Figure 4: Mechanical models for B. subtilis multicellular fibres at low and high RH.
From: Study of the tensile properties of individual multicellular fibres generated by Bacillus subtilis

(a) Schematic diagram of cellular indention developed in previous studies15,16. The AFM tip first approaches the outer layer of the cell envelope in the short-axis direction, and then transfers the pressure load from the outer layer to the inner layer. (b) Tensile test of individual fibre in this study. The load is along the long-axis direction of the B. subtilis cell. The cell wall and plasma membrane are simultaneously stretched. (c) Spring model is used to describe the elastic properties of the fibre at low RH; this shows a stress–strain curve of a typical sample and the corresponding linear fitting result at RH = 26%. (d) Kelvin–Voigt model is used to describe the tensile mechanical behaviour of the fibre at high RH; this shows the parameter fitting for a typical sample at RH = 52%. In the inset, the model is shown as a parallel combination of a spring and a dashpot.