The primitive prokaryotes responsible for the production of biogas from the dung of ruminant animals, include the:

Archaebacteria are considered as most primitive prokaryote which appeared on earth for the first time as it could survive through the anaerobic harsh environment present that time.

Halophiles, thermoacidophiles and methanogens are archaebacteria.

Methanogens are present in the rumen of cattle that is present in dung as well. It helps in production of methane gas that is a component of biogas.