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
•
- Lack cell walls, but have elaborate S-layer
•
- Reduce sulfur at higher temperatures
Desulforococcus mobilis
- Hot springs
Ignicoccus islandicus
- Marine organism
Figure 19.8
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
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
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: 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
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
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
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
Great Salt Lake
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
Figure 19.31
Retinal-Based Photoheterotrophy
• Animation: Light-Driven Ion Pumps and
Sensors
Click box to launch animation
Halophilic prokaryotes
Halobacterium selinarum
H. salinarum glycoprotein cell wall
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