The effects of cell sizes, environmental conditions, and growth phases on the strength of individual W303 yeast cells inside ESEM

We performed in situ measurements of mechanical properties of individual W303 wild-type yeast cells by using an integrated environmental scanning electron microscope (ESEM)-nanomanipulator system. Compression experiments to penetrate the cell walls of single cells of different cell sizes (about 3-6 mu m diameter), environmental conditions (600 Pa and 3 mPa), and growth phases (early log, mid log, late log and saturation) were conducted. The compression experiments were performed inside ESEM, embedded with a 7 DOF nanomanipulator with a sharp pyramidal end effector and a cooling stage, i.e., a temperature controller. ESEM itself can control the chamber pressure. Data clearly show an increment in penetration force, i.e., 96 +/- 2, 124 +/- 10, 163 +/- 1, and 234 +/- 14 nN at 3, 4, 5, and 6 mu m cell diameters, respectively. Whereas, 20-fold increase in penetration forces was recorded at different environmental conditions for 5 mu m cell diameter, i.e., 163 +/- 1 nN and 2.95 +/- 0.23 mu N at 600 Pa (ESEM mode) and 3 mPa (HV mode), respectively. This was further confirmed from quantitative estimation of average cell rigidity through the Hertz model, i.e., ESEM mode (3.31 +/- 0.11 MPa) and HV mode (26.02 +/- 3.66 MPa) for 5 mu m cell diameter. Finally, the penetration forces at different cell growth phases also show the increment pattern from log (early, mid, and late) to saturation phases, i.e., 161 +/- 25, 216 +/- 15, 255 +/- 21, and 408 +/- 41 nN, respectively.