1. Achaea

3. Figure 19.2 3

6. Figure 19.5 6

7. Crenarchaeota The name Crenarchaeota means “scalloped archaea.”
- Are often irregular in shape
All crenarchaeotes synthesize a distinctive tetraether lipid, called crenarchaeol.
Figure 19.6 7

8. Crenarchaeota Desulfurococcales
- Lack cell walls, but have elaborate S-layer
- Reduce sulfur at higher temperatures
Desulforococcus mobilis
- Hot springs
Ignicoccus islandicus
- Marine organism
Figure 19.8 8

9. Crenarchaeota Barophilic 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 9

10. Crenarchaeota Sulfolobales
- Include species that respire by oxidizing sulfur (instead of reducing it)
- Found within hot springs
- Sulfolobus solfataricus
- A “double extremophile”
- Grows at 80oC and pH 3
- Oxidizes H2S to sulfuric acid
Figure 19.13 10

11. 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 11

12. Euryarchaeota: Methanogens
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 12

13. Anaerobic Habitats for Methanogens
Methanogens grow in:
- Anaerobic soil of wetlands
- Especially rice paddies
- Landfills
- Digestive tracts of animals
- Termites
- Cattle
- Humans
- Marine benthic sediments
Figure 19.22A
Figure 19.22B 13

14. Biochemistry of Methanogenesis
Biochemical pathways of methanogens involve unique cofactors.
- These transfer the hydrogens and increasingly reduced carbon to each enzyme in the pathway.
Figure 19.25 14

15. Biochemistry of Methanogenesis
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.
Figure 19.26 15

16. Great Salt Lake

17. Euryarchaeota: Halophiles
Main inhabitants of high-salt environments are members of the class Haloarchaea.
Figure 19.28
- 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 17

18. Figure 19.31 18

19. Click box to launch animation
Retinal-Based Photoheterotrophy
Animation: Light-Driven Ion Pumps and Sensors
Click box to launch animation

20. Halophilic prokaryotes

21. Halobacterium selinarum

22. H. salinarum glycoprotein cell wall

24. Nanoarchaeota The smallest known euryarchaeotes. Nanoarchaeum equitans
- Is an obligate symbiont of the crenarchaeote Ignicoccus hospitalis
- Host and symbiont genomes have been sequenced, revealing extensive coevolution.
Figure 19.36 24