Cell-kinematics and the swimming motility of an individual bacterium
Bin Liu (Brown University), Thomas Powers (Brown University), Kenneth Breuer (Brown University)
Hydrodynamics of Swimming Microorganisms
Tue 9:00 - 10:30
Barus-Holley 191
We trace individual motile microorganisms using a digital 3D tracking microscope in which the microscope stage follows the motion of the target so that it remains focused at the center of the view-field. Through this technology, we not only trace a single cell over extended duration with submicron accuracy but also explore its detailed cell kinematics simultaneously. We apply this tracking microscope to a study of the motion of an individual Caulobacter crescentus, a bacterium that moves up to 100 microns (or 50 body lengths) per second and reverses its direction of motion occasionally by switching the rotation direction of its single helical flagellum. The cell body of the bacterium has a crescent shape, which also counter-rotates to balance the torque, with its detailed kinematics captured by high-speed imaging. We show that when the cell reverses the rotation direction of the right-handed flagellum, e.g., switching from CW (a pusher) to CCW (a puller), its cell-kinematics is not completely reversible. In case of a puller, the cell almost spins along its long axis. However, in case of a pusher, besides spinning, the cell body precesses along its swimming direction, following a helical trajectory. These two types of cell-kinematics contribute to distinguishable cell motilities between a pusher and a puller: the pusher rotates relatively slower at same swimming speed. We also show that the cell motility depends on the detailed swimming speed, and varies from one individual to others. We try explaining such varieties by correlating them to the variations in cell-kinematics.