Archaea

Question 1

Key Features of Archaea

Answer 1

No nucleus or membrane-enclosed organelles

30S Subunit, 16S rRNA

Circular membrane

Can survive at 70 degrees

Genes organised in operons, no introns

Question 2

The Archaeal Cytoplasmic Membrane

Answer 2

Lipid bilayer formed from glycerol diethers composed of C20 phytanyl lipids

or

Lipid monolayer formed from diglycerol tetraethers composed of C40 biphytanyl lipids

Both are extremely resistant to denaturing due to heat and are widespread among thermophiles

Question 3

Domain: Archaea

Answer 3

• Crenarchaeota – Many hyperthermophylic species

– Often chemolithotrophic (energy from oxidation of inorganic compounds)

– autotrophic (CO2 as sole carbon source)

• Euryarchaeota

– Physiologically diverse

– Many are extremeophiles

Question 4

Hyperthermophiles

Answer 4

Isolated from geothermal springs and soils – Temperatures of 100°C or more

• Sulphur rich springs (solfatarans) – pH ranges from mildly alkaline to pH 1 – Low pH (H2SO4 )
• Hydrothermal vents – Under sea hot spring – Water is under pressure – Temperatures above 100°C (up to 500°C)

Question 5

Order Sulfolobales

Answer 5

ex: Sulfolobus acidocaldarius – Grows in sulphur-rich acidic hot springs – Aerobic chemolithotrophs that oxidize reduced sulphur or iron – 90°C, pH 1-5 – Spherical/ lobed – Adheres to sulphur crystals

S layer: crystalline array of proteins - Anchored in the cytoplasmic membrane

Question 6

Order Desulfurococcales

Answer 6

ex: Pyrolobus fumarii – Optimum growth temperature 106°C – Lives in the walls of black smokers – S layer (cell wall) composed of protein – Membranes composed of glycerol tetraethers – Autotrophic – Facultative aerobe – Obligate H2 chemolithotroph – NO3 - is used as a terminal acceptor in strict anaerobic conditions NO3 - & H2 ->NH4

Question 7

Problem – Instability of biomolecules at high temperature

Answer 7

Proteins • Molecular Chaperones (heat shock proteins) – Proteins which refold partially denatured proteins – Thermosome – Produced in very high amounts at growth limiting temperatures

Lipids • glycerol tetraethers in membranes

DNA • Reverse DNA Gyrase – Introduces positive supercoils • DNA binding proteins – Sac7d in Sulfolobus, binds the minor groove, increases Tm by 40°C – Archeael histones, DNA wound and compacted

Question 8

Nonthermophilic Crenarchaeota

Answer 8

Found in nutrient poor marine environments • Can survive in very cold seawater and ice • Planktonic (floating) • Identified by SSU rRNA sampling • Can fix inorganic carbon – Probably play a key role in the carbon cycle

Question 9

Halophilic archaea

Answer 9

ex: Halobacterium salinarum – Extreme halophile – Have a requirement for high salt concentrations, typically at least 1.5 M (~9%) NaCl for growth – Found in sea salt evaporation ponds, salt lakes, and artificial saline habitats (i.e., salted foods)

Question 10

Adaptations to high salt

Answer 10

• Problems: – Osmotic forces – High solute levels inside cells
• Maintain positive water balance by pumping K+ in to cells – Higher K+ inside than Na+ outside cell
• Glycoprotein cell wall – Cell wall stabilised by Na+
• Cellular proteins composed of more acidic amino acids – More soluble at high solute concentration

Question 11

Methanogens

Answer 11

• Produce methane (CH4 ) – Several carbon substrates can be used – ATP is produced
• Unique to Archaea – Important in degradation of organic matter – Found in: Sediments low in O2 (Marsh, swamp etc) Animal digestive tracts Hydrothermal vents • Obligate anaerobes
• Methanobacterium – Pseudomurin in cell wall

Question 12

Another table comparing domains

Answer 12