CHAPTER 4 - Archaea

Archaea classification

this kingdom (domain) consists of unicellular prokaryotes

• has no membrane bound organells

• likely as old as bacteria

  • 3.5-3.8 bya → speculated because hopanoids were found in sedimentary rock which implies that bacteria were present BYA (however not confirmed)

• contains many unusual organisms

what are mixobacteria?

these are bacteria that eat other bacteria

• consists of gram (-) rods that act together

  • aka hunt as a group

    • when food is scarce they produce spores by clumping together to reproduce and disperse themselves

      • likely to find more food

Differences between Archaea and Eubacteria

Differences are:

• Archaea

  • membrane lipids have a ether linkage

  • membrane contains isoprenoid based hydrocarbons in the lipids

• Bacteria (Eubacteria)

  • membrane lipids contain an ester linkage

  • membrane contains fatty acids in the lipids

Archaeal membrane integrity

Archaeal membranes contain covalent bonds in their membrane lipids

• additional to the isoprenoids and ether linkages present

  • ether linkages consist of an oxygen molecule bonded to carbon on either side

    • the covalent bonds make these lipids more thermally stable, making them withstand more exterme temperatures

    • The membrane layer is a monolayer

Bacterial membrane integrity

the membrane in bacteria contain double bonds

• additonal to the fatty acids and ester linkages

  • ester linkages are susceptible to low and high temps/pH

    • this makes them easy to break

      • they are also easily hydrolyzed

    • their membrane layer consists of a bi layer

Archaea and Bacterial membrane differences

Their differences are:

• Archaea

  • uses glycerol-1-phosphate in their membrane lipids

  • uses the enzyme glyverol-1-phosphate dehydrogenase

• Bacteria

  • uses glycerol-3-phosphate in their membrane lipids

  • usues the enzyme glycerol-3-phosphate dehydrogenase

• Indicates that they likely did not evolve from e/o

Archaeal ribosomal RNA

consists of a 16S small subunit and a 23S and 5S large subunit

• they also have a 5.8S large subunit, which is also seen in Eukaryotes

Archaeal Proteins

these are involved in DNA replication, transcription and are more similar to Eukaryotes than bacteria

Is there peptidoglycan in Archaeal cell walls?

No archaea cell walls do not possess peptidoglycan

• instead some Archaea contain pseudomurein in their cell walls

  • this is similar to peptidoglycan but uses a different sugar and L-amino acids

• Archaea have many different cell wall structures including protein S-layers

2 major phyla in Archaea

1. Crenarchaeota

2. Euryarchaeota

What are 2 other phyla's that aren't major and their characteristics?

1. Korarchaeota → only uncultured strains (cannot be cultured on petri plates)

2. Nanoarchaeota → very small! (Nanoacharaeum equitans may be the smallest prokaryote)

• also maye indicate the minimum size & function to be an organism

Crenarchaeota

in this phyla known strains are thermophilia (they really hot temperatures) or hyperthemophilic

• e.g. Thermoproteus grows between 70 - 90 degrees C (deeply branching group, perhaps the earliest from cellular life.)

• e.g pyrolobus grows up to 113 celsius

  • found underwater near underwater volcanoes

• Also consists of acidophiles (likes acidic environments)

  • e.g. Sulfolobus grows at pH 2

• Uncultivated representatives seem to be widespread

  • e.g. found in polar and temperate marine water, soil, sediments

Euryarchaeota

this phyla is very widespread and diverse

• consists of:

  • Methanogens

    • strict anaerobes (cannot survive or grow in oxygen)

    • They convert CO2 and H2 or C1 compounds (formate and methanol) into methane (CH4)

  • Exterme halophiles → likes high salt [ ] environments (5 Molar)

  • Thermophiles → likes hot temperatures

TACK superphylum

Includes serveral groups of Archaea that seem to be related and form a deep branch

• Includes Batharchaeota and Geoarchaeota

  • may include the ancestor of Eucaryotes

Heimdallarchaeota

consists of organisms that are similar to eukaryotes

Metagenomics

Where organisms are only known from DNA isolated from marine water, sequenced and assembled into genomes

→ takes 5 years to cultivate