Bacterial turgor pressure can be measured by atomic force microscopy

We report a study of the deformability of a bacterial wall with an atomic f orce microscope (AFM). A theoretical expression is derived for the force ex erted by the wall on the cantilever as a function of the depths of indentat ion generated by the AFM tip. Evidence is provided that this reaction force is a measure for the turgor pressure of the bacterium. The method was appl ied to magnetotactic bacteria of the species Magnetospirillum gryphiswalden se. Force curves were generated on the substrate and on the bacteria while scanning laterally. With the mechanical properties so gained we obtained th e spring constant of the bacterium as a whole. Making use of our theoretica l results we determined the turgor pressure to be in the range of 85 to 150 kPa.