Archaeal diversity

Question 1

Similarities between archaea and bacteria

Answer 1

Unicellular in most cases
Lack nucleus and membrane-bound organelles
Contain 70s ribosomes (50s and 30s subunits)

Question 2

Similarities between archaea and eukaryotes

Answer 2

DNA polymerases and RNA polymerase
RNAP in archaea is like RNAPII in eukaryotes

Question 3

Archaea unique in

Answer 3

None of the known species are pathogens of plants or animals
Cell envelope

Question 4

Archaea cell envelope

Answer 4

Glycerol phosphate head is attached to two isoprenoids – similar in length to fatty acid in bacteria
Each isoprenoid unit consists of 5 carbon atoms arranged in a specific pattern
In some the bilayer is replaced by a phospholipid monolayer = very long isoprenoid chains capped by glycerol phosphate heads at both ends
Isoprenoid bilayers and monolayers are more stable than bacterial phospholipid membranes at low pH, high temperatures and salt concentrations = helps archaea withstand harsher environments

Question 5

Cell of archaeal cells

Answer 5

1. Walled archaea
   Some have cell walls made of polysaccharides of a type of peptidoglycan = pseudomurein/pseudopeptidoglycan
   S-layers are composed of only one or sometimes two different glycoproteins
   Pseudo is made of N-acetylglucosamine + N-acetyltalosaminuric acid = both linked by beta 1-3 glycosylic bonds = lysozyme insensitive
2. Wall-less archaea
   Do not have cell walls
   Protect cell membrane with a S-layer consisting of proteins/glycoproteins interlocked forming a lattice

Question 6

Archaeal taxonomy

Answer 6

4 super-phyla – euryarchaeota, tack, dpann, asgard
Eukaryotes suggested to have emerged from asgard super-phylum

Question 7

Archaeal diversity

Answer 7

Able to grow in extreme environments but not restricted to – also abundant in soil, freshwater and marine habitats
i. Thermoacidophiles = grow at more than 70 degrees c and pH as low as 2
ii. Extreme halophiles = need high salt concs to grow otherwise they lyse, present in salt-evaporation ponds, produce carotenoid pigments which turn salt evaporation ponds bright red
Haloarchaea need to overcome the challenge that they are strict aerobes and oxygen has low solubility in high-salt environments
When o2 becomes limiting some have alternative to aerobic respiration
Bacteriorhodopsin is a membrane protein that acts as a light driven proton pump
1. absorption of photons by bacteriorhodopsin initiates the transport of protons out of the cell
2. resulting in a transmembrane proton gradient
3. ATP synthase can use the proton gradient to phosphorylate ADP and form ATP
iii. Methanogens use co2 for respiration reducing it to methane = unique to archaea
Present in animal rumens
Ruminants wouldn’t be able to obtain energy from grass without
Ruminants produce 10-20% of the methane in earths atmosphere
Make natural gas
Abundant in landfills
Methanogenesis takes places 1 year after solid waste is deposited
Methane captured and used as a fuel, avoids greenhouse emissions and reduces use of fossil fuels