Difference in Bacterial Motion between Forward and Backward Swimming Caused by the Wall Effect

Abstract

A bacterial cell that has a single polar flagellum alternately repeats forward swimming, in which the flagellum pushes the cell body, and backward swimming, in which the flagellum pulls the cell body. We have reported that the backward swimming speeds of Vibrio alginolyticus are on average greater than the forward swimming speeds. In this study, we quantitatively measured the shape of the trajectory as well as the swimming speed. The trajectory shape in the forward mode was almost straight, whereas that in the backward mode was curved. The same parameters were measured at different distances from a surface. The difference in the motion characteristics between swimming modes was significant when a cell swam near a surface. In contrast, the difference was indistinguishable when a cell swam >60 microm away from any surfaces. In addition, a cell in backward mode tended to stay near the surface longer than a cell in forward mode. This wall effect on the bacterial motion was independent of chemical modification of the glass surface. The macroscopic behavior is numerically simulated on the basis of experimental results and the significance of the phenomenon reported here is discussed.

The Selective Value of Bacterial Shape

“…When the curved cells of Vibrio alginolyticus swim near a planar surface, forwardmoving cells run in a straight line but backward-moving cells run in a curved arc or in circles (176,197). What distinguishes the behavior of forward-and backward-running cells is unknown (197).…”

“…When the curved cells of Vibrio alginolyticus swim near a planar surface, forwardmoving cells run in a straight line but backward-moving cells run in a curved arc or in circles (176,197). What distinguishes the behavior of forward-and backward-running cells is unknown (197). Once again the surface is "down" relative to the bacterial cell, but in this case, V. alginolyticus swims in large counterclockwise turns, opposite those of E. coli (197), probably because in backward-moving cells the single flagellum leads and pulls the cells.…”

“…What distinguishes the behavior of forward-and backward-running cells is unknown (197). Once again the surface is "down" relative to the bacterial cell, but in this case, V. alginolyticus swims in large counterclockwise turns, opposite those of E. coli (197), probably because in backward-moving cells the single flagellum leads and pulls the cells. Alternatively, since V. alginolyticus is slightly curved (as are many marine vibrioids) and forms a right-handed helix (11), topology might dictate cellular motion near surfaces.…”

Bacterial flagellum as a propeller and as a rudder for efficient chemotaxis

“…From the published trajectories (7), each reversal typically results in a small change in cell orientation, and thus several reversals appear to be necessary for a significant change in the swimming direction. Backtracking was also observed in a number of single flagellated marine bacteria such as Shewanella putrefaciens, Pseudoalteromonas haloplanktis, and Vibrio alginolyticus, which execute the so-called run-reverse steps when following attractants released from porous beads and from algae (8)(9)(10). A pioneering experiment in V. alginolyticus revealed that the timereversal symmetry in the run and the reverse intervals is broken when the cell swims near a surface.…”

“…A pioneering experiment in V. alginolyticus revealed that the timereversal symmetry in the run and the reverse intervals is broken when the cell swims near a surface. In such a case, although the forward swimming remains more or less straight, the backward trajectory is remarkably curved and often forms a tight circle a few bacterial lengths in diameter (9). This asymmetry in swimming can be explained by a hydrodynamic interaction with the surface that produces a turning (yawing) moment on the cell body (11).…”