Characterizing the mechanical parameters of the fission yeast cell wall using atomic force microscopy

While the biological and chemical aspects of the yeast cell have been studied in great \ndepth, much less is known about their physical parameters. The fission yeast cell wall is \na dynamic structure that is subject to variable internal forces during the cell division \ncycle. Since fission yeast (Schizosaccharomyces pombe) is used frequently in biology as \na model organism to study higher order eukaryotes, we decided to examine the physical \nproperties of their cell walls. Using an Asylum MFP3D Atomic Force Microscope, we \ncollected force vs. indentation graphs and fit them to exponential and Hertz models using \nIgor Pro software. We took multiple curves at a single point on the cell wall to check for \nthe precision of our measurements, and also examined different cells at different points \nalong the cell wall. We found a characteristic length for each curve using our \nexponential model, and an approximate value for the Young’s modulus of the cell using a \nHertz model. We found an average value of 41.1 ± 7.9nm for after examining a total of \n51 curves. For the elastic moduli, we found a striking difference between those of cells \ngrown to a normal optical density (OD) and those grown to a low OD. The average \nelastic modulus of cells grown to normal concentrations was 7.9 ±4 MPa, while that of \nthe undergrown cells was only 40.1 ±10 kPa. We concluded that the cell wall displays a \nnonlinear response to stress, likely because it is composed of multiple polymer layers.