Fig. 2: Density profiles of the apical and subapical regions of isolated sacculi.

Cryo-electron tomographic slices of S. coelicolor WT, ΔcslA and ΔmatAB, sacculi, either treated with HF and non-treated, were used to analyze the density of the cell wall. For each sacculus, the apical region (red) together with the subapical regions on the left (dark gray) and right side (light gray) were segmented and straightened in the XY plane. The density was determined by averaging pixel values (arbitrary units) along the straightened cell-wall regions, and normalized against the background pixel values. These pixel values are presented in the density plots relative to the distance perpendicular to the cell wall (a). Representable cryo-ET fractions of the segmented and straightened cell walls in the XY plane are depicted in the panels below the density plot of each strain (b). Not all sacculi contain a left and right subapical region in the tomogram field of view, as depicted by the missing panel in the ΔmatAB. For each sacculus, the area under the curve (AUC) of the density plot was determined, at which the AUC of the apical region was normalized with the AUC of subapical region (left and right averaged, if both available) and plotted in c. Hence, the value of 1 indicates that the apical and subapical region are comparable in terms of cell-wall density, whereas a value deviating from 1 indicates a denser (<1) or less dense (>1) apical cell-wall region. The normalized AUC of each sacculus is depicted as a single dot, the horizontal line depicts the group average (WT n = 2, WT + HF n = 5, ΔcslA n = 5, ΔcslA + HF n = 5, ΔmatAB n = 4, ΔmatAB + HF n = 6).