An intimate view into the silica deposition vesicles of diatoms

Christoph Heintze,Bernd Rellinghaus,Jannes Hauptstein,Darius Pohl,Petr Formanek,Nils Kröger

doi:10.1186/s42833-020-00017-8

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.

Highlights

Diatoms are a species-rich lineage of single-celled algae that produce silica-based cell walls with species-specific morphologies
Identifying valve silica deposition vesicle (SDV) in cell lysates For the rapid identification of valve SDVs in cell lysates, we aimed to establish a fluorescent labeling strategy in combination with correlative fluorescence-electron microscopy imaging, which is outlined in the following
To facilitate following the cell cycle progression in vivo, transgenic cell lines were used that expressed C-terminally tagged silicanin-1 (Sin1-GFPC), which was previously shown to be located in the membrane of T. pseudonana valve and girdle band SDVs [32]

Summary

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 [1,2,3,4,5,6,7,8,9]. Diatoms are the prime model systems for Diatom cell walls are constructed from two types of biosilica building blocks termed valves and girdle bands. The girdle bands are partially overlapping rings of silica that are oriented transversely to the long axis of the cylinder constituting a gap-less connection between the two valves. Regarding the nano- and microarchitecture, the biosilica of valves is much more intricately patterned including hierarchical pore patterns, struts, and tubes, while girdle bands are rather flat, perforated rings. Biogenesis of the valves and girdle bands is tightly linked to the cell cycle with valves only being

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