Abstract
BackgroundThe diatom cell wall, called the frustule, is predominantly made out of silica, in many cases with highly ordered nano- and micro-scale features. Frustules are built intracellularly inside a special compartment, the silica deposition vesicle, or SDV. Molecules such as proteins (silaffins and silacidins) and long chain polyamines have been isolated from the silica and shown to be involved in the control of the silica polymerization. However, we are still unable to explain or reproduce in vitro the complexity of structures formed by diatoms.Methods/Principal FindingIn this study, using fluorescence microscopy, scanning electron microscopy, and atomic force microscopy, we were able to compare and correlate microtubules and microfilaments with silica structure formed in diversely structured diatom species. The high degree of correlation between silica structure and actin indicates that actin is a major element in the control of the silica morphogenesis at the meso and microscale. Microtubules appear to be involved in the spatial positioning on the mesoscale and strengthening of the SDV.Conclusions/SignificanceThese results reveal the importance of top down control over positioning of and within the SDV during diatom wall formation and open a new perspective for the study of the mechanism of frustule patterning as well as for the understanding of the control of membrane dynamics by the cytoskeleton.
Highlights
Diatoms are unicellular algae that make cell walls out of silica which is structured on the nano- to micro-scale in an enormous variety of shapes
Valve formation in another Coscinodiscus species, C. wailesii, was described in detail previously [30], and our observations suggest a similar process of formation in C. granii
Previous TEM examination of C. wailesii suggested that the nucleus was in contact with the forming valve [30]; our results suggest that in C. granii, the nucleus remains more closely associated with the epivalve (Fig. 2)
Summary
Diatoms are unicellular algae that make cell walls out of silica which is structured on the nano- to micro-scale in an enormous variety of shapes. Diatoms range in overall size from two to several hundreds of microns, with detailed and intermediate features ranging from the nanometer to micron scale. Because of their ability to reproducibly form complex three dimensional structures with controlled features at multiple length scales, diatoms are an exceptional model for the study of silica biomineralization and the development of biomimetic approaches for nanoscale materials synthesis. The diatom cell wall, called the frustule, is predominantly made out of silica, in many cases with highly ordered nano- and micro-scale features. We are still unable to explain or reproduce in vitro the complexity of structures formed by diatoms
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