Figure 1.
Frustule and chain morphology.
(A) A schematic structure of the frustule (modified after [1]). The frustule consists of two overlapping elements, or thecae, that fit together like the two halves of a Petri dish. Each theca is capped with a distinctive structure called a valve. A series of thin, overlapping bands of silica, termed girdle elements (or girdle bands), extends from the rim of the valve forming the sidewall of the theca. The two thecae are identically shaped but differ slightly in diameter; one fits within the other, with their girdle elements partially overlapping, to form an enclosed structure around the cell's protoplasm. The frustule is perforated with nanometer-scale pores arranged in species-specific, ornate patterns that allow the exchange of solutes between the cell and the environment. (B) A light-microscope image of L. undulatum. (C) SEM image of L. undulatum. (D) Epifluorescence image of L. undulatum after staining with PDMPO. The green region indicates a valve and marginal ridges that were formed during the incubation time with PDMPO.
Table 1.
A comparison between AFM estimated of the elastic modulus of diatoms.
Figure 2.
Measuring the stiffness of the cell using indentation type experiments.
Averaged force distance curves for deflection of the cantilever (reference on a glass slide; red curve) and for a cell (black curve) measured in the marginal ridge (A) and valve (B) regions. To set the tip-sample contact point (Z0) to a distance of zero, the curves were shifted along the Z-axis. Approximately 100 consecutive curves were acquired for each experiment. The indentation depth is defined as the difference between the Z position of the cell and cantilever deflection at a given loading force. The Young's modulus of the sample was determined by fitting the data with the Hertz model (see Methods).
Figure 3.
A box-and-whisker plot of the Young's modulus (E) as a function of location on the chains (girdle n = 15 samples; valve mantle-girdle transition n = 31 samples; valve edge n = 21 samples; marginal ridge n = 25 samples).
On each box, the central gray line marks the median value, the edges of the box are the 25th and 75th percentiles, and the whiskers extend to the most extreme data points the algorithm considers not to be outliers.
Figure 4.
Frequency distribution of Young's moduli (E) for stained and unstained structural components.
Data were grouped into 3 ‘stiffness’ categories. Number of samples in each category: 0.3<E<0.99 MPa n = 20; 1<E<2.99 MPa n = 32; E>3 MPa n = 37.