Abstract
The validation of gas-vacuolated strains of methanosarcinae at the species level under the name of Methanosarcina vacuolata sp. nov. is presented, based on chemotaxonomic as well as morphological characteristics. M. vacuolata is shown to be related but distinct from the type species M. barkeri and the other species of freshwater methanosarcinae, M. mazei and M. thermophila.