatom silica cell wall.
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