Chemotaxis and Flagella Rotation in Bacteria

Chemotaxis Driven by Flagella Rotation

• Flagella can move in two ways: clockwise (CW) or counterclockwise (CCW) rotation.
• The direction of flagella rotation is influenced by the concentration of a substance that the bacteria is attracted to.

Motility and Chemotaxis

• Normal movement of bacteria is composed of runs and tumbles.
• Chemotaxis is a response to different chemical gradients, where bacteria compare the chemical state of the environment to that sensed seconds before and move up or down the gradient accordingly.
• By altering the CW:CCW ratio, bacteria can move up or down the gradient.

Flagella Antigens and Phase Variation

• Salmonella spp. are typed by their O (LPS) and H (flagellar) antigens.
• There are over 2000 serotypes of Salmonella spp. due to different O and H antigens.
• Phase variation allows bacteria to differentially express protein antigens as either phase 1 or phase 2.

Flagellar Structure

Flagellar Basal Body

• The basal body is anchored in the cytoplasmic membrane and cell wall.
• The basal body consists of a small rod passing through a system of rings.
• Gram-negative bacteria have multiple rings, including an outer ring in the outer membrane/LPS, one in peptidoglycan, one in the cytoplasmic membrane, and one in the cytoplasm.
• Gram-positive bacteria have one fewer inner ring.

Flagellar Motor

• Two Mot (motor) proteins are anchored either side of the MS ring.
• The Mot proteins drive the flagellar motor, causing a torque that rotates the filament.
• The Fli proteins act as a motor switch.
• Energy is supplied by the passage of protons from outside the cell into the cytoplasm via the basal body mot complex.

Flagella Genetic Control

• Over 40 genes are necessary for motility in E. coli and S. typhimurium.
• The genes are grouped into fla, fli, and flg.
• These genes have several functions, including structural proteins, exporting of flagellar components, and biochemistry of synthesis.

Flagella Motility

• Flagella enables movement at a rate of up to 60 cell lengths per second.
• Movement is different in polar and peritrichous flagella.

Peritrichous

• Movement occurs in a straight line with counter-clockwise rotation.
• Tumbling occurs with clockwise smooth swimming.

Polar

• More rapid spinning occurs.

Flagella

• Flagella are long, thin appendages that originate from the cytoplasmic membrane and extend through the cell wall into the surrounding medium.
• They enable bacteria to be mobile.
• Flagella are very thin (20nm) and not visible by light microscope unless stained.

Flagellar Arrangement

• Monotrichous flagella have one flagellum (e.g., Vibrio cholerae).
• Lophotrichous flagella have multiple flagella on one end (e.g., Bartonella bacilliformis).
• Amphitrichous flagella have flagella at both ends (e.g., Spirllum serpens).
• Peritrichous flagella cover the surface of the bacteria (e.g., Escherichia coli).

Flagellar Structure

• Flagella have a fundamental helical structure with a constant distance between adjacent curves (wavelength).
• The wavelength is constant for a given organism.
• Flagella are composed of protein subunits of flagellin.

This quiz explores the mechanisms of chemotaxis in bacteria, including the role of flagella rotation and attractant concentration. It covers the different types of flagella movement and how they respond to changes in attractant concentration.