Probing 3D Chemotaxis Response of Aliivibrio fischeri  by Single-cell Phase Contrast Imaging
Xiang-Yu Zhuang1*, Chien-Jung Lo1
1Department of physics, National Central University, Taoyuan, Taiwan
* Presenter:Xiang-Yu Zhuang,
Bacteria modulate their flagellar motor rotational direction to perform chemotaxis. In principle, it is a two-states modulation preforming random-walk and bias random walk.  Classical example is that peritrchous bacteria swim by rotating flagella that forms a bundle when the flagellar motors turn in the counterclockwise (CCW) direction. When one or more motors rotate in a clockwise (CW) direction, the bundles spread out and the bacteria tumble. After the CCW rotation of the flagellar motor is restored, a new swimming direction will be selected. By adjusting the interval between CCW and CW according to the signal protein CheY after phosphorylated by the kinase CheA in the bacteria chemotaxis system, cells can migrate towards the attractant or away from the repellent.
However, swimming patterns are very different in monotrichous and lophotrichous bacteria due to polar flagellar distribution. In order to reveal the underlining mechanisms, we investigate swimming and chemotaxis behaviors of the polar multi-flagellated marine bacteria A. fischeri in the aqueous medium. Using 3D bacteria tracking on a phase contrast microscope, we can precisely reconstruct detail natural  trajectories of swimming bacteria in complex 3D environments. By analyzing the trajectories of A. fischeri,  the chemotaxis mechanism from single-cell to population-level can be revealed.

Keywords: Aliivibrio fischeri, phase contrast imaging, single-cell tracking, swimming pattern, chemotaxis