Methanogens are a type of archaebacteria that occurs in marshes, swamps and rumen of cattles. They are obligate anaerobes that can catabolize acetate and H2 to gaseous products and are used in the final stage 446 called methanogenesis of biogas production in gobar gas plant. Nitrilying bacteria oxidise NH3, into NO2 and later to NO3. Ammonifying bacteria convert proteins into NH3 Denitrifying bacteria reduce NO3, into NH3,.