Colloquium: November 26, 2014
Roland G. Winkler*
Physics of Bacteria Locomotion
|November 26, 2014 Wednesday||15:40||EE01|
Host: Giovanni Volpe
ABSTRACT — Cell motility is a major achievement of biological evolution and is essential for a wide spectrum of cellular activities. Microorganisms, such as spermatozoa, bacteria, protozoa, and algae, use flagella — whip-like structures protruding from their bodies — for their propulsion. Swimming of uni- and multi-cellular organisms is essential for their search for food (chemotaxis), the reaction to light (phototaxis), and the orientation in the gravitation field (gravitaxis). Furthermore, flagellar motion plays a major role in higher organisms, where they transport fluid in the respiratory system in form of cilia, are involved in cellular communications, and even determine the morphological left-right asymmetry in the embryo. Unicellular swimmers, e.g., bacteria like Escherichia coli, are typically of a few to several ten micrometers in size. The physics ruling the swimming on this micrometer scale is very different from that applying to swimming in the macro-world. Swimming at the micrometer scale is swimming at low Reynolds numbers, where viscous damping by far dominates over inertia. In the evolutionary process, microorganisms acquired propulsion strategies, which successfully overcome and even exploit viscous drag. The flagella of E. coli are rotated by a motor located in the cell membrane. During swimming, the flagella self-organize into a helical bundle and rotate with the same frequency. A change in the swimming direction is achieved by stopping or reversing the rotation direction of one or several flagella, a movement denoted as run-and tumble motion. The bundle formation requires the synchronized rotation of the individual flagella, which is governed by hydrodynamic interactions. In the talk, the importance of hydrodynamics for bacteria locomotion will be discussed and illustrated by theoretical and mesoscale hydrodynamic simulation results. Both, the swimming behavior of individual cells in bulk and at surfaces as well as collective effects will be addressed.
*Forschungszentrum Jülich GmbH, Jülich, Germany
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