Morphology

• Hook


  In bacterial flagellar structure, the hook acts as a flexible coupling between the basal body and the filament. It connects the motor embedded in the cell membrane (basal body) to the long, helical tail-like filament that extends from the cell. The hook allows for the transmission of torque generated by the motor to rotate the filament, propelling the bacterium forward.
• Flagellum (plural: flagella)


  A whip-like appendage extending from the surface of some bacterial cells. It is primarily involved in bacterial motility, allowing bacteria to move toward or away from particular stimuli such as nutrients or toxins. The flagellum is composed of a filament, hook, and basal body.
• Basal body


  A structure that anchors the flagellum to the bacterial cell membrane and cell wall. It is a complex molecular machine that spans the cell envelope and serves as the motor that drives flagellar rotation.
• Bacterial morphology


  • Monotrichous
  • Lophotrichous
  • Amphitrichous
  • Peritrichous
• Bacteria with different flagellar arrangements

  • Vibrio cholerae
  • Helicobacter pylori
  • Proteus mirabilis
  • Spirillum
• Donor Cell Formation


  1. Donor bacterial cell contains genetic material (often a plasmid)

  2. Donor cell synthesizes a pilus

  3. Pilus makes contact with recipient cell

  4. DNA transfer through channel between donor and recipient

  5. Transferred DNA integrates or exists as plasmid in recipient

  6. Recipient cell becomes a donor in subsequent conjugation events
• Capsule


  A well-organized and tightly bound layer of polysaccharides or polypeptides that surrounds the bacterial cell. Provides protection from desiccation, phagocytosis, and other environmental stresses. Facilitates adherence to surfaces and tissues, and can contribute to bacterial virulence.
• Slime Layer


  A loosely organized and unstructured layer of extracellular polysaccharides that surrounds the bacterial cell. Facilitates attachment to surfaces and biofilm formation.
• Outer Membrane


  Consists of a lipid bilayer with lipopolysaccharides (LPS) in the outer leaflet. Forms a selectively permeable barrier that protects the bacterial cell from various environmental stresses. LPS molecules contribute to structural stability and impermeability, while porins allow diffusion of small molecules.
• Cell Wall


  A rigid and protective structure that surrounds the cell membrane, providing structural support and shape to the bacterial cell. Plays a crucial role in maintaining cell integrity, resisting osmotic pressure, and protecting the cell from environmental stresses.
• Cell Wall Types


  • Gram-positive
  • Gram-negative
• Gram-Positive Cell Wall


  • Thick layer of peptidoglycan (up to 90% of cell wall dry weight)
  • May contain other components like teichoic acids and proteins
• Gram-Negative Cell Wall


  • Thinner layer of peptidoglycan (1-2 layers)
  • Peptidoglycan layer located in the periplasmic space
  • Outer membrane contains lipopolysaccharides (LPS)
• Periplasm


  The space between the inner and outer membranes in Gram-negative bacteria.
• Inner Membrane


  The inner membrane of the bacterial cell envelope.