An intimate view into the silica deposition vesicles of diatoms
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BMC Materials Open Access
RESEARCH ARTICLE
An intimate view into the silica deposition vesicles of diatoms Christoph Heintze1, Petr Formanek4, Darius Pohl5, Jannes Hauptstein1, Bernd Rellinghaus5 and Nils Kröger1,2,3*
Abstract Diatoms are single-celled microalgae that produce silica-based cell walls with intricate nano- and micropatterns. Biogenesis of diatom biosilica is a bottom-up process that occurs in large intracellular compartments termed silica deposition vesicles (SDVs). Investigating the mechanisms of silica morphogenesis has so far been severely limited by the lack of methods for imaging the entire volume of an SDV with high spatial resolution during all stages of development. Here we have developed a method that allows for rapid identification and electron microscopy imaging of many different, full sized SDVs that are in the process of producing biosilica valves. This enabled visualizing the development of characteristic morphological biosilica features with unprecedented spatio-temporal resolution. During early to mid-term development, valve SDVs contained ~ 20 nm sized particles that were primarily associated with the radially expanding rib-like biosilica structures. The results from electron dispersive X-ray analysis suggests that the immature biosilica patterns are silica-organic composites. This supports the hypothesis that silica morphogenesis is dependent on organic biomolecules inside the SDV lumen. Keywords: Thalassiosira pseudonana, Cyclotella cryptica, Biosilica, Morphogenesis, Cell wall, Costa, Cribrum pore, Areola pore, Fultoportula, Silica nanoparticle Introduction Diatoms are a species-rich lineage of single-celled algae that produce silica-based cell walls with species-specific morphologies. A characteristic feature of diatom biosilica are hierarchical patterns of pores with diameters from the nano- to the micrometer range. The porous patterns equip diatom biosilica with interesting materials properties, including light capturing and the highest specific strength of any known biological material [1–9]. A rapidly increasing number of genome and transcriptome data from diatoms have become available, and several species are readily amenable to genetic manipulation [10]. Therefore diatoms are the prime model systems for *Correspondence: nils.kroeger@tu‑dresden.de 1 B CUBE, Center for Molecular and Cellular Bioengineering, TU Dresden, 01307 Dresden, Germany Full list of author information is available at the end of the article
studying the molecular basis of biological silica formation, and genetic engineering methods to further enhance the functionalities of diatom biosilica have been established [7, 11, 12]. Diatom cell walls are constructed from two types of biosilica building blocks termed valves and girdle bands. In the cylindrical cell walls of Thalassiosira pseudonana and Cyclotella cryptica, which have been studied in the present work, the valves represent the top and bottom lids of the cylinder. The girdle bands are partially overlapping rings of silica that are oriented transv
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