Explanation

Archaebacteria is primitive group of bacteria. The three main groups of archaebacteria are methanogens, halophiles and thermoacidophiles. Methanogens are obligate, anaerobic archaebacteria which oxidize $CO_{2}$ during cellular respiration to produce methane as a waste product. They are found in the musk of swamps and marshes, the rumen of cattle sewage sludges and gut of termites, $e.g.,\ \ Methanococcus\ jannaschii,\ Methanobacterium.$