Abstract
No axenic cultures of Methanothrix soehngenii OpfikonT (T = type strain), exist, nor is any extant contaminated culture known to be derived from strain OpfikonT. I propose strain GP6 as the neotype strain of this taxon. Strain GP6 is the type strain of Methanosaeta concilii and Methanothrix concilii, but both of these names are widely considered to be subjective synonyms of Methanothrix soehngenii.