Achaea

Figure 19.2

Figure 19.5

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

Great Salt Lake

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

Figure 19.31

• Animation: Light-Driven Ion Pumps and Sensors

Click box to launch animation

Retinal-Based Photoheterotrophy

Halophilic prokaryotes

Halobacterium selinarum

H. salinarum glycoprotein cell wall

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.