Tensile properties of individual multicellular Bacillus subtilis fibers

Microfibers formed by Bacillus subtilis (B. subtilis) have attracted interest because of their potential for use as biodegradable fibers. In this work, an efficient method based on the micro-liquid bridge method (LBM) is proposed to investigate the mechanical properties and the deformation evolution in individual fibers. For the first time, tensile testing of fibers of this type containing several cells is conducted in a scanning electron microscope (SEM) chamber and the in situ deformation evolution of the fibers and the septa is observed. Experimental results show that these fibers are almost broken at the positions of the septa at low humidity, but also show that their fracture morphologies are different. At high humidity, local necking deformation occurs at the septum position. To explore the deformation mechanism of an individual bacterial fiber with a diameter of several hundred nanometers under different humidity conditions, we use the finite element method (FEM) to analyze the tensile deformation behavior of these fibers when their septa are at various separation levels. The numerical results indicate that weak interactions among the septa lead to the dispersion of both the fibrous tensile strength and the modulus. These results may be helpful in understanding the deformation mechanism, thus leading to further improvements in the mechanical performance of these fibers.