Lec 7: Diversity of Archaea

Question 1

Extremophiles

Answer 1

Archaea considered microbes of extreme environments

Question 2

Grouping of Archaea

Answer 2

Based on 16s rRNA sequence analysis

3 phyla: crenarchaeota, euryarchaeota, thaumarchaeota

Question 3

General features of Archaea

Answer 3

1. Cell walls do not contain peptidoglycan (no muramic acid).
2. Membrane lipids differ from bacterial & eukaryotic lipids
3. External structures

Question 4

Cell wall of Archaea

Answer 4

Do not contain peptidoglycan

No muramic acid

Composed of pseudomurein or polysaccharide or protein (s-layer)

Question 5

Archaeal membrane lipids

Answer 5

Differ from bacterial and eukaryotic lipids

Have branched chain hydrocarbons connected to glycerol with ether links (bacteria & eukaryotes: non-branched ester bonds)

C20 diethers -> membrane bilayer

C40 tetraethers -> more rigid monolayer membrane. Typical of thermophiles (more heat stability)

Question 6

External structures

Answer 6

Pili

Cannulae: unique to Archaea (allow Archaea not to be easily washed away etc). Hollow, tube-like surface structures. Connect cells to form network

Hami: unique to Archaea. Tiny grappling hooks, each barbed fibre ends in 3-pronged tip. Maybe used to stick cells together

Question 7

Crenarchaeota

Answer 7

Thermophiles or hyperthermophiles

Many dependent on sulfur for energy metabolism

Many are strict anaerobes

Pyrodictium (has cannulae), pyrolobus (hyperthermophile), sulfolobus (thermoacidophile)

Question 8

Methanogens & methanotrophs

Answer 8

Euryarchaeota

Generate methane gas

Consume CO2 and H2

Question 9

Haloarchaea

Answer 9

Euryarchaeota

Extreme halophiles

Grow in high-salinity habitats (salt lakes)

Cope with osmotic stress by: increasing cytoplasmic osmolarity (accumulating small organic molecules like glycine), concentrate salt inside cell to levels equivalent to external environment

Red-yellow pigmentation

Cubes, pyramids

Question 10

Thermoplasms

Answer 10

Euryarchaeota

Thermoacidophiles that lack cell walls

Spherical

Membrane can change shape

Grow in refuse streams/piles of coal mines

Question 11

Extremely thermophilic S0 reducers

Answer 11

Euryarchaeota

Genus Pyrococcus

Rapidly motile coccus (multiple polar flagella)

Have industrial uses: into plants to increase heat tolerance, heat stable DNA polymerase in PCR

Question 12

Sulfate-reducing Euryarchaeota

Answer 12

Euryarchaeota

Genus Archaeoglobus

Thermophilic

In deep sea vents, oil deposits, hot springs

Reduce sulfate to sulfide (extracting e- from H2, lactate, glucose)

Question 13

Thaumarchaeota

Answer 13

Mesophilic aerobic ammonia oxidising

Widespread in oceans, soils, sediments

Oxidise ammonia to nitrite

Live in symbioses with bacteria