Fig. 5: The influence of Si concentration and Si inhibitor in the growth medium on seta formation.

a–d SEM images of cells that were blotted dry for imaging, the insets show live cells. e–h HAADF-STEM images of washed and dried cell walls. The contrast in these images arise from the density of the material and is more affected by the folding of the cell walls then from actual variable densities of the material. Insets in d and h show optical microscopy images of the same cells as in the main panels. The fluorescence of PDMPO, which was added with Ge to the growth medium, allowed the identification of specific valves (indicated with green arrows) that formed in the presence of Ge. These valves do not have setae. For each experimental condition, a statistical summary of the average number and standard deviation of setae is presented below the images. In the different Si concentrations (a–c, e–g), the number of setae declines from a value that is close to the ideal four setae per cell to almost no setae at all. In the Ge-treated culture (d, h), the valves that are labeled with PDMPO, thus the ones that formed in the presence of Ge, have almost no setae, while the unlabeled valves that form prior to Ge addition have the expected two setae per valve.