Question

What are Methanogens? Name the animals they are present in and the role they play there.

Answer 1

Methanogens are prokaryotes and belong to the domain of archaea. They play an important role in anaerobic wastewater treatments. There are over fifty species of methanogens. They are mostly anaerobic organisms and cannot function in an aerobic environment. Since they live in extreme anaerobic conditions, they are also called extremophiles. They are found in diverse habitats associated with decomposition of organic matter, aquatic sediments, geothermal springs etc.

Complete answer:
Methanogens are microorganisms that produce methane as a metabolic by product in low oxygen conditions. The process of producing methane is known as methanogenesis. It was first demonstrated by Alessandro Volta. During methanogenesis a unique variety of enzymes are involved. They produce methane in strictly anaerobic conditions.
Methanogens are present in the rumen and intestinal system of animals, anaerobic protozoans, marine sediments, human oral cavity, guts of insects etc. It helps to digest plant biomass and produces methane released into the environment in the intestine of herbivorous animals. Methanogens produce methane from substrates such as $\dfrac{{{H_2}}}{{C{O_2}}}$, acetate, methanol and methylamines.
Based on shape, $16s$ rRna sequence, cell wall structure, membrane lipid features, Methanogens can be divided into five orders. They are Methanobacteriales, Methanococcales, Methanomicrobiales, Methanosarcinales and Methanopyrales.

Note:
Methanogens play a vital role in the ecosystem by removing excess hydrogen and fermentation products produced by other forms of anaerobic respiration. They are widely used in anaerobic digesters to treat wastewater and aqueous organic pollutants. Methane produced by them is an energy source for heat and electricity. They are also responsible for flatulence in humans.