Achaea. Figure 19.2. Figure 19.5. Crenarchaeota. The name Crenarchaeota means “scalloped archaea.” - Are often irregular in shape All crenarchaeotes synthesize a distinctive tetraether lipid, called crenarchaeol . Figure 19.6. Crenarchaeota. Desulfurococcales
The name Crenarchaeota means “scalloped archaea.”
- Are often irregular in shape
All crenarchaeotes synthesize a distinctive tetraether lipid, called crenarchaeol.
- Lack cell walls, but have elaborate S-layer
- Reduce sulfur at higher temperatures
- Hot springs
- Marine organism
- Grow near hydrothermal vents on the ocean floor
- A common feature is the black smoker.
- Crenarchaeotes that are vent-adapted:
- Pyrodictium abyssi
- Pyrodictium occultum
- Include species that respire by oxidizing sulfur (instead of reducing it)
- Found within hotsprings
- Sulfolobus solfataricus
- A “double extremophile”
- Grows at 80oC and pH 3
- Oxidizes H2S to sulfuric acid
The crenarchaeote Cenarchaeum symbiosum inhabits the sponge Axinella mexicana.
- The relationship is unclear, but they can be co-cultured in an aquarium for many years.
Euryarchaeota means “broad-ranging archaea.”
Are dominated by methanogens
- All are poisoned by molecular oxygen and therefore require complete anaerobiosis.
- Major substrates and reactions include:
Carbon dioxide: CO2 + 4H2→ CH4 + 2H2O
Acetic acid: CH3COOH → CH4 + CO2
Methanol: 4CH3OH → 3CH4 + CO2 + 2H2O
Methylamine: 4CH3NH2 + 2H2O →
3CH4 + CO2 + 4NH3
Methanogens grow in:
- Anaerobic soil of wetlands
- Especially rice paddies
- Digestive tracts of animals
- Marine benthic sediments
Biochemical pathways of methanogens involve unique cofactors.
- These transfer the hydrogens and increasingly reduced carbon to each enzyme in the pathway.
The process fixes CO2 onto the cofactor methanofuran (MFR).
- The carbon is then passed stepwise from one cofactor to the next, each time losing an oxygen to form water, or gaining a hydrogen carried by another cofactor.
Main inhabitants of high-salt environments are members of the class Haloarchaea.
- Their photopigments color salterns, which are used for salt production.
- Most are colored red by bacterioruberin, which protects them from light.
Halophilic archaea require at least 1.5M NaCl.
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The smallest known euryarchaeotes.
- Is an obligate symbiont of the crenarchaeote Ignicoccus hospitalis
- Host and symbiont genomes have been sequenced, revealing extensive coevolution.