Figure 9. Transmission electron microscopy of the cell wall upon overexpression of the PGA22 and PGA59 genes.

Overexpression strains for PGA22 and PGA59 and the SC5314 control strain were grown overnight in YPD in the presence or absence of 50 µg.mL⁻¹ doxycycline and the structure of their cell wall analyzed by transmission electron microscopy. Representative images of the cell wall of the three strains are shown in (A) and allow visualization of the cell wall inner layer containing the skeletal polysaccharides chitin, β-1,3-gucan and β-1,6-gucan, and the cell wall fibrillar outer layer enriched with O-linked and N-linked mannose polymers (mannans) covalently associated with GPI-anchored proteins attached to the β-1,3-gucan skeleton. The black arrow highlights the reduced outer layer in the PGA22-overexpression strain. (B) Inner cell wall thickness and (C) Outer fibrils length; Data are average measurements taken for 30 individual cells of each strain and standard error of means are shown. Significant results according to Student's t-tests are represented on the top of each bar (asterisk); *** p≤0.001.