achaea. figure 19.2 figure 19.5 crenarchaeota the name crenarchaeota means “scalloped archaea.”...
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CrenarchaeotaThe name Crenarchaeota means “scalloped
archaea.”
- Are often irregular in shape
All crenarchaeotes synthesize a distinctive tetraether lipid, called crenarchaeol.
Figure 19.6
Crenarchaeota• Desulfurococcales• - Lack cell walls, but have elaborate S-layer• - Reduce sulfur at higher temperatures
Figure 19.8
Desulforococcus mobilis
- Hot springs
Ignicoccus islandicus
- Marine organism
CrenarchaeotaBarophilic
hyperthermophiles
- Grow near hydrothermal vents on the ocean floor
- A common feature is the black smoker.
- Crenarchaeotes that are vent-adapted:
- Pyrodictium abyssi
- Pyrodictium occultum
Figure 19.9
CrenarchaeotaSulfolobales
- Include species that respire by oxidizing sulfur (instead of reducing it)
- Found within hot springs
Figure 19.13
- Sulfolobus solfataricus
- A “double extremophile”
- Grows at 80oC and pH 3
- Oxidizes H2S to sulfuric acid
Crenarchaeota• 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.
Figure 19.17
Euryarchaeota: MethanogensEuryarchaeota 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
- Landfills
- Digestive tracts of animals
- Termites
- Cattle
- Humans
- Marine benthic sediments
Anaerobic Habitats for Methanogens
Figure 19.22A
Figure 19.22B
Biochemical pathways of methanogens involve unique cofactors.
- These transfer the hydrogens and increasingly reduced carbon to each enzyme in the pathway.
Biochemistry of Methanogenesis
Figure 19.25
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.
Biochemistry of Methanogenesis
Figure 19.26
Euryarchaeota: HalophilesMain 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. Figure 19.29B
Figure 19.28
• Animation: Light-Driven Ion Pumps and Sensors
Click box to launch animation
Retinal-Based Photoheterotrophy
Nanoarchaeota
- Is an obligate symbiont of the crenarchaeote Ignicoccus hospitalis
- Host and symbiont genomes have been sequenced, revealing extensive coevolution.
Figure 19.36
Nanoarchaeum equitans
The smallest known euryarchaeotes.