General Biology/Classification of Living Things/Prokaryotes

For Eubacteria, please visit General Biology/Classification of Living Things/Eubacteria.


  • Proposed as separate group from (eu)bacteria by Carl Woese
    • based on structure and metabolic pathways
    • inhabit extreme environments
    • unique branched lipids in membrane
  • Share traits with both eukaryotes and eubacteria, e.g., RNA polymerase, introns
  • Biochemically diverse
  • Economically important
    • Taq polymerase used in PCR


  • Methanogens
  • Halophiles
  • Thermophiles

Underground bacteriaEdit

  • Metabolism
    • built around inorganic energy sources
  • e.g., basalt reacts with H2O to release hydrogen which is catalytically combined with CO2 to form carbohydrate (akin to photosynthesis)
  • may result in deposit of minerals
  • Unresolved problems
    • Did bacteria move downward from surface or did they first evolve there, protected from harsh surface conditions?
    • Could bacteria be ejected into space in rocks?

Prokaryote evolutionEdit

  • Tentative, subject to change
  • Derived largely from molecular systematics (rRNA sequences)
  • Note: most bacteria can’t be cultured, thus hard to study! (Studied by PCR of water/soil samples)

Domains of life: characteristicsEdit

This text is based on notes very generously donated by Paul Doerder, Ph.D., of the Cleveland State University.