Strictly anaerobic archaebacteria, able to use only a very limited substrate spectrum (e.g. molecular hydrogen, formate, methanol, methylamine, carbon monoxide or acetate) as electron donors for the reduction of carbon dioxide to methane.
Source:
PAC, 1992, 64, 143. 'Glossary for chemists of terms used in biotechnology (IUPAC Recommendations 1992)' on page 160 (https://doi.org/10.1351/pac199264010143)