Diverse and conserved nano‐ and mesoscale structures of diatom silica revealed by atomic force microscopy

Abstract

SummaryAn outstanding example of biological pattern formation at the single cell level is the diversity of biomineral structures in the silica cell walls of the unicellular eukaryotic algae known as diatoms. We present a survey of cell wall silica structures of 16 diatom species, which included all major cell wall components (valves, girdle bands and setae), imaged across the nano-, meso-and microscales using atomic force microscopy. Because of atomic force microscopy's superior ability to image surface topology, this approach enabled visualization of the organization of possible underlying organic molecules involved in mineral structure formation. Diatom nanoscale silica structure varied greatly comparing the same feature in different species and different features within a single species, and frequently on different faces of the same object. These data indicate that there is not a strict relation between nanoscale silica morphology and the type of structure that contains it. On the mesoscale, there was a preponderance of linear structures regardless of the object imaged, suggesting that assembly or organization of linear organic molecules or subcellular assemblies that confine a linear space play an essential and conserved role in structure formation on that scale. Microscale structure imparted an overall influence over nanoand mesoscale structure, indicating that shaping of the silica deposition vesicle plays a key role in structure formation. These results provide insights into the design and assembly principles

Dynamics of silica cell wall morphogenesis in the diatom Cyclotella cryptica: Substructure formation and the role of microfilaments

“…The unstructured portion is the region of girdle band that ''underlaps" with the adjacent girdle band, and it makes logical sense that this would be synthesized first to maintain structural integrity. Recent AFM data (Hildebrand et al, 2009b) coupled with these images (Fig. 7) indicate that girdle bands exhibit similar complexity in their structure and formation processes as some valve structures.…”

“…The detailed structures of girdle bands are rarely imaged (Hildebrand et al, 2006(Hildebrand et al, , 2009b, due to the difficulty of visualizing these thin structures. It is not clear whether the images presented in Fig.…”

“…There are several models for how mesoscale structure may form. It has been proposed that (1) organic molecules serve as organizers of polymerization determinants inside the SDV (Hildebrand, 2008;Hildebrand et al, 2009b;Robinson and Sullivan, 1987), (2) the process occurs through diffusion limited aggregation where the role of organics is limited to providing a confined space (Parkinson et al, 1999), or (3) self assembly of silaffins and polyamines and silacidins (Sumper and Kröger, 2004;Wenzl et al, 2008) or phase separation processes involving polyamine droplets (Lenoci and Camp, 2008;Sumper, 2002) generate higher order structure. Observational data has resulted in the generation of models for mesoscale formation in which cytoskeletal elements located outside the SDV interface with membrane proteins spanning the silicalemma that position silica polymerization determinants inside (Pickett-Heaps et al, 1990;Robinson and Sullivan, 1987).…”

Characterization and Localization of Insoluble Organic Matrices Associated with Diatom Cell Walls: Insight into Their Roles during Cell Wall Formation

“…There is a tendency in diatoms for initial silica deposition to form a base layer of the proximal surface, followed by z-axis growth towards the distal surface [33]. Proximal structures tend to be more highly ordered than distal ones [34], which implies that the organic material controlling structure is associated with, or influences that, surface more. The organic material described by Scheffel et al is likely to correspond to the matrix described in this study, in which case, its silica precipitation activity in the presence of polyamines would be consistent with a role in silica formation in vivo [14].…”

Biosilica and bioinspired silica studied by solid-state NMR

“…Diatoms, unicellular algae abundant both in fresh and sea water, are famous for their complex and versatile silica structured cell walls [38]. The diatoms' cell wall is not only exceptionally beautiful but also functionally important.…”