123 LE 2

• Bacterial Movement

  • Swarming: multicellular surface movement powered by rotating helical flagella
  • Swimming: powered by flagella, individual movement in liquid
  • Twitching: surface movement powered by retraction and extension of Type IV pili
  • Gliding: active surface movement; does not require a flagella or pili
  • involves focal adhesion complexes
  • Sliding: passive surface translocation powered by growth and facilitated by a surfactant
• Flagella

  • function by rotation to push the cell through a liquid medium
  • free at one end and attached at the other end of the cell
  • Tuft: group of flagella
• Flagellar Position

  • Peritrichous: spread throughout the cell
  • Polar: one flagella on either pole
  • Lophotrichous: multiple flagella on either pole
• E. coli is a peritrichously flagellated gram-negative bacterium
• Flagellar Structure

  1. Filament: hollow, rigid cylinder made up of flagellin
  2. Hook region: made up of FlgE protein subunits controlled by C ring and its binding sites
  3. Basal Body: consists of small central rod inserted to a system of rings
  4. penetrates after the LPS up to the cytoplasmic membrane (gram-negative)
• System of Rings

  1. L Ring: first ring upon the hook; located after the LPS
  2. P Ring: located in the peptidoglycan layer (in the periplasm)
  3. MS Ring: located on the outermost part of the cytoplasmic membrane, after the periplasm
  4. C Ring: lowest; after the cytoplasmic membrane
• In gram-positive, only the MS ring and the C ring are present
• Protein Structure of Flagella

  • Mot proteins: generates torque; anchored in the PM, surrounds the MS and C rings; brown capsule-like
  • Fli proteins: motor switch; reverses the direction of the flagella in response to intracellular signals
• Archaeal Flagella

  • shorter than bacterial flagella
  • several different flagellin are known from archaea; but this does not bear any relationship with those of the bacterial flagellin
  • solid flagellum attached to the pseudomurein
  • less torque; slower
  • powered by ATP
• Eukaryal Flagella

  • bending movement
  • sliding filament system
  • powered by ATP
• Flagellar Synthesis

  1. MS and C rings assemble in the cytoplasmic membrane followed by P and then the L ring
  2. The hook and cap assemble next
  3. Flagellin proteins will flow through the hook to form the filament
  4. Cap proteins will guide the position of flagellum
• Gliding Mechanisms of Some Bacteria

  1. Cyanobacteria: secretes polysaccharide slime
  2. adheres to the surface and the cell is pulled along
  3. Myxobacterium: twitches — repeated extension and retraction of type IV pili
  4. propels
  5. Protein adhesion complex; cytoplasmic motility
  6. Flavobacterium johnsoniae: no slime or type IV pili
  7. outer membrane proteins (motility proteins) move in the opposite direction as the cell
  8. Ratcheting mechanism
• Gliding Motility

  • used on solid surface
  • slower and smoother form of movement
  • occurs in filamentous or rod-shaped bacteria
• Microbial Taxis


  Taxes: response to chemical or physical gradients in nature; movement is either directed or away from the agent

  1. Chemotaxis: response to chemicals; attractants or repellants
  2. Sensory response system
  3. The degree of methylation of MCPs (Methyl-accepting Chemotaxis Proteins) control the ability of the bacteria to respond to attractant and repellants, leading to adaptation
  4. CheR adds methyl groups to MCP; CheB-P removes methyl
  5. Phototaxis: response to light; light sensor instead of MCP
  6. Aerotaxis: oxygen
  7. Osmotaxis: high ionic strength
  8. known among swimming prokaryotes
  9. Hydrotaxis: water