Physics Colloquium
Friday, April 2th, 2004 4 P.M.

Greg Huber

University of Massachusetts, Boston

Flagella, flip flops, and fluid dynamics at the scale of bacteria.

E. coli and other bacteria manage to swim because of the subtle dynamics of their multiple, rotating, helical flagella. They bundle and de-bundle as their rotary motors episodically change rotational direction. When the flagella are bundled, the bacterium moves linearly, but the dissolution of the bundle leads to a tumbling event that effectively randomizes the cell's orientation. The motor reversal that initiates the tumbling not only torques the flagella oppositely, but also, remarkably, reverses the chirality of the filament, turning a left-handed helix into a right-handed helix. How far can dynamical models go toward understanding this complex phenomenon? I'll give a progress report on our work in this area, and also discuss its application to studying "bacterial carpets", i.e. arrays of motile bacteria that are attached to two-dimensional surfaces. Proper modeling and understanding of the fluid flows produced by carpets is the key to designing microfluidic technologies based on them, such as the controllable movement of micron-sized objects within microfluidic circuits, and micro- and nano-mixers.