The genus
Methanothermococcus are cocci that use the substrates H
2 + CO
2 and formate for methanogenesis. Their DNA %GC is 31-34.
Taken from the text Brock Biology of Microorganisms (10th ed.). Madigan, M.T., Martinko, J.M., and Parker, J. 2003. Prentice Hall. 454p.