Phylogenetic analysis of Ruminococcus flavefaciens, the type species of the genus Ruminococcus, does not support the reclassification of Streptococcus hansenii and Peptostreptococcus productus as ruminococci.

The 16S rRNA gene sequence of the type strain of Ruminococcus flavefaciens, the type species of the genus Ruminococcus, was determined by PCR direct sequencing. A comparative sequence analysis showed that R. flavefaciens is phylogenetically related to a small cluster (cluster IV of Collins et al. [M. D. Collins, P. A. Lawson, A. Willems, J. J. Cordoba, J. Fernandez-Garayzabal, P. Garcia, J. Cai, H. Hippe, and J. A. E. Farrow, Int. J. Syst. Bacteriol. 44:812-826, 1994]) of organisms which includes several Clostridium and Eubacterium species. R. flavefaciens was found to be phylogenetically only remotely related to Ruminococcus gnavus, Ruminococcus torques, Peptostreptococcus productus, and Streptococcus hansenii. These findings demonstrate that the genus Ruminococcus is not a monophyletic group, and the proposed transfer of P. productus and S. hansenii to this genus (T. Ezaki, N. Li, Y. Hashimoto, H. Miura, and H. Yamamoto, Int. J. Syst. Bacteriol. 44:130-136, 1994) is not supported.