Experimental and theoretical investigations will be conducted using two systems: helical Bacillus subtilis macrofibers, and a new material called bacterial thread constructed of long division-suppressed filaments of B. subtilis cells. The major goals will be to define the mechanical properties of the cell walls, to use this information to determine the structural organization of the cell walls, and to provide a basis for understanding the helical shape deformation and growth dynamics of helical macrofibers. Ultimately, in conjunction with other studies currently underway, the interplay of forces in the cell surface will be understood in molecular terms. Measurements of thread/fiber properties will include tests of tension/extension and tension/twist, design of transducers to refine such tests, use of scanning electron microscopy to define helix angles and filament numbers/thread or macrofiber, measurements of ductility and elasticity by use of surface tension forces, measurements of charge effects on mechanical properties, assessment of osmotic pressure contributions, and studies of changes in mechanical properties during digestion by enzymes that cleave components of the cell wall. Theoretical studies will focus on cylindrical shell structure models of individual cell walls, shape deformation models to account for Mendelson and Tilby structures (1,2), investigations of the mechanics of cell pole structures, statistical studies of macrofibers geometry and models of macrofibers formation by writhing/folding.
