An intimate view into the silica deposition vesicles of diatoms

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.

Precision of fiducial marker alignment for correlative super‐resolution fluorescence and transmission electron microscopy

“…Current hypotheses suggest an underlying organic matrix, potentially generated by protein and other biomolecule self-assembly, which drives the nanoscale biosilica formation. Interestingly, dissolution of the silica of isolated biosilica cell walls, leaves behind an insoluble organic, nano-patterned matrix visible in TEM [28,29]. In order to address the question if particular proteins can be associated with particular biomineral structures, sCLEM is a promising tool.…”

Exocytosis of the silicified cell wall of diatoms involves extensive membrane disintegration

“…Diatom cell wall formation is genetically controlled and under strict biological regulation [3][4][5][6] . Silicification is usually an intracellular process, taking place inside a membrane-bound organelle, the silica deposition vesicle (SDV) [7][8][9] . The chemical environment inside the SDV, and the cellular regulation over its contents and shape, exert tight control over the silicification process, resulting in highly specific and reproducible cell wall architectures [10][11][12][13][14] .…”

A protease-mediated switch regulates the growth of magnetosome organelles in Magnetospirillum magneticum

“…For instance, matrix vesicles serve as initial sites for mineral formation in the growth plate and most other vertebrate mineralization tissues (3). Vesicles also play a central role in the formation of calcitic spicules in sea urchins (4), extracellular calcitic plates in marine coccolithophores (5), and the silica-based cell walls of diatoms (6). Compartmentalization within a membrane is believed to provide an isolated microenvironment and a template for efficient nucleation, growth, and shaping of minerals.…”