Archaea methanogens

Archaea

Gram Staining Archaea(Not for the same reasons as Bacteria.)

* Gram+ cell wall like with Gram+ Bacteria, but different biochemical composition that peptidoglycan.

* Gram– due to glycoprotein surface layer not an outer membrane.

* Some with NO cell wall!

+ -

Pseudomurein(Murein = NAG-NAM of peptidoglycan in Bacteria)

* Insensitive to penicillin.* NAM replaced by NAT* Unique side-chain peptide cross-links.

Lipid Differences:

* Hydrocarbons not fatty acids

* Ether linked to glycerol not ester linked

Two leaves (bilayer) of C20 diethers

Single layer of rigid C40 tetraethers

Which is most likely that for an extreme thermophile?

Unique Means of

Autotrophy* No Calvin Cycle

* Reversed Modified TCA Cycle

* Reductive Acetyl-CoA

Methanogens

MethanogensObligate anaerobes dependent on fermentation bacteria.

Chemoheterotrophic: AcetoclasticAcetate to CO2 and methane

Chemoautotrophic: H2 or formate as energy & electron sourceCO2 to methane and other cellular

components

Methanogenesis Pathway

MCR protein is a 3 component complex; Component C is made of 3 polypeptide subunits (α,β,γ) encoded on mcrA, mcrB, and mcrG genes.

Methanogen Habitats

Aerobic respiration yields greatest energy due to very positive O2 redox potential.

Without O2, anaerobic respiration uses alternate terminal electron acceptors in the order of decreasing redox potential.

E = -240 mV

Methanogenesis

E = +820 mV

E = +420 mV

E = -200 mV

Anearobic Complex Organic

Matter Degradation

1) Hydrolysis

2) Fermentation

3) Acetogenesis

4) Sulfate Reduction

5) Methanogenesis

Carbon Cycle

Methylotrophy

Methane Production - Consumption

Subsurface Methane Production:

Methanogens (shallower)(12C reacts faster than 13C)

Geothermal (deeper)

Sewage Treatment Plants

Global ImportancePotent Greenhouse Gas

• Over 30x more potent than carbon dioxide.• Increasing emissions by 1% per year.• Increased by more nitrogen and carbon dioxide.• Primary culprits:

– Wetlands (N)– Termites (N)– Fossil Fuel (MM)– Rice paddies (MM)– Wastes (MM)– Rumen and Enteric (N/MM)– Deforestation Burning (MM)