Dr Clokie - Archaea Flashcards
Describe archaea cell wall
- Pseudopeptidoglycan
- Basic components are N-acetylglucosamine and N-acetyltalosaminuronic acid, which are linked by β-1,3-glycosidic bonds
Differences in archaea cell wall and bacterial cell wall
- Bacterial peptidoglycan has N-acetylmuramic acid instead of N-acetyltalosaminuronic acid
- β-1,4-glycosidic bonds (not 1,3)
- Lysozyme cannot break the archaea’s 1,4 bond to degrade it, making it useless
Why is a lipid membrane important to cells?
- Prokaryotes expend energy to maintain a chemiosmotic potential - drives basic cellular processes
- Membrane is a barrier for this potential - futile ion cycling, ions moving across membranes is a source of energy loss
- Organisms require membrane fidelity to avoid futile ion cycling
In what 4 ways are archaeal lipids unique?
- Ether-linked lipids (not ester-linked)
- Side-chains are not fatty acids, but branched isoprenes
- Different chiral form of glycerol
- Some archaea possess lipid monolayers
What type of bacteria do archaea most resemble?
Gram-positive bacteria
Compare the structure of archaea lipids?
Archea:
1) Branched isoprene chains
2) Ether-linked lipids
3) L-glycerol
4) Phosphate
Bacteria & Eukaryotes:
1) Unbranched fatty acids
2) Ester-linked lipids
3) D-glycerol
4) Phosphate
What is the significance of the ether rather than ester bonds?
- Ether bonds are chemically more resistant than ester bonds.
- This stability might help archaea to survive extreme temperatures and very acidic or alkaline environments
What is a unique ability of the phospholipid bilayer in some archaea? Give an example
- The lipid bilayer is replaced by a monolayer.
- Essentially the tails of two independent phospholipid molecules fuse into a single molecule with two polar heads
- Fusion may make their membranes more rigid and better able to resist harsh environments
- Eg. Ferroplasma - highly acid conditions
Compare archaeal and bacterial flagella
- Bacterial flagella are helical filaments that rotate providing motility
- Archaeal flagella are superficially similar to bacterial flagella, but are different in many ways and considered non-homologous (convergent evolution)
- Bacterial flagella are produced by the addition of flagellin subunits at the tip; archaeal flagella grow by the addition to the base
- Bacterial flagella are thicker and hollow allowing flagellin subunits to pass through
- No sequence similarity being detected between the genes of the two systems
What features does archaea have in common with bacteria?
- No membrane defined nucleus
- Can have plasmids
- Not multicellular
- Genes organised as operons
What features does archaea have in common with eukarya?
- No sensitivity to streptomycin, chloramphenicol, rifampicin - Sensitivity to diphtheria toxin - Presence of histones - Complex DNA & RNA polymerase
What features are unique to archaea?
- No ester-linked lipids
- No peptidoglycan cell wall
- No pathogens
Name 5 viruses unique to the crenarchaeal group
- Fuselloviridae
- Rudiviridae
- Lipothrixviridae
- Ampullaviridae
- Salterprovirus
Describe Fuselloviridae
- ‘Lemon’ shaped
- Typically infect Sulfolobus sp. that inhabit volcanic springs (70-80°C, pH 2-3)
- SSV1, SSV2, SSV RH and SSV K1
- SSV1: Integrates into host genome via integrase protein (site specific)
- D-63: Dimeric homologues in SSV2 & SSVK1
- F-93: Dimeric homologues in SSV2 & SSVK1
Describe Rudviridae
- Double stranded linear DNA
- SIRV1 and SIRV2
- Typically infect Sulfolobus sp. that inhabit volcanic springs (70-80°C, pH 2-3)
- Very host specific
- SIRV1: no integration into host genome
Describe Lipothrixviridae
- Double stranded DNA
- SIFV, AFV, DAFS, TTV1, TTV2 and TTV3
- Typically infect Sulfolobus, Acidianus and Thermoproteus spp. that inhabit volcanic springs (70-80°C, pH 2-3)
- SIFV: Thick lipid envelope, virus core surrounded by lipid bilayer, no integration into host genome
Describe Ampullaviridae
- Double stranded DNA
- 5 different morphotypes ABVS
- Only known to infect Acidianus convivator that inhabit Pozzuai Italy hot springs (87-93°C, pH 1.5)
- Host specific
- ABVS: shape of virus thought to aid transfer of DNA - bottle neck/stopped host cell
receptors
Describe Salterprovirus
- Double stranded linear DNA
- HIS1 and HIS2
- Only known to infect Haloaracula hispanica which inhabit Pink Lakes Victoria Australia (20-50°C, pH 2-9)
- Host specific
- HIS1: heavily elongated versions observed
- HIS2: No short tail or elongated forms as seen in HIS1
Generally speaking, what group are usually:
1) Hyperthermophiles
2) Acidophiles
3) Methanogens
4) Halophiles
5) Ammonia oxidisers
1) Crenarchaea
2) Both Crenarchaea and Euryarchaeota
3) Euryarchaeota
4) Euryarchaeota
5) Thaumarchaeota
Name 3 hyperthermophiles
Thermococcus, Thermoproteus and Pryrodictium
Describe Thermoproteus and Pryrodictium
- Sulphur-dependent
- They are H2S autotrophs
- > 95°C
Describe Thermococcus
- Gram -ve coccoids with flagella
- They are organotrophic anaerobes
- > 70°C.
- Need S as an e- acceptor and make H2S + CO2
- Thermococcus coalescens can fuse
Name 5 electron acceptors and their products when H2 is the electron donor
- CO2 - Methane
- Fe(OH)3 - Magnetite
- Pyrite; SO4(2-) - Hydrogen sulphide
- NO3(-) - Nitrogen (NH3)
- O2 (traces) - Water
What is the electron acceptor and product when pyrite is the electron donor?
- O2
- H2SO4 (+FeSO4)
