engleski

Nanomechanical mapping of marine diatom in seawater

It is generally accepted that a diatom cell wall is characterized by a siliceous skeleton covered by an organic envelope essentially composed of polysaccharides and proteins. Understanding of how the organic component is associated with the silica structure provides an important insight into the biomineralization process and patterning on the cellular level [1]. We have selected weakly silicified, pennate marine diatom Cylindrotheca closterium in order to study structure and morphology of its cell wall by probing the nanomechanical properties of the two compositionally and morphologically different regions using a novel AFM imaging mode (Peak Force Tapping [2]). The unique characteristics of Cylindrotheca spp. cell wall are regions which are believed to be completely unsilicified. This makes them ideal candidates for studying structure and organization of organic and inorganic domains of cell wall. First, we performed a detailed morphological analysis from whole cell down to nanoscale and compared imaging in air and in seawater. Extracellular polymer (EPS) were visualized as fine fibers and networks at the molecular level using mica substrate in air [3]. The nanomechanical properties were measured over the entire cell surface in seawater at a resolution that was not achieved previously. While fibulae and girdle bands (mostly silica) were found to be stiffer, showing less indentation, valve structures were slightly softer and showed more complex structure. After acid treatment, we identified 15 nm sized silica spheres in the valve region. The silica spheres were neither fused together nor forming a nanopattern. A cell wall model is proposed with individual silica nanoparticles incorporated in an organic matrix. Such organization of girdle band and valve regions enables the high flexibility needed for different movement modalities and adaptation to different environments while maintaining the integrity of the cell.

atomic force microscopy (AFM); Cylindrotheca closterium; deformation; diatom cell wall; elasticity; marine diatom; nanomechanical properties; Peak Force Tapping AFM; Young’s modulus

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