Bacterial Flagella and Motility Overview

Study Notes

Bacteria can have single or multiple flagella, which can be located at one or both poles.
Flagellar movement in peritrichous bacteria like E. coli and S. enterica involves rotation in both directions, leading to longer "runs" and short "tumbles".
The direction of movement in bacteria with monotrichous flagella can be reversed by rotating the flagellum in the opposite direction.
The flagellum is composed of around 50 different proteins and has three segments: filament, hook, and basal body.
The flagellar motor, powered by the proton motive force, consists of over 20 proteins anchored in the cytoplasmic membrane and cell wall.
Gram-positive bacteria lack P/L rings in their flagellum and their flagellin filament is made of a single protein called flagellin.
The flagellum is built from the inside out, with flagellin being produced in the cytoplasm and secreted through the hollow filament.
Variations of flagellar motility include the use of Na+ gradient instead of proton motive force, and spirochetes having a flagellum in the periplasm resulting in corkscrew motion.
Taxis is the directed movement of bacteria, achieved using a "bias random walk" and can include chemotaxis, phototaxis, and aerotaxis.
Chemotaxis involves movement in the direction of gradients of specific chemicals, with longer runs and less frequent tumbles if moving towards desirable nutrients.
Other types of motility, such as twitching motility, involve non-flagellar movement, like the use of Type IV pili as a grappling hook.
The text provides links to YouTube videos demonstrating flagella, motility, and chemotaxis in bacteria.