Abstract
The bacterial flagellum is a helical filamentous organelle responsible for motility. In bacterial species possessing flagella at the cell exterior, the long helical flagellar filament acts as a molecular screw to generate thrust. Meanwhile, the flagella of spirochetes reside within the periplasmic space and not only act as a cytoskeleton to determine the helicity of the cell body, but also rotate or undulate the helical cell body for propulsion. Despite structural diversity of the flagella among bacterial species, flagellated bacteria share a common rotary nanomachine, namely the flagellar motor, which is located at the base of the filament. The flagellar motor is composed of a rotor ring complex and multiple transmembrane stator units and converts the ion flux through an ion channel of each stator unit into the mechanical work required for motor rotation. Intracellular chemotactic signaling pathways regulate the direction of flagella-driven motility in response to changes in the environments, allowing bacteria to migrate towards more desirable environments for their survival. Recent experimental and theoretical studies have been deepening our understanding of the molecular mechanisms of the flagellar motor. In this review article, we describe the current understanding of the structure and dynamics of the bacterial flagellum.
Highlights
Bacterial motility is an extremely intriguing topic from various scientific aspects
Since bacterial motility varies among bacterial species, bacteria utilize their own motility system optimized for their habitats
Because the assembly of the flagellar filament by multiple flagellins affects its mechanistic properties for flagellar function in different environments [26,32,33,34,35], the composition of the flagellar filament structure would be optimized for environmental conditions, in which the bacteria live and survive
Summary
Bacterial motility is an extremely intriguing topic from various scientific aspects. For example, motility can be a crucial virulence attribute for pathogenic bacteria, such as Salmonella enterica (hereafter referred to Salmonella) and Helicobacter pylori [1,2]. E. coli and Salmonella cells rotate can swim in a by bundling left-handed helical filaments behindofthe body (run) when all of them in CCW straight line by bundling left-handed behind the cellfrom bodyCCW (run)towhen all flagellar of them direction. E. CCW coli and CW, the flagellar bundle is disrupted, the cell to tumble and change thesignaling swimming direction. The hook is supercoiled and flexible against bending and acts as a universal joint protofilaments and is divided into at least three structural parts: the rod, the hook and the filament to smoothly transmit produced byrod the is motor to the filament. The filament is normally a left-handed supercoil to act as a helical screw to to produce thrust for swimming motility. The filament undergoes polymorphic transformation from the left-handed supercoil to right-handed ones when bacterial cells tumble and change swimming direction [16]
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