title: Comparison of 16S rRNA gene sequences of genus Methanobrevibacter.
abstract: BACKGROUND
  The phylogeny of the genus Methanobrevibacter was established almost 25 years ago on the basis of the similarities of the 16S rRNA oligonucleotide catalogs. Since then, many 16S rRNA gene sequences of newly isolated strains or clones representing the genus Methanobrevibacter have been deposited. We tried to reorganize the 16S rRNA gene sequences of this genus and revise the taxonomic affiliation of the isolates and clones representing the genus Methanobrevibacter.
  
  
  RESULTS
  The phylogenetic analysis of the genus based on 786 bp aligned region from fifty-four representative sequences of the 120 available sequences for the genus revealed seven multi-member groups namely, Ruminantium, Smithii, Woesei, Curvatus, Arboriphilicus, Filiformis, and the Termite gut symbionts along with three separate lineages represented by Mbr. wolinii, Mbr. acididurans, and termite gut flagellate symbiont LHD12. The cophenetic correlation coefficient, a test for the ultrametric properties of the 16S rRNA gene sequences used for the tree was found to be 0.913 indicating the high degree of goodness of fit of the tree topology. A significant relationship was found between the 16S rRNA sequence similarity (S) and the extent of DNA hybridization (D) for the genus with the correlation coefficient (r) for logD and logS, and for [ln(-lnD) and ln(-lnS)] being 0.73 and 0.796 respectively. Our analysis revealed that for this genus, when S = 0.984, D would be <70% at least 99% of the times, and with 70% D as the species "cutoff", any 16S rRNA gene sequence showing <98% sequence similarity can be considered as a separate species. In addition, we deduced group specific signature positions that have remained conserved in evolution of the genus.
  
  
  CONCLUSIONS
  A very significant relationship between D and S was found to exist for the genus Methanobrevibacter, implying that it is possible to predict D from S with a known precision for the genus. We propose to include the termite gut flagellate symbiont LHD12, the methanogenic endosymbionts of the ciliate Nyctotherus ovalis, and rat feces isolate RT reported earlier, as separate species of the genus Methanobrevibacter.
authors.affiliation: Molecular Biology Unit, National Centre for Cell Science, Pune-411007, India. abhijitdighe@hotmail.com
authors.forename: Abhijit S
authors.initials: AS
authors.lastname: Dighe
authors.forename: Kamlesh
authors.initials: K
authors.lastname: Jangid
authors.forename: José M
authors.initials: JM
authors.lastname: González
authors.forename: Vyankatesh J
authors.initials: VJ
authors.lastname: Pidiyar
authors.forename: Milind S
authors.initials: MS
authors.lastname: Patole
authors.forename: Dilip R
authors.initials: DR
authors.lastname: Ranade
authors.forename: Yogesh S
authors.initials: YS
authors.lastname: Shouche
mesh_terms: D000818:Animals; D001483:Base Sequence; D016798:Ciliophora / Q000382:microbiology; D019766:Genes, Archaeal; D020459:Genes, rRNA; D041581:Methanobrevibacter / Q000145:classification* / Q000235:genetics; D008969:Molecular Sequence Data; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000145:classification* / Q000235:genetics; D016415:Sequence Alignment
chemical_list: D012336:RNA, Ribosomal, 16S