Methanogenesis is the biological production of methane through two pathways. It is carried out by methanogenic archaea under strictly anaerobic conditions. These archaea use one-carbon compounds like carbon dioxide, methanol, or methylamines as substrates. They reduce these substrates using coenzymes like coenzyme M, coenzyme F420, methanofuran, and tetrahydromethanopterin to produce methane as the end product through a series of reduction steps. Methanogenesis provides an important source of energy for the methanogenic archaea in environments like wetlands, digestive systems, and anaerobic digesters.

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2. • Methanogenesis is the biological production of CH4 from either
CO2 plus H2 or from methylated organic compounds.
• Process of methanogensis was first demonstrated over 200
years ago by Alessandro Volta.
• The process is strictly anaerobic.
• All known methanogenic bacteria belong to Archaebacteria.
• They are also called methanogens.
• A variety of unique coenzymes are involved in methanogenesis.

3. Methanogens belong to the Archaea group of Prokaryotes.
They can be classified as Chemolithotrophic methanogens and
Methylotrophic methanogens.
Methanogenic bacteria are extremely oxygen sensitive.
Methanogens require anaerobic conditions .
They are found in the digestive systems of herbivores, marshes or
lake bottoms, all sorts of mud sediments and in man made
anaerobic digestors in sewage treatment plants.

4. Complex organic compounds cannot be utilised by methanogens.
They use only C1 compounds and the only C2 compound: Acetate.
There are two nutritional groups of methanogens.
• Obligate chemolithotrophic methanogens that grow with CO2 plus H2
according to the equation:-
CO2 + 4H2 CH4 + 2H2O
• Some of these organisms live with the Quasi-chemolithotrophic
substrates HCOOH and CO
4HCOOH 4CO2 + 4H2
CO2 + 4H2 CH4 + 2H2O

5.  Methylotrophic methanogens that grow with methyl group containing
substrates for eg. Methanol, methylamines, acetate
 The reaction for acetate is:
CH3COOH CH4 + CH2
 Organisms such as Methanosarcina barkeri grow on methanol or
methylamines. Here, one fourth of the substrate has to be oxidised to CO2
for reducing power generation.
CH3OH + H2O CO2 + 6H
3CH3OH + 6H 3CH4 + 3 H2O
4CH3OH 3CH4 + CO2 + 2 H2O
 Group 2 organisms produce methane directly from methyl groups and not
via CO2.
 Obligate chemolithotrophic methanogens do not contain cytochromes
which are present in methylotrophic methanogens

7. • The first two novel coenzymes discovered in methanogens are
coenzyme M and coenzyme F420
• Coenzyme M is a simple chemical compound . Its reactive group is the
mercepto group which can be methylated and methyl coenzyme M is
the ultimate precursor of mehane.
• Coenzyme F420 is a deazaflavin, it is a redox carrier and its role is
analogous to that of ferrodoxin in other anaerobes.
• It functions as electron acceptor of hydrogenase and as electron donor
in several reduction reactions.
• Tetrahydromethanopterin and Methanofuran are involved in CO2
reduction. Methanofuran is the primary CO2 aceeptor.

8. Methane formation from CO2 and H2 by Barker’s scheme.
• The first carrier molecule is Methanofuran.
• In a reaction that requires CO2 and reducing equivalents it is
converted to formylmethanofuran with the formyl group
residing at the aminomethyl group of the furan ring.
• Transfer of the C1 moiety to tetrahydromethanopterin and
reduction of the formyl to methyl group follows.
• It is finally transferred to the Coenzyme M and is reduced to
CH3 by the enzyme methyl co enzyme M methylreductase.

10. Formation of methane from bicarbonate
• The four steps leading to formation of methane from
bicarbonate are as follows
HCO3- + H2 → HCOO- + H2O
HCOO- + H2 + H+ → CH2O + H2O
CH2O + H2 → CH3OH
CH3OH + H2 → CH4 + H2O
HCO3 + H+ + 4H2 → CH4 + 3H2O
• The fourth step is coupled to the generation of proton motive
force at the membrane which in turn is used by an ATP synthase
for the phosphorylation of ADP to produce ATP.
• Eg. Methanosarcina barkeri

11. Formation of methane from Acetate
• Methanosarcina barkeri is a classic and representative species for
those methanogenic bacteria that utilize acetate, methanol and
methylamine as substrates.
• Formation of methane from acetate is a oxidoreduction process.
• First CO and methyl coenzyme M are produced which is the
precursor for methane. CO2 is also produced.

12. Formation of methane from Methanol and Methylamine
Methanogenesis of methanol and methylamine can be subdivided
into two processes:
• Oxidation of one fourth of the methyl groups to CO2
• Reduction of three fourth methyl groups to CH4.
• A methanol:coenzyme M and a trimethylamine:coenzyme M
methyltransferase have been characterized.
• The methyl group is first transferred to the protein bound 5
hydroxy benzimidazolylcobamide.
• Methyl groups transfer further proceeds to coenzyme M.