Phylogenetic analysis by 16S ribosomal DNA sequence comparison reveals two unrelated groups of species within the genus Ruminococcus.

Phylogenetic analysis of the genus Ruminococcus based on 16S rDNA sequence data showed the genus to be phylogenetically heterogenous. Ruminococcus species fall within the radiation of the Bacillus/Clostridium subphylum of the Gram-positive line of descent. Two distinct and unrelated clusters are recovered. One group contains R. flavefaciens, R. albus, R. bromii, and R. callidus. The second group constitutes R. gnavus, R. hansenii, R. lactaris, R. obeum, R. productus and R. torques which together with some Clostridium species may constitute a new genus.