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KTH/Nordita/SU seminar in Theoretical Physics

Understanding the cell shape and locomotion of Spiroplasma

by Dr Martin Lindén (Uppsala University)

FA31 ()


The Spiroplasmas are helical bacteria of the class Mollicutes, that lack cell walls. They swim by propagating a kink of handedness-change along their body. The major structural component of the cell is a multistranded protein ribbon bound to the inner side of the cell membrane. The ribbon runs the entire length of the cell body, following the shortest helical path on the membrane inner surface. Kink propagation is believed to be driven by conformational changes in the ribbon subunits, or by unidentified motor proteins attached to the ribbon, but the microscopic mechanism is unknown.
We combine simple mechanical models with new observations of cell shapes to understand kink propagation in Spiroplasma. Our conclusions differ from earlier work based on purely geometrical considerations. This leads us to propose new microscopic mechanisms for the handedness change, and a new interpretation of the observed bend angle in kinked cells. These results offer a qualitatively new understanding of existing data, as well as suggestions for future experiments.