Domain Bacteria

Rucete ✏ Biology In a Nutshell

1. Characteristics of Bacteria

  • Prokaryotic cells: No nucleus or membrane-bound organelles
  • Cell walls contain peptidoglycan (unlike archaea)
  • DNA is not associated with histone proteins
  • Sensitive to antibiotics like streptomycin and chloramphenicol
  • Reproduce asexually by binary fission

2. Shapes of Bacteria

  • Cocci: spherical
  • Bacilli: rod-shaped
  • Spirilla: spiral-shaped

3. Movement

  • Some bacteria use flagella for movement
  • Others may glide or exhibit twitching motion

4. Types of Bacteria

a) Cyanobacteria (Blue-green algae)

  • Photosynthetic autotrophs that use chlorophyll a
  • Contain accessory pigments called phycobilins
  • Have heterocysts—specialized cells for nitrogen fixation

b) Chemosynthetic Bacteria

  • Autotrophs that obtain energy by oxidizing inorganic substances
  • Include nitrifying bacteria that convert ammonia (NH₃) to nitrites (NO₂⁻) and then to nitrates (NO₃⁻)

c) Nitrogen-Fixing Bacteria

  • Convert atmospheric nitrogen (N₂) into ammonia (NH₃)
  • Often live in mutualistic relationships with plants (e.g., root nodules of legumes)

d) Spirochetes

  • Spiral-shaped bacteria that move using a corkscrew motion
  • Some are free-living, others are pathogenic (e.g., Lyme disease)

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