Swarming Motility Without Flagellar Motor Switching by Reversal of Swimming Direction in E. coli.

Zhengyu Wu,Rui He,Junhua Yuan,Rongjing Zhang

doi:10.3389/fmicb.2020.01042

Abstract

In a crowded environment such as a bacterial swarm, cells frequently got jammed and came to a stop, but were able to escape the traps by backing up in their moving course with a head-to-tail change (a reversal). Reversals are essential for the expansion of a bacterial swarm. Reversal for a wildtype cell usually involved polymorphic transformation of the flagellar filaments induced by directional switching of the flagellar motors. Here we discovered a new way of reversal in cells without motor switching and characterized its mechanisms. We further found that this type of reversal was not limited to swarmer cells, but also occurred for cells grown in a bulk solution. Therefore, reversal was a general way of escaping when cells got jammed in their natural complex habitats. The new way of reversal we discovered here offered a general strategy for cells to escape traps and explore their environment.

Highlights

Bacteria with peritrichous flagella, such as Escherichia coli, swim in aqueous environment by rotating flagella, each driven by a direction-switchable rotatory motor at its base (Berg, 2003)
One way was to spray water on the surface directly, which was proved to be a way to partially restore swarming motility of S. typhimurium and E. coli with cheY (Wang et al, 2005; Ford et al, 2018)
By adding suitable concentration of the surfactant Tween 20 to swarm plate, we found that the cheY mutant strain HCB1736 could swarm on the Eiken agar surface

Summary

Introduction

Bacteria with peritrichous flagella, such as Escherichia coli, swim in aqueous environment by rotating flagella, each driven by a direction-switchable rotatory motor (flagellar motor) at its base (Berg, 2003). The direction of motor rotation determines the bacterial swimming mode. When all motors rotate counterclockwise (CCW), their flagella form a bundle, and the cell swims smoothly (called “run”) (Berg and Anderson, 1973; Silverman and Simon, 1974; Macnab, 1977). When one or more motors switch to clockwise (CW) rotation, the associated flagella escape from the bundle while the cell turns to a new direction, producing a “tumble” (Turner et al, 2000). The polymorphic forms can switch from one to another, when motor switches between CCW and CW (Turner et al, 2000)

Methods

Results

Conclusion