General Biology/Classification of Living Things/Prokaryotes

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

Archaea

• 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

Types

• Methanogens
• Halophiles
• Thermophiles

Underground bacteria

• 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 evolution

• 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: characteristics

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