MC1: The archaea Flashcards
In what type of conditions do archaea usually live?
Extreme conditions
What are the three domains of life?
Bacteria, eukarya, archaea
Who, in 1977, announced the discovery of archaea?
Carl Woese
What did Carl Woese compare to discover the archaea?
Ribosomal RNA genes
What was Carl Woese doing when he discovered archaea?
He was looking at how different bacteria were genetically releated
Why are microbes harder to classify?
There is no fossil record of them
Why did Carl Woese look at the 16S rRNA gene?
- Conserved
- Present in all organisms
- Not subject to horizontal gene transfer
- 16S rRNA is part of the small subunit of the bacterial ribosome (it stabilises it)
- The loops vary by species
What were initially thought to be the three groups of archaea?
- Methanogens
- Halophiles
- Hyperthermophiles
Why were archaea initially viewed as exremophiles?
Because they had only been found living in harsh conditions such as hot springs and salt lakes
Why is the view of archaea as extremophiles no longer valid?
They have since been found living in many habitats, including soils, oceans, marshlands, and the human colon, oral cavity, and skin
Give examples of harsh conditions archaea can cope with. What are the names of organisms that can live in these conditions?
-
High salt concentrations
Halophiles live in hypersaline environments such as salt lakes -
Temperature
Thermophiles live in hot springs where archaea grow optimally at >80°C; some can reproduce at 122°C -
Acidic or alkaline conditions
Acidophiles can grow at pH 0 (equivalent to thriving in 1.2M H2SO4)
Alkaliphiles can grow at pH 11
What is the role of uncultured archaea in deep-sea marine sediements?
Removal of methane via anaerobic oxidation of methane stored in these sediments
What happens to methane at cold temperatures and high ocean pressure? What happens as oceans warm?
Methane combines with water into methane hydrate crystals
As oceans warm, this bubbles up, releasing more methane into the atmosphere
How do archaea generate terrestrial methane?
They are present in rice paddies and in the guts of cattle
They generate approx. 10-25% of global methane emissions
Are there any examples of archaeal pathogen or parasites?
No, but they are often mutualists or commensals
What proportion of humans have methanogens in their guts? What ability does this give them?
50% – they can set fire to their farts!
How are archaea exploited by humans?
- Methanogens are used in biogas production and sewage treatments
- Enzymes from thermophile archaea are exploited in biotechnology
How are archaeal products used by humans?
-
Pfu DNA polymerase from Pyrococcus furiosus allowed PCR to be used for DNA cloning which revolutionised molecular biology
- It has superior thermostability and proofreading abilities to Taq DNA polymerase – Pfu possesses 3’→5’ proofreading abilities so errors in Pfu DNA polymerase-generated PCR fragments will have fewer errors than Taq-generated PCR ones
- Amylases and galactosidases that function at over 100°C allow food processing at high temperatures, e.g. the production of low lactose milk and whey
- Their stability makes their enzymes easier to use in structural biology so they are used as a proxy for protiens of interest
What important role can archaea play in human disease treatment?
Archaeocins (a new class of antibiotics) differ in structure from bacterial antiiotics so may have novel forms of action
A few have been characterised but many more are believed to exist, especially within Holoarchaea and Sulfolobus
They may allow the creation of new selectable markers for use in archaeal molecular biology
Do archaea have peptioglycan cell walls?
No
What are the key differences between the cell walls of bacteria and archaea?
Arhcaeal cell walls are more chemically and structurally diverse
They are a semi-rigid lattice of pseudomurein, sugars, protiens, or glycoproteins
They do not contain peptidoglycan
Compare bacterial flagella to archaeal flagella.
Bacterial: helical filaments that rotate to provie motility
Archaeal: similar but different in many ways and non-homologous
Bacterial: produced by the addition of flagellin subunits at the tip
Archaeal: produced by the addition of flagellin subunits at the base
Bacterial: thicker and hollow allowing flagellin subunits to pass through
How are archaeal membranes different to bacterial and eukaryotic membranes?
-
Fatty acids
B/E: fatty acids linked by ester bonds to a glycerol
A: fatty acids linked by ether bonds to a glycerol -
Side chains
B/E: fatty acids
A: branced isoprenes -
Glycerol
B/E: D-glycerol
A: L-glycerol
How does RNA polymerase differ between bacteria and archaea/eukaryotes?
Bacteria have simple RNAP consiting of four polypeptides
Archaea have multiple RNAPs and more than eight polypeptides
Eukaryotes have multiple RNAPs and 10-12 polypeptides, closer in size to archaea
