Diversity of Archaea

• Archaea

  The word "archaea" comes from the Ancient Greek word archaios, which means "ancient" or "primitive"
• Archaea

  • Many features in common in Eukarya (genes encoding protein: replication, transcription, translation)
  • Features in common with Bacteria (genes for metabolism, initially grouped with Bacteria as Archaebacteria)
  • Unique rRNA gene structure
  • Capable of methanogenesis
• Archaea are highly diverse with respect to morphology, physiology, reproduction, and ecology
• Archaea are best known for growth in anaerobic (absence of oxygen), hypersaline (high salt concentration), pH extremes (very acidic or basic), and high-temperature habitats
• Archaea are also found in marine arctic (low) temperature and tropical waters
• Peptidoglycan structure


  Archaea do not possess a peptidoglycan structure
• Membrane layer


  Archaea possess a membrane layer
• Membrane-bound organelles


  Archaea do not possess membrane-bound organelles
• Flagella-like structures


  Archaea possess flagella-like structures
• Bacteria and Archaea do not form a monophyletic phylogeny
• Archaea and Eukarya form a monophyletic group
• This proves that Archaea are more closely related to Eukarya than to Bacteria, phylogenetically
• Archaeal size and shape

  • Much like bacteria, cocci, and rods are common shapes
  • Other shapes can also exist (no spirochetes or mycelial forms yet, branched/ flat shapes)
  • Sizes vary (typically 1-2 x 1-5 µm for rods, 1-5 µm in diameter for cocci)
  • Smallest observed is 0.2 µm in diameter
• S layer


  A proteinaceous layer that covers the entire outermost surface of the archaeal cell
• S layer functions


  • Protect from ion and pH fluctuations, osmotic stress, enzymes, and predation - For extreme conditions
  • Maintain shape and rigidity
  • Promotes adhesion to surfaces
  • Protects from host defenses - For bacteria
  • Potential use in nanotechnology
  • Protection against bacteriophages, Bdellovibrios, and phagocytosis
  • Resistance against low pH
  • Barrier against high-molecular-weight substances (e.g., lytic enzymes)
  • Stabilization of the membrane (e.g. in Deinococcus radiodurans - Resistance to radiation)
  • Resistance against electromagnetic stress (e.g. ionizing radiations and high temperatures)
  • Provision of adhesion sites for exoproteins
• Archaeal membranes


  • Composed of unique lipids with isoprene units (five carbon, branched) and ether linkages rather than ester linkages to glycerol
  • Some have a monolayer structure instead of a bilayer structure
• Archaeal cell envelopes


  • Varied S layers attached to plasma membrane
  • Pseudomurein (peptidoglycan-like polymer)
  • Complex polysaccharides, proteins, or glycoproteins found in some other species
  • Only Iginococcus has outer membrane
• Pseudomurein


  A peptidoglycan-like polymer found in archaeal cell walls
• Archaeal cell nutrient uptake

  • Use many of the same mechanisms as bacteria: Facilitated diffusion, Active transport (primary and secondary)
  • No group translocation mechanisms have yet been discovered in archaea
• Ribosomes


  • Complex structures, sites of protein synthesis
  • Bacterial/archaeal ribosome = 70S (50S large subunit and 30S small subunit)
  • Eukaryotic ribosome = 80S (60S and 40S)
• Nucleoid


  Irregularly shaped region in bacteria and archaea, usually not membrane bound, location of chromosome and associated proteins, usually 1 (some evidence for polyploidy in some archaeons)
• Pili


  Not well understood, some composed of pilin protein and homologous to bacterial type IV pili proteins, pili formed have a central lumen similar to bacterial flagella, but not bacterial pili, may be involved in archaeal adhesion and conjugation mechanisms
• Cannulae


  Hollow, tubelike structures on the surface of thermophilic archae in the genus Pyrodictium, function is unknown, may be involved in formation of networks of multiple daughter cells, unique to archaea, discovered in marine organisms
• Hami


  'Grappling hook' appearance (branched), involvement in cell adhesion mechanisms, not well understood
• Extremophiles


  Organisms that thrive under "extreme conditions" such as alkaline, acidic, extremely cold, or extremely hot environments
• Types of extremophiles


  • Acidophile (low pH, optimally 3 or below)
  • Alkaliphile (high pH, optimally 9 or above)
  • Anaerobe (little to no oxygen needed for growth)
  • Halophile (high salt, at least 0.2M, needed for growth)
  • Psychrophile (very low heat, temperatures of less than -15 C)
  • Moderately thermophile (survive, grow, and multiply at 45 C)
  • Extreme thermophile (survive between 45-80 C)
  • (Hyper)thermophile (high heat, 80-122 C)
  • Metallotolerant (tolerating high levels of metal concentrations)
  • Oligotroph (can grow in nutritionally limited environments)
  • Osmophile (can grow in high sugar concentrations)
  • Radioresistant (extreme radioactivity)
  • Xerophile (grow in very dry conditions)