Research Starter Grant: Cellular Biomechanics of Bacillus subtilis

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Many bacteria are cylindrical, although a simplistic view of the bacterial cell, taking into account the turgor pressure within the cell, would suggest that all bacterial should be roughly spherical in shape. How do rod-shaped bacteria achieve and maintain their morphology? This question will be addressed using physical analysis and mathematical modelling, taking into acount what is known of bacterial biochemistry and organization. The cell wall is composed predominantly of a polymer mesh of peptidoglycan that separates the inside of the cell from the outside of the cell and provides structural rigidity. Directly inside the peptidoglycan is a bilayer membrane. The cell maintains a turgor pressure such that the inside of the cell is at a higher pressure than outside the cell. Therefore, a simple picture of cell morphology would be that the peptidoglycan forms an elastic layer that encloses this pressure difference, much like a balloon. This, however, does not account for the cylindrical shape of the cell, as the pressure difference would drive the peptidoglycan layer toward a more spherical form. Recent experiments from another laboratory suggest that actin-like polymer proteins located just inside the cell membrane may play a crucial role in maintaining cylindrical form in some bacteria, such as Bacillus subtilis. Those experiments also suggest a molecular mechanism that could drive the supercoiling behavior that has been observed in macrofibers of B. subtilis and a number of other filamentous cylindrical bacteria. This research project will explore the connection between helical polymer proteins located at or near the cell membrane and the elasticity of the cell wall in order to probe the role these proteins play in maintaining cellular form, examine whether they could be the molecular cause of supercoiling, and suggest further experiments to test these hypotheses.Broader Impacts: This is a Research Starter Grant, awarded to an NSF Postdoctoral Fellow who has accepted a tenure-track position at an eligible institution, as described in NSF 99-142. Dr. Wolgemuth will actively integrate research and education and foster cross-disciplinary training by recruiting a biology graduate student to work on this project.