All bacteria share features common to every prokaryotic cell:
- They lack a nucleus and membrane-bound organelles
- They have circular DNA that is naked (not bound to protein)
- They have smaller ribosomes (70S)
However different types of bacteria can be distinguished according to a number of characteristics:
- Shape – Round (coccus), rod-like (bacillus), comma-shaped (vibrio) or spiral (spirilla / spirochete)
- Cell wall composition – Gram-positive (thick peptidoglycan layer) or Gram-negative (lipopolysaccharide layer)
- Gaseous requirements – Anaerobic (obligate or facultative) or aerobic
- Nutritional patterns – Autotrophic (photosynthetic or chemosynthetic) or heterotrophic
Bacterial Sub-Classifications
