Microbial Diversity (Part 2)

Question 1

Diversity of Archaea

Answer 1

• Phylogenetically Archaea are split into five phyla
• Breadth of phylogenetic diversity is similar to that of the Bacteria and Eukarya

Question 2

Euryarchaeota: Extreme Halophiles (Haloarchaea)

Answer 2

• Also known as halobacteria
• Example: Halobacterium salinarum
• Absolute requirement for high salt concentrations
  
  • Typically need at least 1.5 M (~9%) NaCl for growth
• Found in solar salt evaporation ponds and salt lakes where the salt concentration approaches saturation
  
  • Ex) Great Salt Lake (Utah), Dead Sea
  • Ex) soda lakes (highly alkaline hypersaline lakes)

Question 3

Euryarchaeota: Extreme Halophiles

Answer 3

• Adaptations for highly ionic environments
  
  • Halophiles need to maintain osmotic balance
    
    • Usually achieved by accumulation or synthesis of compatible solutes
  • Halobacterium salinarum pumps large amounts of K+ into the cell from the environment
    
    • Intracellular K+ concentration exceeds extracellular Na+ concentration
    • Water flows into the cell in hypersaline environments

Question 4

Euryarchaeota: Extreme Halophiles (Part 2)

Answer 4

• Some haloarchaea have a unique system for generating energy:
  
  • Light-driven synthesis of ATP without the use of
    chlorophylls
  • Instead they use a pigment called bacteriorhodopsin
• Bacteriorhodopsin
  
  • Integral membrane protein
  • Absorbs light energy and pumps protons across the membrane to make a PMF
  • PMF is used to generate ATP
  • They do not fix CO2
    
    • Ex) Photoheterotrophy

Question 5

Euryarchaeota: Methanogenic Archaea

Answer 5

• Only microbes capable of significant methane production: Methanogens
  
  • Ex) Methanobacterium
    4H2 + CO2 CH4 + 2 H2O
  • Produce the bulk of CH4 in the atmosphere
    
    • Important green house gas
  • Strict anaerobes, found in many diverse anaerobic environments
    
    • Ex) Cow’s gut; Sewage sludge

Question 6

Euryarchaeota: Methanogenic Archaea (Part 2)

Answer 6

• Demonstrate diversity of cell wall chemistries
• Pseudomurein used in Methanobacterium
  
  • Similar in structure to peptidoglycan
  • Less similar in composition to peptidoglycan
  • Only the Methanobacteriales family has this type of cell wall
    
    • Most other types of methanogens have a S-layer made of protein or glycoprotein as their cell wall

Question 7

Thaumarchaeota

Answer 7

• Accomplishes nitrification
• Ex) Nitrosopumilus maritimus
  
  • Aerobic, ammonia oxidizing chemolithoautotroph:
    
    • Converts NH3 into NO2- for energy
    • Uses CO2 for carbon
    • Abundant in open ocean water where they seem to be a major player in
      nitrogen cycling

Question 8

Nanoarchaeota

Answer 8

• Ex) Nanoarchaeum equitans
  
  • One of the smallest cellular organisms (~0.4 μm)
  • Obligate parasite 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

Question 9

Korarchaeota

Answer 9

• Ex: Korarchaeum cryptofilum
  
  • Obligately anaerobic chemoorganotroph
  • Hyperthermophile
  • Cells are long, thin filaments
  • Lacks many core genes
  • Depends on other members of hot springs community and cannot yet be grown in pure culture

Question 10

Crenarchaeota

Answer 10

• Most are hyperthermophiles
  
  • Found in extremely hot environments:
    
    • Boiling hot springs, deep ocean vents
  • Other representatives are found in extremely cold environments
• Chemoorganotrophs or
  chemolithotrophs
  
  • Most use sulfur in their metabolism

Question 11

Crenarchaeota (Part 2)

Answer 11

• Ex: Sulfolobus acidocaldarius
  
  • Grows in sulfur-rich acidic hot springs (~90°C, pH 2)
    
    • Hyperthermophile and acidophile
  • Aerobic chemolithotroph that oxidizes reduced sulfur or iron
  • Example:
    2S0 + 3O2 + 2H2O -> 2 H2SO4.

Question 12

Asgard Superphylum of Archaea

Answer 12

• Only known from sequence analyses from metagenomes. Ecological
  functions unknown (2012-13 published)
  
  • Metabolism inferred from sequencing-samples have been genome
    reconstructed
• This group is broken down into Phyla named after the Norse gods: Lokiarchaeota, Odinarchaeota, Thorarchaeota etc.

Question 13

Asgard Superphylum of Archaea (Part 2)

Answer 13

• On the basis of sequence similarity may represent the “missing link” between Archaea and Eukarya
• Members of this superphylum contain versions of genes previously thought to have been eukaryote-specific

Question 14

Facts

Answer 14

• 10 years to isolate and grow
• Will only grow in the presence of another bacteria Halodesulfovibrio (syntrophic growth)
• Anaerobic, slow growing