A new simple method for quantification and locating P and N reserves in microalgal cells based on energy-filtered transmission electron microscopy (EFTEM) elemental maps
Fig 1
Scheme of the processing of EFTEM N- and P-maps.
The method of EFTEM maps processing may be implemented via two alternative workflows. The workflow “A” (left column) is used for processing N-maps and low-phosphorus maps (less than 10 PRIs per cell section), the workflow “B” (right column) is used for processing P-maps with more than 10 PRIs per cell section. The workflows are based on comparison of the a posteriori probability that a map pixel contains payload information and the Gaussian a priori probability of that the pixel belongs to noise. The difference is expressed as relative entropy value for each pixel so pixels with positive relative entropy values grouped in the right half of the histogram do not belong to the noise. After the relative entropy analysis of each pixel and subsequent binary thresholding of the map, a simple assessment of the relative area and localization of the inclusions on the cell section is carried out. STI−total pixel area of the cell inclusions, Scell−total pixel cell area, SR−relative area of P or N reserves. See text and S1 and S2 Appendices for details.