Abstract
The influence of a rigid boundary and a free boundary on the motion of singly flagellated bacteria is experimentally investigated. The speed of backward swimming cells is faster near the rigid or free boundary than in the free space without boundary. It is also found that backward swimming speed is faster than forward near the rigid or free boundary. The trajectory of the cells swimming backward near a rigid or free boundary comprises circular parts, while most of forward swimming cells have straight trajectories. Backward swimming cells tend to gather on a rigid or free boundary rather than forward swimming cells. These asymmetric characteristics between forward and backward motions close to a rigid boundary has been predicted by a fluid dynamic simulation.
