BIOS 312 Archaea

T/F: Ongoing research has shown more genomic similarity between Archaea and Bacteria, rather than Archaea and Eukarya

False, more similarity between Archaea and Eukarya

T/F: We now believe that a member of the “Asgard Superphylum” of Archaea may be a pre-eukaryotic cell

True

Asgard Archaeons

• Anaerobic, amino acid-oxidizing archeaon that grows syntrophically with hydrogen and formate-utilizing microorganisms

• Small, coccus that produces chains of blebs and membrane-based protrusions

• Isolated from deep-sea methane sediment off the Kumano area in Japan

• Candidatus Prometharcheum syntrophicum

• The isolation of this organism led to a new model for the origin of Eukaryotic life

  • We now think an ancient archaeon engulfed a neighboring bacterium that was capable of using toxic oxygen to make ATP

The Entangle-Engulf-Endogenize (E³) Model

An Asgard archaeon ("Entangle") uses long, tentacle-like protrusions to trap a bacterial partner (syntrophy), eventually engulfing it ("Engulf") and developing an endosymbiotic relationship where the host and bacterium share resources, leading to the bacterium becoming a mitochondrion ("Endogenize").

What are the major groups of Archaea?

Groups are based on a comparison of ribosomal proteins from sequenced genomes (share many characteristics with Bacteria and Eukarya)

1. Euryarchaeota

2. Crenarchaeota

3. Thaumarchaeota

4. Korarchaeota

5. Nanoarchaeota

Euryarchaeota

• Large, physiologically diverse phylum

1. Haloarchaea

   1. Key genera: Halobacterium, Haloferax, Natronbacteria

   2. Extremely halophilic (high salt, at least 1.5M NaCl)

   3. Reproduce by binary fission, no resting stage or spores

   4. Nonmotile, obligate aerobes

   5. Possess adaptations to life in highly ionic environments

   6. Some can even use light to synthesize ATP

Halophiles need to maintain ____ balance

Osmotic

• Usually achieved by accumulation or synthesis of compatible solutes

• Halobacterium species instead pump large amounts of K+ into the cell from the environment

  • Intracellular K+ concentration exceeds extracellular Na+ concentration and positive water balance is maintained

Light-driven ATP production

• Proteins in archaea are highly acidic and contain fewer hydrophobic amino acids and lysine residues

• Some haloarchaea are capable of light-driven synthesis of ATP

  • Bacteriorhodopsin: cytoplasmic membrane proteins that can absorb light energy and pump protons across the membrane

    • Used when aeration is low

    • Haloarchaea use this to supplement their metabolism

• Other rhodopsins can be present

  • Halorhodopsin: light driven pump that pumps Cl- into cell as an anion for K+

  • Sensory rhodopsins: control phototaxis

Methanogens

• With the exception of methanogenesis, bioenergetics and intermediary metabolism of Archaea are similar to those found in bacteria

• Autotrophy via several different pathways is widespread in Archaea

• Key genera: Methanobacterium, Methanocaldococcus, Methanosarcina

  • Microbes that produce CH₄

  • Found in many diverse environments

  • Taxonomy based on phenotypic and phylogenetic features

• Process of methanogenesis first demonstrated over 200 years ago

• Demonstrate diversity of cell wall chemistries

  • Pseduomurein (Methanobacterium)

  • Methanochondrotin (Methanosarcina)

  • Protein or glycoprotein (Mthanocaldococcus)

  • S-layers (Methanospirillum)

• Methane is over 20 times more effective in trapping heat in the atmosphere than CO2 over a 100 year period

Thermoplasmatales

• Taxonomic order within the Euryarchaeota

• Contains 3 genera

  • Thermoplasma, Ferroplasma, Picrophilus

• Thermophilic and/or extremely acidophillic

• Thermoplasma and Ferroplasma lack cell walls

Thermoplasma

• Chemoorganotrophs

• Facultative aerobes via sulfur respiration

• Thermophilic and acidophilic

• Evolved unique cytoplasmic membrane structure to maintain positive osmotic pressure and tolerate high temperatures and low pHs

  • Membrane contains lipopolysaccharide-like material (lipoglycan) consisting of tetraether lipid monolayer membrane with mannose and glucose

  • Membrane contains glycoproteins but not sterols

Ferroplasma

• Chemolithotrophic and acidophillic

• Oxidizes Fe²⁺ to Fe³⁺, generating acid

• Grows in mine tailings containing pyrite (FeS)

Nanoarchaeum

Nanarchaeum equitans

• One of the smallest cellular organisms (0.4 um)

• Obligate symbiont of the Crenarchaeote Ignicoccus

• Contains one of the smallest genomes known

• Lacks genes for all but core molecular processes

• Depends upon host for most of its cellular needs