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Abstract
The bacterial flagellar motor (BFM) is the molecular machine responsible for the swimming and chemotaxis of many species of motile bacteria. The BFM is bidirectional, and changes in the rotation direction of the motor are essential for chemotaxis. It has previously been observed that many species of bacteria also demonstrate brief pauses in rotation, though the underlying cause of such events remains poorly understood. We examine the rotation of Escherichia coli under low mechanical load with high spatial and temporal resolution. We observe and characterize transient pauses in rotation in a strain which lacks a functional chemosensory network, showing that such events are a phenomenon separate from a change in rotational direction. Rotating at low load, the BFM of E. coli exhibits about 10 pauses s–1, lasting on average 5 ms, during which time the rotor diffuses with net forwards rotation. Replacing the wild type stators with Na+ chimera stators has no substantial effect on the pausing. We discuss possible causes of such events, which are likely a product of a transient change in either the stator complex or the rotor.
Highlights
The bacterial flagellar motor (BFM) is a membrane embedded protein complex that controls the motility and chemotaxis of many species of bacteria
Though transient pauses lasting on the order of tens to hundreds of milliseconds seem to be an inherent feature of the BFM in many species, it was recently reported that the BFM sometimes toggles between maximum and zero speed on a timescale of ms [9]
Using backscattering dark field microscopy [18], we monitored the rotation of 100 nm gold nanoparticles attached to the hook of the BFM of a non-switching strain of E. coli with a resolution of ∼1.5° and ∼10 μs
Summary
The bacterial flagellar motor (BFM) is a membrane embedded protein complex that controls the motility and chemotaxis of many species of bacteria. The rotation speed of the BFM is known to be dependent upon IMF [1, 2], temperature [3], external load [4, 5], and the number of engaged stator protein units [6]. Using backscattering dark field microscopy [18], we monitored the rotation of 100 nm gold nanoparticles attached to the hook of the BFM of a non-switching strain of E. coli with a resolution of ∼1.5° and ∼10 μs. We performed these experiments for motors driven by Na+ chimera stators [19]. We resolve pauses in rotation and characterize the motion of the rotor during these events, and we discuss the potential biological causes and implications
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